AN ABSTRACT OF THE THESIS OF
William D. Head for the degree of Doctor of Philosophy in Fisherj!!
and Wildlife presented on April 25, 1984.
Title: An Assessment of a Closed Greenhouse Aquaculture and
for privacy
::::::::: Redacted
/7
James E. Lannan
Research was conducted to address three objectives:
1.
To
determine the nitrogen cycling of a closed
greenhouse aquaculture and hydroponic system;
2.
To determine the energy budget of a closed greenhouse
aquaculture and hydroponic system; and
3.
To determine which low cost fish diets could be used
as a replacement or supplement to commercial diets for Ti1ap
mossambica.
A
6,435
liter recirculating aquaculture system
was
2
enclosed in a 32.6 m greenhouse.
Water was recirculated through
two 416 liter trickling filter towers and three 5.5 m long hydroponic
troughs.
The aquaculture tank was stocked with a polyculture of
channel catfish (Ictalurus punctatus) and tilapia (Tilapia
mossambica) and the hydroponic troughs were planted with tomatoes
(Lycopersicon eseulentum).
The fishes were fed a commercial fish
diet and the tomatoes were irrigated with the aquaculture water
using a modified Nutrient Film Technique.
The fish yield was 42.2 kg and the average tomato yield
from 24 plants was 4.1 kg/plant. The combined fish and tomato
production accounted for 65% of the total nitrogen input. Leaf
analyses and visual inspection showed that the tomato plants from
the hydroponic troughs were deficient in potassium and magnesium.
An energy analysis of the greenhouse and aquaculturehydroponic system showed that when combining the energy outputs
of heat, fish, and tomatoes the energy ratio (energy output/energy
input) was similar to literature values for milkfish pond culture.
When only the fish production was considered the energy ratio was
similar to literature values reported for intensive water
recirculating systems.
Azolla
(A.
mexicana),
water
hyacinth
(Eichhornia
crassipes) and earthworms (Eisenia foetida) were evaluated as diets
for Tilapia mossambica. T. mossambica fed a pelleted water
hyacinth diet had the lowest specific growth rates. T. mossambica
fed a pelleted diet of Azolla supplemented with 10% earthworm meal
or the same diet supplemented with 50% commercial catfish ration
had specific growth rates that were not significantly different than
T. mossambjca fed an all commercial ration.
An Assessment of a Closed Greenhouse
Aquaculture and Hydroponic System
by
William D. Head
A THESIS
submitted to
Oregon State University
in partial fulfillment of
the requirements for the
degree of
Doctor of Philosophy
Completed April 25, 1984
Commencement June 1984
Redacted for privacy
J.E. ,annãñ,
ate Professor of Fisheries in charge or njor
Redacted for privacy
of Lpar
of'Fishéries and Wild
Redacted for privacy
of Gr
Late thesis is presented
April 25, 1984
Typed byW.D. Head for
WilliamD. Head
e
ACKNOWLEDGEMENTS
My sincere thanks go to my committee members, Dr. Jim
Lannan, Dr. Carl Bond, Dr. Larry Small, Dr. Court Smith, and Dr. Ed
Anderson, for their support and encouragement to develop
independent and critical thinking.
The Amity Foundation of Eugene, Oregon provided the
research site and organizational framework for acquiring funds for
this project and many people of the Eugene community assisted with
different aspects of the research. I regret that there is not
enough room to list and thank all of them.
This research was funded through grants from the Oregon
State Community Services Program, the Oregon Department of
Energy, the United States Department of Energy, the National
Council on Aging, the National Center for Appropriate Technology,
and Titles I and VI of the Comprehensive Employment and Training
Act.
This thesis is dedicated to Katherine Stewart for her
unselfish sacrifices and enduring love and to my parents, Edythe and
Mel, for their unwavering optimism.
TABLE OF CONTENTS
PAGE
GENERAL INTRODUCTION AND LITERATURE REVIEW
1
I. AN ASSESSMENT OF THE INTEGRATION OF
HYDROPONIC FOOD PRODUCTION WITH
A CLOSED AQUACULTURE SYSTEM
10
Introduction
Materials and Methods
Results
10
14
Discussion
48
31
II. AN ENERGY ANALYSIS OF A CLOSED GREENHOUSE
AQUACULTURE AND HYDROPONIC SYSTEM
Introduction
Materials and Methods
Results
Discussion
III. GROWTH RESPONSES OF TILAPIA MOSSAMBICA
FED COMBINATIONS OF AZOLLA, WATER
HYACINTH AND EARTHWORM MEAL
Introduction
Materials and Methods
Results
Discussion
54
54
57
61
79
84
84
88
96
100
CONCLUSIONS
107
BIBLIOGRAPHY
113
LIST OF FIGURES
FIGURE
1.1
Solar greenhouse details.
1.2
Solar greenhouse cross section.
Solar greenhouse framing and glazing detail.
Solar greenhouse aquaculture and
hydroponic cross section.
Plan view of solar greenhouse and
1.3
1.4
1.5
hydroponic system.
1.6
I.?
111.1
Nitrate, nitrite, ammonia and pH values.
Water temperature, turbidity, phosphate,
and oxygen values.
Tanks (190 liter), filter, and aeration
system used for feeding trials.
PAGE
16
18
20
23
25
35
37
93
LIST OF TABLES
PAGE
1.1
Solar greenhouse specifications.
1.2
Nitrogen testing and analytical methods.
Water quality testing.
1.3
1.4
1.5
1.6
1982 fish stocking, harvest weights and
specific growth rates.
Percent male and female Tilapia mossambica.
Loading and carrying capacity factors for
combined T. mossambica and I. punctatus
weights.
1.7
1.8
1.9
1.10
11.1
Tomato yield from the greenhouse hydroponic
and soil systems.
Nutritional content of soil-grown and hydroponicgrown tomato leaves, and fish pellets, plus
literature values for deficient, sufficient
and excessive amounts of tissue elements.
Nitrogen content as percent of dry weight.
Nitrogen balance in a closed recirculating
system for the culture of tilapia, channel
catfish, and hydroponic tomatoes.
Useful life of greenhouse, aquaculture, and
hydroponic systems.
11.2
Embodied energy values of grenhouse materials.
11.3
Embodied energy values of trickling filter
materials.
11.4
11.5
11.6
11.7
Embodied energy values of hydroponic materials.
Construction labor energy.
15
27
29
32
33
34
43
44
45
46
60
62
63
64
65
Percent energy contribution of construction
materials and labor.
66
Amortized energy costs of materials and
labor, and annual operating energy costs.
67
LIST OF TABLES (continued)
PAGE
11.8
11.9
11.10
11.11
Percent annual energy contribution of
amortized and operating costs.
Average monthly and annual heat contribution
from the greenhouse aquaculture tank.
1982 fish stocking and harvest.
Annual energy output and percent contribution
of a closed greenhouse aquaculture and
hydroponic system.
11.12
11.13
11.14
11.15
111.1
111.2
111.3
111.4
111.5
111.6
Energy effidency ratios (E0/E1).
Energy payback in years.
Energy required to produce a unit weight of
fish or tomato.
68
70
71
73
75
76
78
Energy requirements for different aquaculture
systems.
Percent composition of test diets.
Proximate analysis of tilapia test diets.
Nutritional requirements of tilapia.
Specific growth rates and water quality of
five feeding trials.
Mean percent weight loss of pellets immersed
in water 20 minutes.
Amino acid profiles of methionine, lysine,
and arginine.
80
89
90
92
97
99
101
AN ASSESSMENT OF A CLOSED GREENHOUSE
AQUACULTURE AND HYDROPONiC SYSTEM
GENERAL INTRODUCTION AND LITERATURE REVIEW
Fish culture in the United States has been limited mainly
to commercial facilities using large quantities of energy, water,
and high protein feed. In intensive systems typical of North
American trout and catfish aquaculture energy subsidies of 10 to 60
times the energy contained in the fish are required (Edwardson,
1976; Pitcher, 1977; Rawitscher and Mayer, 1977; Pimentel and
Pimentel, 1979). Thus North American aquaculture can be more
energy intensive than competing agricultural systems such as feed
lot beef, hog rearing, and broiler chickens (Pimentel et al., 1975).
The energy picture is even bleaker as the rest of the food
system (processing, transporting, storing, marketing, and domestic
preparation) uses about four times more energy than that used in
fish production (Steinhart and Steinhart, 1974). It is doubtful that
these systems will be sustainable in the near future when energy
will be even more costly and in short supply. Rising energy costs
have pushed the price of fish up proportionally and opened the door
for new approaches to fish culture.
One type of aquaculture that is now receiving attention is
an ecological approach that both conserves energy and makes
maximum use of renewable energies, recycles nutrients, employs a
diversity of speices, and integrates with other food production
systems.
2
This ecological approach to aquaculture has its origins in
the 2,000 year old Chinese polyculture pond system. As many as six
species of carp and other fish species are reared in farm ponds.
The ponds receive animal and vegetable wastes, manure from pigs,
chickens, ducks and humans, and water from the farm ponds is used
to irrigate and fertilize land crops. Periodically the bottom sludge
is removed and utilized as fertilizer for vegetable crops (J3ardach
et al., 1972; Tapiador et al. 1977; UNDP, 1979). Such integration
increases the profit from fish culture by 30 to 40 percent, increases
the overall farm income, allows the farm community to become self
sufficient in food production and greatly reduces, or eliminates, the
need for purchased fertilizers (Tapiador et al., 1977; UNDP, 1979).
In the United States and Canada ecological approaches to
aquaculture are being conducted from the small family-sized scale
to the commercial level. Small, closed system aquaculture is being
proposed as a potentially valuable part of the family-sized food
production system. The goal of this approach is to develop
facilities that are inexpensive, productive, and ecologically stable.
Work is being carried out in this area by a number of groups:
Foundation for Self-Sufficiency (Welsh, 1977); Amity Foundation
(Head and Splane, 1979); New Alchemy Institute (Zweig et al., 1979;
Engstrom et al., 1981); Goddard College (Pierce, 1980); Auburn
University (Rakoy and Allison, 1980); The Ark Project (MacKay and
Van Toever, 1981); Rodale Research Center (Van Gorder and
Strange, 1983).
On a commercial level aquaculture is being integrated with
greenhouse agriculture and rabbit rearing (Ferguson, 1982) and is
3
receiving considerable attention for sewage treatment (Ryther,
1975; Ryther et al., 1975; Huguenin, 1975; Mann and Ryther, 1977;
Duffer and Moyer, 1978; Serfling and Alsten, 1979; Serfling and
Mendola, 1979; Stewart et al., 1979).
of
The model that this research addresses is the integration
aquaculture to solar greenhouse systems. Conventional
greenhouse horticulture is energy intensive and requires substantial
inputs
of heat and electricity (Heichel,
1976;
Leach, 1976).
Through the integration of aquaculture to a solar efficient
greenhouse considerable savings of energy, nutrient, and material
resources are possible. For example, the water acts as thermal
storage for the greenhouse and the greenhouse enables the water to
reach temperatures that promote rapid fish growth. The nutrient
rich water from the fish culture tank can be used to irrigate and
fertilize vegetable crops, and the vegetable crops can, in turn,
remove metabolites toxic to fish.
Solar greenhouse design has just recently been documented
(Clegg and Watkins, 1978; Magee, 1978; McCullagh, 1978; Mazria,
1979; Aiward and Shapiro, 1980; Yanda and Fisher, 1980). Three
design features distinguish a solar greenhouse from a conventional
all glass or plastic greenhouse:
1.
The glazed surface faces south and
is
angled to
capture the low winter sun;
2. Areas not receiving direct winter sun, such as the
north wall and roof, are solid and well insulated to minimize heat
loss; and
3.
Excess solar energy is stored in massive objects like
4
containers of rock, earth, or water. This stored heat is later
released to the greenhouse at night and during cloudy periods.
The purpose of these features is to increase the input of
solar energy and to store it as heat. A conventional greenhouse
does not have a way of naturally storing solar energy and requires
electricity, gas, or oil for supplemental heating to prevent wide and
sudden temperature fluctuations. Ideally a solar greenhouse needs
nothing other than the sun for heat and light.
Although water will store more heat in less space than any
other common heat storage material (Mazria, 1979), the volume
needed to moderate temperatures still requires a lot of space in a
greenhouse.
Using this water for aquaculture and hydroponics can
greatly increase the productivity of solar greenhouses.
Coupling aquaculture with the water heat storage of
greenhouses has had limited attention. The New Alchemy Institute
has done pioneering work in this field (Zweig, 1980).
Most of their
work has been with 2,300 liter translucent fiberglass ponds.
These
"solar algal ponds" act as passive solar collectors and promote algal
growth, which purifies fish wastes. Although high total yields
have been achieved, individual fish size is usually small. Other
groups that have tried greenhouse aquaculture include: The Walden
Foundation (Dekorne, 1975); The Foundation for Self-Sufficiency
(Welsh, 1977); Sun Experimental Farms (Mackie and Mackie, 1977);
Ecotope Group (Brown et al., 1979); and The Ark Project (Van
Toever, 1979).
All of these groups have had limited success. The major
problems have been in system design, producing edible size fish, and
5
low yields.
These problems are related to species selection,
temperature, water quality, and feed.
Species Selection
A variety of fish have been tried in greenhouse systems.
These include:
Tilapia
(Tilapia aurea,
T.
mossambica,
T.
zulu):
Mclarney and Todd, 1974; Mackie and Mackie,
1977; Welsh, 1977; Zweig, 1977: Brown et al.,
1979; Zweig, 1979.
Carp (Cyprinus carpio):
Zweig, 1979; Brown et al., 1979.
Bullhead Catfish (Ictalurus nebulosus):
Zweig, 1979.
Bluegill (Lepomis macroehirus): Dekorne, 1975.
Largemouth Bass (Micropterus salmoides): Mackie and
Mackie, 1977.
Trout
gairdneri, Salvelinus fontinalis): Van
Toever, 1979; MacKay and Van Toever, 1981.
Atlantic Salmon (Salmo salar): Van Toever and Mackay,
(Salmo
1980.
To date the cited authors have had limited success with
greenhouse aquaculture. Low yields and small size are the most
common problems.
In addition most authors do not discuss the
quality of the cultured fish.
Fish reared in small enclosed systems
may develop off-flavors imparted by the quality of the water and
unfavorable algae blooms (Hepher and Pruginin, 1981).
Water Temperature
Water temperature plays a major role in regulating fish
metabolism and growth. Warm water fish such as catfish, tilapia,
common carp, large-mouth bass, and bluegill grow best at a
temperature range of 27-32°C whereas rainbow trout grow best
between 15-17°C (Colt et al., 1979). Water temperatures in solar
greenhouse aquaculture systems I investigated did not maintain
optimum growing temperatures long enough for good fish growth.
Often the water storage system was not in direct light and remained
cool even in the summer (Dekorne, 1975; Mackie and Mackie, 1977;
Zweig, 1977) or the greenhouse was not insulated properly (Welsh,
1977; Brown et al., 1979) and lost heat quickly. Coupling the needs
of greenhouse heat storage and aquaculture is still a challenge.
Water Quality
In order for the water in a solar greenhouse to act as heat
storage it cannot be changed frequently with cold fresh water.
Although some greenhouse systems have been used in attempts to
raise fish without filtration (Mackie and Mackie, 1977; Zweig, 1979)
most designs incorporate recirculation and biological filtration
(Mcbarney and Todd, 1974; Dekorne, 1975; Welsh, 1977; Brown et al.,
1979; Van Toever and Mackay, 1980).
However, all of these filter
designs failed to maintain high enough stocking densities for
productive yields.
One problem with biological filtration in recirculating
systems is the accumulation of nitrate and phosphate as end
products (Meade, 1974). To reduce this buildup recirculating
systems are generally designed to discharge 10% of the total water
volume per day (Liao and Mayo, 1974).
If aquaculture systems are
to serve as thermal heat storage for solar greenhouses replacing
10% of the volume per day with incoming cold fresh water
7
represents an undesirable heat loss to both the aquaculture system
and greenhouse environment. Connecting recirculating aquaculture designs to hydroponic plant production provides a way Of
using biofiltration by-products and conserving heat. Plants in a
hydroponic unit can use these elements in growth and produce
vegetables as a marketable by-product. Only a few researchers
have attempted to integrate greenhouse aquaculture with
hydroponic horticulture (Dekorne, 1975; Landesman, 1977; Mackay
and Van Toever, 1980; Pierce, 1980; Baum, 1982). These studies
have had mixed success. Most did not have thorough enough testing
so that evaluations or recommendations could be made.
Fish Feed
The cost of feeding fish can account for over 50% of the
operating expense in aquaculture practices (Hastings, 1969;
Goldman and Ryther, 1975; Burke and Waidrop, 1978). The high
cost of fish food is due to its high protein content, processing,
packaging, and transportation.
The energy embodied in the feed
(i.e. the energy required to catch the fish, grow the crops, prepare
and transport the feeds) can compose up to 73% of the major energy
subsidy in intensive trout culture (Edwardson, 1976).
One way to
reduce this high energy cost is to raise fish that feed low on the
food chain and to feed them locally grown food sources.
Various
supplemental
feeds
have
been
tested
as
alternatives to commercial diets. Some work has been done raising
tilapia on earthworms (McLarney and Parkin, 1977), midge larvae
and flying insects (McLarney and Parkin, 1982) and a variety of
plant protein diets (Wu and Jan, 1977; Davis and Stickney, 1978;
Fl]
['1
Jackson et al., 1982). However, there have been no reported
studies on the use of dried and pelleted water fern (Azolla) or
water hyacinth (Eichhornia crassipes) as sources of plant protein
for tilapia diets. These aquatic plants have a high protein content
and extremely fast growth rates (Moore, 1969; Wolverton and
McDonald, 1976).
Both the water fern and the water hyacinth
could make suitable low cost fish food substitutes.
Growth of fish using livestock manures as a food source
has been investigated recently (Buck, 1977; Schroeder, 1978;
Wohlfarth, 1978; Burns and Stickney, 1980; McGeachin and Stickney,
1982; The New Alchemy Institute, 1982). Although using manures
as a food source has proven to be somewhat successful in open ponds
it would not be a recommended method of feeding fish in a
recirculating system because of dissolved nutrients which would
overload filter systems by promoting bacterial growth.
Energy
In assessing greenhouse aquaculture it is important to
determine how much energy is required for the construction and
operation of the facility relative to the energy, food and other
benefits the greenhouse facility provides. There are no studies
which have investigated the energetics of closed greenhouse
aquaculture and hydroponic systems.
Edwardson (1976) compared
the energy requirements for different types of aquaculture systems,
and his analysis showed that conventional recirculating designs are
the most energy intensive of the ones he studied. He did not,
however, consider a closed system that maximized energy use by
biological integration.
evaluated the energetics of 2,300 liter
fiberglass aquaculture tanks, but his he did not take into account
Wolfe (1980)
the energetic costs of the greenhouse it was enclosed in. Because
of this his estimate of the energetic costs of the aquaculture design
he studied is unreasonably low.
A detailed energy accounting of a greenhouse aquaculture
and hydroponic system will reveal major energy costs and serve as a
guide for design and operating modifications.
Goals and Objectives
The goals of this thesis are to evaluate the integration of
closed greenhouse aquaculture and hydroponic horticulture and to
test low cost fish diet substitutes.
This thesis is presented in manuscript form and addresses
three specific objectives:
1.
To determine the fish and plant production, and
nitrogen cycling of a closed greenhouse aquaculture and hydroponic
system;
2.
To determine the energy budget of a closed greenhouse
aquaculture and hydroponic system; and
3.
To determine which low cost fish diets could be used
as a replacement or supplement to commercial diets for Tilapia
mossambica.
'Is]
CHAPTER 1
AN ASSESSMENT OF THE INTEGRATION OF HYDROPONIC
FOOD PRODUCTION WITH A CLOSED
GREENHOUSE AQUACULTURE SYSTEM
INTRODUCTION
There are various biological methods available to treat
water for reuse in intensified fish culture (Speece, 1973; Liao and
Mayo, 1974; Meade, 1974; Parker and Simco, 1974; Kinne, 1976; Lewis
and Buynak, 1976; Wheaton, 1977; Zweig, 1977; Spotte, 1979; Van
Gorder, 1980; Parker, 1981). A major problem with biological
filtration in recirculating systems is the accumulation of nitrate
and phosphate as end products (Meade, 1974; Naegel, 1977). To
reduce this buildup recirculating systems are generally designed to
discharge 10% of the total water volume per day (Liao and Mayo,
1974).
This represents a substantial nutrient and thermal storage
heat loss.
If aquaculture systems are to serve as thermal heat
storage for greenhouses replacing 10% of the volume per day with
incoming cold fresh water represents an undesirable heat loss to
both the aquaculture system and greenhouse environment.
Connecting
recirculating greenhouse aquaculture designs to
hydroponic plant production provides a means of using biofiltration
by-products and conserving heat.
A number of researchers have attempted to integrate
11
aquaculture with hydroponic horticulture.
Most of the designs
were outdoor systems that were flow-through (Sneed et al., 1975),
pond (Loyacano and Grosvenor, 1973; Rundquist et al., 1976) or
recirculating (Lewis et al., 1978; Rakocy and Allison, 1979; Sutton
and Lewis, 1982).
Only a few researchers have attempted to integrate
greenhouse aquaculture with hydroponic horticulture. Dekorne
(1975) used water from a greenhouse aquaculture tank to irrigate
gravel hydroponic beds.
His system was very tedious, however, as
it required lifting a 19 liter bucket full of water from the fish tank
at least three times a day to gravity feed the hydroponic beds. He
also did not try to integrate the hydroponic system and the
aquaculture system by recycling the water back into the fish tank.
Although Dekorne initially got good growth using the water from
the fish culture system, plants did not do as well as those watered
with a commercial hydroponic solution.
Landesman
connected a hydroponic vegetable
system to a recirculation tank used to overwinter tilapia. Nitrate
(1977)
and phosphate accumulated in his system because the water from the
tilapia culture passed through the hydroponic tank before entering
the biofilter. He had success growing collard greens and Bibb
lettuce but got poor tomato yields.
MacKay and Van Toever (1980) used circular translucent
1,700 liter tanks (1.2 m wide and 1.5 m high) in a combined salmonid
and gravel hydroponic culture. Their system, however, was set Up
in a poorly lit area of their greenhouse and the short length of the
experimental period (43 days) did not allow the plants to mature so
12
no yield data were obtained.
Pierce (1980) used a 4,920 liter septic tank for thermal
storage and aquaculture in a solar greenhouse having both active
and passive collectors. Water from the fish tank was recirculated
through two 1.44 m 2 gravel beds planted with tomatoes and
watercress. Without explanation Pierce harvested the tomatoes
before they were ripe and got a wet weight yield of watercress of
3
11.2 kg/rn of biofilter volume.
Researchers
at
Institute have
incorporated hydroponics to recirculating greenhouse aquaculture
the
New
Alche'my
(Baum, 1982).
Their design was composed of three translucent
2,300 liter tanks, an upwelling biofilter, a 155 liter settling basin
and a 4.9 m long hydroponic trough. Water passed through the
biofilter and settling tank before circulating through the
hydroponic trough.
They reported a harvest of 28 kg of tomatoes,
1.3 kg of lettuce, 1.6 kg of sweet basil and 0.5 kg of cucumbers from
the hydroponic trough. The plants showed signs of being deficient
in iron, magnesium and potassium, and Baum reported trouble with
aneorobic zones and hydrogen sulfide production in the hydroponic
trough. The hydroponic system had only an incidental effect on
nitrogen removal as only 6% of the nitrogen input was removed by
plants.
Fish production was about half of the production from
aquaculture systems without hydroponics.
The New Alchemy design was very labor intensive as it
required weekly flushings of the hydroponic trough, one to three
sediment discharges daily, plant fertilizer applications, twice daily
fish feeding, and maintenance and regulation of air-lift pumps, an
13
air compressor, and an aquarium air pump.
If the integration of hydroponics
to
greenhouse
aquaculture is to be successful, less labor intensive and more
productive designs need to be developed and tested. The purposes
of this experiment were to evaluate a greenhouse aquaculture and
hydroponic design for fish and plant production and to determine
the nitrogen partitioning among the biological components.
14
MATERIALS AND METHODS
Solar Greenhouse
2
The 32.6 m solar greenhouse was of A-frame design with
its long axis facing east-west and only the south-facing side
glazed. Other portions of the greenhouse were opaque and
insulated to reduce heat loss. The back wall was sloped and
covered with aluminum foil to direct light into the heat storage and
aquaculture tank. Table 1.1 gives greenhouse specifications and
Figures 1.1 - 1.3 present greenhouse details.
Aquaculture System
The aquaculture system consisted of a concrete tank (5.5m
x l.54m x 0.9m deep) connected to a recirculating trickling filter
system. The fish tank held 6,435 liters of water and served as heat
storage for the solar greenhouse. The trickling filter consisted of
50 wooden pallets (40.6 cm x 40.6 cm x 3.8 cm) stacked in two 416
liter towers. Oyster shells in a plastic net above the pallets
provided a calcium carbonate buffer, and a 62.5 liter void area
below the filter outflow served as a sediment trap. A 3.8 cm gate
valve was threaded to the bottom of each sedimnent trap for easy
drainage. A 1/15th horsepower submersible pump (Little Gianttm)
was used to circulate the water. Flow rates were measured at
24.25 liters/minute. Figure 1.4 presents details of the trickling
filter.
Hydroponic System
Three flat bottomed PVC troughs were connected to the
filter outflows and ran the 5.5 m length of the fish tank. The
troughs were suspended by guy wires secured to the greenhouse
15
Table 1.1.
Solar greenhouse specifications.
Feature
Specification
Location
Eugene, Oregon
Orientation
21 degrees west of true south
Glazing angle
60 degrees
Glazing area
22.3 m2
Backwall angle
52 degrees
Floor area
32.6 m2
16
Figure 1.1. Solar greenhouse details.
17
SOUTH WALL'
WALL
Wood latch
Insulating panel up
Weather-seating tr.nis
Galvanlz.d flashing
Roll roofing
FILTER SYSTE
1Aaphalt felt
I!
Gtazrng south wall:
Outside - Kah
tibergi
Inside-
'tsi Pi/4.._______
Insulating
Earth
1]
Cedar slit plates
douglas fir studs for north
& end walls
\W\
plywood cov.rs
solid waS framing
Foundation standard floating
slab-on-grade construction
Figure 1.1
ifi
II
Figure 1.2.
Solar greenhouse cross section.
19
Galvanized flashing
Roofing and felt
Weather strip
Glazed south
wall
\\
p-plywood
Fiberglass insulation
Tempered masonite
Reflecting foil
2.9m
Cedar sill
plates
£
Nort
Back fill
im
I
3.5m
Figure 1.2
20
Figure 1.3. Solar greenhouse framing and glazing detail.
21
GALVAMZED FLASHING
CDX PLYWOOD
INSULATION
KALWALLfJJ.-''
ROLL ROOFING
5.1 x 15.2 cm
FELT
lxlO.
ALUMINUM NAIL
NEOPRENE
WASHER
BAT TEN
FIBERGLASS-7Jf
RIBBON CAULKi'l.) )
I
WOOD FRAMING
POLYETHELE N
BATTENSTAPLES
Figure 1.3
22
rafters. The top of the troughs were covered with 4-mu black
polyethylene to keep roots moist and prevent the growth of algae.
Plastic valves at the filter outflow controlled the amount of water
flowing through the hydroponic troughs. The flow was adjusted so
water left the trough in a thin but continuous stream. Flow rates
were measured at 2 liters/minute/trough.
Excess water from the
filters was shunted directly into the fish tank through a by-pass
outlet (Figures 1.4 and 1.5).
Tomato seeds (Lycopersicon esculenturn, Vendor variety)
were started in peat pots filled with vermiculite. After six weeks
the seedlings and peat pots were tanspianted through slits made in
the plastic. The peat pots provided support for the young plants
and allowed the roots to grow into a common root mass.
Fish Stocking
The aquaculture tank was stocked with 120 tilapia (Tilap
and 60 channel catfish (Ictalurus punctatus). The
fish were fed twice daily at three percent of their body weight daily
with a commercial fish pellet (Purina trout chow"). The fish were
periodically crowded to one end of the tank and were sampled for
weight gain. Feeding rates were recalculated from weight gain
mossambica)
measurements.
Nitrogen Pathway
To determine the nitrogen pathway the analytical methods
outlined in Table 1.2 were used.
Total nitrogen in the feed was determined using a PerkinElmer
Model
240B
Elemental
Analyzer. The
Perkin-Elmer
Elemental Analyzer is based on an improved Dumas nitrogen method
Figure 1.4.
Solar greenhouse aquaculture and hydroponic cross section.
N)
Is
oysteC
-A
Filfer- fôwe.r
fi
Fi9ure 1.4
V
KENHOU6E AVACVLTVR/ t-IyI?ROPCNI(
6YSTfr\
.
L-75c.v),--1
Hydropoiiic
'I
I
I
J4
(
N,
-
Figure 1.5.
Plan view of solar greenhouse and hydroponic system.
N)
C,,
LA
VIEW OF
6OLAF-
G,gE.NHOU5E
Figure 1.5
27
Table 1.2.
Nitrogen testing and analytical methods.
Source
Method of Analysis_
Nitrogen in feed
Elental Analyzer
Nitrogen in fish
El-rntal Analyzer
Nitrogen in tcmato plant & fruit
Elanental Analyzer
Nitrogen in sludge (particulate)
Elental Analyzer
Dissolved nitrogen in sludge
Nesslerization
Diazotizat ion
cadmium reduction
Nitrogen in tank (particulate)
E1Qnental Analyzer
Dissolved Nitrogen in tank
NH3.N
2-N
Nesslerization
Diazotization
cadmium reduction
that employs a large excess of oxygen for combustion. This method
is more sensitive than the macro-Kjeldahl nitrogen method (Culmo,
Nitrogen uptake by fish was determined by obtaining net
harvest weights and taking samples for dry weight and nitrogen
content. Particulate nitrogen in the sludge was determined by
1979).
draining the sludge into calibrated 190 liter containers for volume
measurements and sampling. The sludge was mixed well and a
known volume was filtered through a GF/C glass fiber filter to
collect particulates. These samples were analyzed on the
elemental analyzer. The filtrate was analyzed for dissolved
inorganic nitrogen (NH -N, NO -N, NO -N) with a Hach DR/2
3
spectrophotometer. This
2
instrument
3
is
approved
by
the
Environmental Protection Agency for water testing and reporting.
Standardization tests were made to check reagent strength and
technique.
In
addition
the
spectrophotometer was checked
periodically to verify linearity and wavelength accuracy. During
the testing period triplicate samples were taken for analysis.
Nitrogen (particulate and dissolved) in the fish tank was measured
using the same methods described for the sludge treatment.
Nitrogen in the hydroponic tomatoes was determined by taking
samples of roots, stems, leaf, and fruit, drying at 60°C and
quantified using the elemental analyzer.
During the experimental period temperature, dissolved
inorganic nitrogen and other water variables were routinely
followed according to standard methods (APHA, 1975). The
variable, the method of measurement, and the sampling intervals are
presented in Table 1.3.
29
Table 1.3 Water quality testing.
Variables
thod
Interval
Terperature
TherriDeouple
Hourly
pH
Colorimetric
Weekly
Oxygen
Winkler titration
Weekly
Phosphorus
Anino acid
Weekly
Thrbidity
Absorptanetric
Weekly
Animnia-nitrogen
Nessler izat ion
Weekly
Ni trite-nitrogen
Diazotizat ion
Weekly
Nitrate-nitrogen
cdmiun reduction
Weekly
30
During the experiment tomato leaf samples were taken
from the hydroponic system and greenhouse soil tomato plants for
tissue analysis to determine plant nutritional status. Fish food
was
also
analyzed
for
elemental
composition.
Emission
spectroscopy (Jarrel-Ash model 750 Spectrometer) was used for
analyses and were based on the methods of Chaplin and Dixon (1974).
The
following elements were tested:
Nitrogen, Phosphorous,
Potassium, Calcium, Magnesium, Manganese, Iron, Copper, Boron,
Zinc, Aluminum.
31
RESULTS
Table 1.4 presents the fish growth and harvest data. A
total of 42.18 kg of fish was harvested during the 7 1/2 month test
period. At the August 24 sampling and harvest it was apparent
that tilapia were present in two size classes. About one-half of
these fish had reached harvestable size while the other half were
still quite small. The edible sized tilapia were harvested and the
remainder returned. Tilapia fry were observed in large quantities
during sampling.
The catfish reached harvestable size in 7 1/2
months. The catfish were healthy and of uniform size.
At the August 24 fish crowd the sex of all of the
mossambica was determined by examination of the genital papilla
according to the method reported by Lowe (1955) and Hepher and
Pruginin (1981).
Sex was confirmed at harvest through dissection
and identification of sex organs. Ninety one percent of the tilapia
harvested on August 24 were male (Table 1.5).
Table
1.6
presents
loading
and
carrying
capacity
coefficients for the combined weights of tilapia and channel
catfish. The maximum loading coefficients occurred at the August
24 and November 18 crowd and harvest. At these loading rates the
water quality remained high. Both the trickling filter and
hydroponic system contributed significantly to the high water
quality.
Figures 1.6 and 1.7 present the results of water testing at
the trickling filter inflow, filter outflow, and hydroponic outflow.
The hydroponic system was removed after the August 23 tomato
harvest. After this, water samples were taken at the filter inflow
32
Table 1.4.
1982 Fish stocking, harvest weights and specific growth
rates.
Mean Wt.
Date and Event
4/1 (Stocking)
4/1 (Stocking)
Fish
Tilapia**
Catfish***
Nurber
(n)
120
6/2
6/2
(Weigh)
120
(Weigh)
Tilapia
Catfish
8/24
8/24
8/24
8/24
(Harvest)
(Return)
(Harvest)
(Return)
Tilapia
Tilapia
Catfish
Catfish
59
(weigh)
10/11 (weigh)
Tilapia
61
catfish
57
11/18 (Harvest)
11/18 (Harvest)
Tilapia
Catfish
61
io,ii
60
60
61
3
57
57
*SGR = Specific Growth Rate
**Tjlapla = Ti1a
mossambica
***Catfjsh = Ictalurus Runctatus
Total
SGR*
(%/day)
9.1
12.8
(kg)
1.09
0.77
31.9
42.8
3.83
2.57
1.99
1.92
298.5
68.9
139.1
127.2
12.30
4.20
0.42
7.25
2.26
0.93
1.42
1.31
115.5
223.3
7.05
12.73
1.08
1.17
170.2
334.7
10.38
19.08
1.02
1.07
33
Table
1.5.
Percent male and female Tilapia mossambica.
Event
No. Males
No. Fles
%Males
%Farles
Harvested
(8/24)
54
5
91
9
Returned
(8/24)
9
52
15
85
Table 1.6.
Loading and carrying capacity factors for combined T. mossambica and I.
punctatus weights.
Loading
Carrying
capacity
(kg/i-mm)
Weight per
biofilter
Weight per
hydroponic
Weight per
surfae
surfae
plant
(kg/rn )
(kg/rn )
(kg
tcnto
Weight
densiy
Date and Event
(kg)
(kg/rn )
4/1 Stocking
1.86
0.29
0.08
0.10
1.13
0.08
6/2 Crowd
6.40
0.99
0.26
0.33
3.88
0.27
8/24 Crowd & Harvest
24.17
3.76
1.00
1.23
14.65
1.01
10/li Crowd
19.78
3.07
0.82
1.01
11/18 Harvest
29.46
4.59
1.22
1.50
L)
Figure 1.6.
Nitrate, Nitrite, Ammonia and pH values. Hydroponic system removed
after 8/23.
7.,
7.2
t'ThtI.IIal.tlJIatIaIl uitkIIIIIIiiIg
k.O
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0.3
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....iiiIkhi &hiIigIIiIIi
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'fl
513
/1O
3/77
3/2'
3/31
0/7
6/14
1./21
6/29
7/3
7/12
7/19
7/21.
9/7
/
$/j
1/23
9/37 9/10
9/77
9/24
9/30
7017
10/7k l2I
I1'. Il4 I7!II I7II
Figure 1.6
L)
Figure
Water temperature, turbidity, phosphate,
Hydroponic system removed after 8/23.
1.7.
and
oxygen
values.
co
SCflDIIUI
JULY
JUlY
$AY
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Ill
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2011
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$124 1117
$110
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0/23
$114
$11
0/2
7124
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39
and outifow until the final fish harvest on November 18.
The pH of the water remained very stable throughout
the experiment. While the hydroponic troughs were in place the
pH:
measured pH ranged from a low of 6.5 to a high of 7.2.
After the
hydroponic troughs were removed the pH range increased from a low
of 6.6 to a high of 76.
Ammonia:
The ammonia values represent total ammonia
(NH + NH -N). Ammonia slowly increased in the water during the
3
4
experiment. The filter pallets in the trickling filter were
effective in harboring nitrifying bacteria as the effluent ammonia
values were lower than the filter influent values. The hydroponic
system also removed ammonia.
After the hydroponic troughs were
removed there was no substantial increase in ammonia and the
trickling filter outflow continued to be lower than the inflow. The
highest ammonia value recorded was 1.3 ppm.
At the pH of 6.8 and
temperature of 27°C this meant that 0.008 ppm existed as unionized ammonia (NH-N). Even at the higher pH values unionized ammonia never went above 0.016 ppm.
Nitrite: The nitrite content of the water remained very
low and ranged from a low of 0.01 to a high of 0.13 ppm. There was
no clear pattern through the trickling filter. In some instances
the filter effluent was higher than the influent and opposite other
times. There was a reduction of nitrite at the hydroponic outflow.
Nitrate: The nitrate content of the water increased
during the experiment, and jumped rapidily after the hydroponic
troughs were removed. There was an increase in nitrate as the
water exited the trickling filter and a decrease in nitrate as the
40
water exited the hydroponic troughs.
Oxygen:
The lowest dissolved oxygen measured in the
fish culture tank was 4 ppm. The pallet configuration in the
trickling filter was effective in aerating the water as the filter
effluent was usually higher in oxygen than the influent. Oxygen
was consumed as it passed through the hydroponic system.
Phosphate:
The phosphate content of the water increased
during the experiment. In some instances there was an increase in
phosphate as the water left the trickling filter. There was a
decrease in phosphate as the water passed through the hydroponic
system.
Turbidity:
Water turbidity remained low
while the
hydroponic system was in use and rose rapidly after the hydroponic
system was removed. A phytoplankton bloom occurred shortly
after the hydroponic system was removed which could account for
the high turbidity levels. The settling tank at the base of the
trickling filter had only a moderate effect on removing particles
and in some instances there was an increase in turbidity at the
filter outflow. Initially the hydroponic system did not have an
effect on turbidity levels, but as the plants matured and their root
masses developed, turbidity began to drop as water exited the
hydroponic troughs.
Temperature: Daily high and low water temperatures are
presented in Figure I.?. The greenhouse was effective in
maintaining high water temperatures throughout most of the test
period. During the testing period the highest temperature
recorded was 30°C in August and the lowest was 13°C in April.
41
Hydroponics:
Initial hydroponic designs
I
tried failed
because of root rot. This was caused by using a gravel growing
medium. The first medium tested was pea gravel (3-7 mm
diameter). Plants grew vigorously at first but by maturity they
wilted severely and died.
I observed that the roots had grown so
tightly around the pea gravel that they acted like a dam and blocked
waterfiow. Adequate oxygen could not get to the roots and they
suffocated. The pea gravel was tried again with the recirculating
pump set on a timer to allow water to drain from the hydroponic
troughs and aerate roots. This was unsuccessful also because the
tomato roots again blocked water flow and prevented the water
from draining. This resulted in root suffocation and leaf wilt.
The pea gravel was replaced with a larger diameter
volcanic pumice (10-20 mm diameter). I anticipated that the large
diameter rock would create enough void space to prevent clogging.
A planting of tomatoes and European cucumbers again showed rapid
and healthy growth but by the time the plants reached maturity the
roots blocked water flow and the plants began to wilt as the roots
suffocated.
The design that was succesful was a modification of a
recent hydroponic development known as the Nutrient Film
Technique (NFT) (Cooper, 1975). This design does not use any
growing medium but instead a shallow stream of nutrient water is
constantly recirculated through the lower surface of a dense mat of
plant roots. The upper surface of the root mat remains exposed to
moist air. This provides both abundant water and oxygen to the
roots and eliminates the need for a drain-down phase.
42
Table 1.7 compares first bloom, first harvest, and average
yield between the hydroponic and greenhouse soil tomatoes.
Tomatoes grown in the hydroponic system and irrigated with only
water from the fish culture tank bloomed 15 days before the
tomatoes in the soil beds. Tomatoes were first harvested in the
hydroponic system in mid-June and the first harvest of tomatoes in
the soil beds was 12 days later. The average tomato yield, by
weight, of the hydroponic plants was significantly greater (p
0.05) than the average tomato yield from greenhouse soil beds.
Table 1.8 presents a nutritional profile of leaf tissue
analysis from the hydroponic troughs and soil beds, fish pellets, and
literature values for deficient, sufficient and excessive amounts of
tissue element.
Leaf samples from the hydroponic system were taken at the
head of the trough (inflow) and exit (outflow). At the June 7
sampling tomato plants near the hydroponic inflow were deficient in
potassium and magnesium and tomato plants near the hydroponic
outflow were deficient in potassium.
At the July 2 sampling the
tomato plants near the hydroponic outflow were deficient
potassium and zinc.
in
Analyses of leaf samples from tomatoes grown
in the soil beds showed that the tomato plants were deficient in
potassium and calcium at the June 7 sampling and deficient in
calcium at the July 2 sampling (Table 1.8).
The nitrogen content of the fish food, fish, tomato plants
and fruit, and sludge is presented in Table 1.9. The nitrogen
partitioning among the different biological components is presented
in Table 1.10. These values were calculated from cumulative
43
Table 1.7. Tomato yield from the greenhouse hydroponic and
soil systems.
Greenhouse tate
Late
No.
First First
Final Yield/Plant
Transplant Plants Bloan Harvest Harvest
(kg)
Location
Sown
Hydroponic
2/17
4/1
24
5/14
6/18
8/24
4.1 + 0.9*
Soil
2/17
4/1
10
5/29
6/30
8/24
3.2 + 0.4*
*
Using the Student's t-test the mean tomato yields of the
hydroponic and greenhouse soil beds were statistically different at
p >0.05.
Table 1.8
Nutritional content of soil-grown and hydroponic-grown
tomato leaves, and
fish pellets, plus literature values for deficient, sufficient and excessive
amounts of
tissue elements.
Source
Lte
percent
N
P
K
Ca
parts per million
r.t
Fe
Cu
B
Zn
Al
NF1' Leaves Inflow (6/7)
4.82
1.21
2.49
1.26
0.42
55
99
13
36
55
0
NF1' Leaves Outflow (6/7)
4.70
0.74
1.50
2.09
0.53
63
147
10
31
34
120
Soil Leaves
(6/7)
5.05
1.01
2.49
0.74
0.58
42
123
8
28
29
0
NET Leaves Inflow
(7/2)
5.18
1.14
3.82
3.10
0.45
88
74
12
34
56
16
NET Leaves Outflow (7/2)
4.58
0.84
2.42
2.98
0.48
41
61
8
32
14
29
Soil Leaves
5.09
1.14
3.94
0.80
0.60
40
102
10
38
34
0
6.90
0.79
1.23
2.37
0.30
140
220
15
21
192
120
0.19
3.40
0.90
0.42
4
24
25
0.20
3.50
0.91
0.43
5
30
30
(7/2)
Fish Food*
Deficient**
Sufficient**
Excess**
*purjna Trout Chowtm
3.50
>1.51 >6.10 >6.0
30
30
>0.87 >400 >300
>100
**Reported for greenhouse tomato leaves (Bauerle, 1975; Jones, 1975).
<500
>150 >500
45
Table 1.9.
Nitrogen content as percent of dry weight.
Source
Fish P00,1*
% Nitrogen (mean ±. 95% C.L.J
6.51 ± 0.30
Fish
T.nxssanbica
I. punctatus
10.81
10.27
+
+
1.19
1.07
Tcniato Fruit
1.98
+
0.53
Tczto Leaf
5.57
+
0.74
Taito Stan
1.94
-F
0.95
Tarto Roots
3.66
-F
0.44
Sludge
4.26
*purjna Trout Chow
0.31
I
46
Table 1.10.
Nitrogen balance in a closed recirculating system for
the culture of tilapia, channel catfish, and hydroponic tomatoes.
Orgin
Nitrogen(n)
Percent of Input (%)
Nitrogen Input:
Fish Food*
1,844
Nitrogen Output:
Fish Nitrogen
Tilapia**
Catfish***
360.0
11.8
19.5
0.6
Leaves and sterns
Roots
154.9
283.3
64.0
15.4
3.5
Sludge Nitrogen
Suspended solids
60.1
3.3
2.0
0.1
23.1
0.1
959.3
52.0
123.1
200.8
6.7
10.9
1.7
0.1
8.7
0.4
67.6
0.5
402.3
21.9
481.3
26.1
Tcrriato Nitrogen
Fruit
8.4
Dissolved
NH3-N
2N
ND3-N
Total
1.2
Nitrogen Ramming in Tank
Fish Nitrogen
Tilapia
Catfish
Suspended Solids
Dissolved
NH3_N
2N
3-N
Total
Unaccounted Nitrogen
*purjna Trout Chowtm
**Tjlapja nssantica
***Jctalurus punctatus
3.7
47
tomato harvests, cumulative sludge draining, and fish weights and
water quality on August 23.
The nitrogen in the fish comprised 37.7% and the tomatoes
(plant and fruit) comprised 27.3% of the nitrogen input.
The
amount of nitrogen removed in the sludge draining accounted for
4.6%, and the nitrogen (other than fish) remaining in the tank
accounted for 4.3% of the nitrogen input.
Using this mass balance
method 26.1% of the nitrogen input could not be accounted for.
DISCUSSION
Integrating hydroponics to a recirculating aquaculture
system is
an effective way of removing waste nitrogen and
increasing crop diversification. The combined fish and tomato
plants accounted for 65% of the nitrogen input. Of the waste
nitrogen (not incorporated into fish flesh) the hydroponic system
removed 44% and the sedimentation tanks removed 7.4%.
Sludge drainage removed only a small fraction of the waste
nitrogen.
Because of the low density of fish waste particles,
gravity settling basins should have a retention time of 15 to 60
minutes (Mao et al., 1972; Lomax, 1976).
The retention time in this
study, however, was less than five minutes.
Even long retention times may not be adequate in intensive
fish systems. Chesness et al. (1975b) found that only 6% of the
organic solids could be removed in model sedimentation basins used
on wastewater from catfish culture. This percentage could be
decreased by the addition of alum and other flocculating agents, but
the amount of agent required made the process uneconomical
(Chesness et al., 1975).
Nitrogen that could not be accounted for made up 26.1% of
the total nitrogen input. This nitrogen may have been sequestered
in forms that were not measured such as:
1.
Dissolved organic nitrogen;
2. Denitrification in anaerobic zones;
3.
Volatilization of gaseous ammonia on passage
through
the trickling filter tower;
4.
Waste products remaining on the bottom of the fish
49
tank;
5.
6.
Attached algae along the sides of the tank; and
Material trapped in the trickling filter towers.
This experiment demonstrated the size disparity that can
develop between male and female tilapia. Because females can
begin breeding at an age of 2-3 months and a weight of only 2.5 gms
(Chimits, 1955) energy is directed toward gonad development rather
than growth. In order to achieve market weight in a short period
of time monosex culture of male tilapias is desirable. Sexing of
tilapia can only be done reliably when the fish have reached a size
of 50-70 g (Hepher and Pruginin, 1981).
Other techniques that are
used to control sex are:
1. Monosex culture by hybridization (Hickling, 1960;
Avault and Shell, 1968);
2.
Use of predator species to consume young tilapia
(Hickling, 1962; Meschkat, 1968);
of sex hormones
3.
Use
4.
Sterilization using chemical sterilants, x-rays and
to produce monosex males
(Guerrero, 1975; Shelton et al., 1981);
gamma rays (Al Daham, 1970);
Floating cage culture to prevent egg fertilization by
male sperm (Pagan-Font, 1975); and
5.
6.
Use of species which spawn at an older age such as T.
nilotica and T. aurea (Hepher and Pruginin, 1981).
Hybridization and androgen sex reversal appear to hold the
most promise in producing all male tilapia populations. The
channel catfish did not exhibit this sexual size disparity and their
50
size was fairly uniform at harvest.
Water quality remained well within safe limits for the two
species of fish cultured. Both the trickling filter and the
hydroponic system were important in reconditioning the water.
Ammonia and urea are the primary nitrogenous compounds
excreted by fish. Urea is quickly converted to ammonia and carbon
dioxide by bacteria. The unionized state of ammonia (NH3) is
considered toxic to fish and its concentration is dependent on total
ammonia, pH, and temperature (Downing and Merkins, 1955; Emerson
et al., 1975).
Robinette (1976) established that sublethal effects
of NH occur at 0.12 ppm. The highest unionized ammonia value
recorded during the test period was 0.016 ppm which was well below
the sublethal level.
During the test period measured nitrite in the water did
not go above 0.15 ppm, which is below the toxic levels of 7-13 ppm
for warm water fish (Colt and Tchobanoglous, 1976). The trickling
filter was already conditioned when the experiment began so there
was not the initial nitrite surge at the beginning of the test period
as is often reported for new system start ups.
Nitrate is toxic to fish only in very high concentrations.
Although nitrate levels in the fish culture tank began to accumulate
after the hydroponic troughs were removed they did not approach
the lethal level of 1,400 ppm (Colt and Tchobanoglous, 1976).
Stressful levels of nitrate for warm water fish have not yet been
established.
For optimum growth of warm water fish oxygen levels
should be maintained above 4 ppm (Boyd, 1979).
The oxygen level
51
in the tank measured 4 ppm only once. The trickling filter pallet
design was effective in aerating the water by creating a splashing
action similar to a waterfall. The pallet spacing was adequate to
prevent clogging by materials from the fish tank or bridging of
bacterial populations within the filter towers. Oxygen in the
water was consumed in its passage through the hydroponic troughs.
This was presumably caused by heterotrophic bacterial respiration.
Only 25 percent of the water leaving the filter towers passed
through the hydroponic troughs and the majority of aerated water
from the filter towers was shunted directly to the aquaculture tank.
This design helped to maintain adequate oxygen levels for the fish.
Phosphate is not harmful to fish, but is often considered to
be the element that most frequently limits productivity in aquatic
ecosystems (Boyd, 1979).
Although phosphate was removed by the
hydroponic system the overall effects of the trickling filter on
phosphate levels was not apparent.
In some instances there were
increases in phosphate at the filter effluent. Work done by the
Environmental Protection Agency indicates that flocculation and
settling of organically bound phosphorous in filtration units and
subsequent decomposition may cause an increase in phosphorus
(Anon., 1971).
Locating a recirculating aquaculture system inside a
greenhouse serves a multiple purpose. The heated water acts as
thermal storage for the greenhouse and the greenhouse enables the
water to reach temperatures that promote fish growth. The
optimum temperature for channel catfish and tilapia growth is
between 27-30°C (St. Amant, 1966; Andrews et al. 1972).
Optimum
52
digestion for channel catfish occurs over a temperature range of 2129°C (Shrable et al., 1969). This range was maintained for
approximately 5 1/2 months of the 7 1/2 month testing period.
Apparently the oyster shells above the trickling filter
provided adequate buffering throughout the testing period. The
measured pH ranges were within the optimum ranges for the fish and
plants (Colt et al. 1979; Resh, 1981).
The decrease of elements between leaf tissue samples from
the inflow and outflow tomato plants indicate a progressive
depletion of nutrients along the length of the hydroponic troughs.
The elements that were deficient or borderline deficient were
potassium, magnesium and zinc. Potassium and magnesium were
present in low concentrations in the fish food, but zinc was present
in high concentrations. The low zinc concentrations in the tomato
leaves may have been caused by the zinc complexing with organic
compounds making it unavailable for plant uptake (Maynard, 1979).
The tomato plants exhibited symptoms of potassium and
magnesium deficiency with browning at the tips and chiorotic
mottling of mature leaves. Although the July leaf sampling
indicated a deficiency in zinc, the tomato plants did not exhibit the
symptoms, leaf curl and chlorosis of younger leaves, which are
reported as signs of zinc deficiency (Schwarz, 1975). Chapman
(1966) reported that zinc may not become limiting for tomato plants
until 8 ppm which is lower than the zinc values recorded during this
experiment.
This may explain why the tomato plants did not
display zinc deficiency symptoms during this experiment. Even
with these nutritional limits the average yield of 4.1 kg per tomato
53
plant is slightly higher than the 4 kg commercial greenhouse yields
reported for this variety (Stokes, 1982).
The
successful
Nutrient
hydroponic
Film
Technique
method
(NFT)
was
the most
during
this study.
research has demonstrated that plants raised using the NET can be
employed
grown on much lower nutrient levels than is required in other
hydroponic systems (Hurd, 1978; Windsor and Massey, 1978).
This
is particularly important for hydroponic designs that use only the
relatively low nutrient levels of an aquaculture system.
Other advantages of the NET over traditional gravel
hydroponics are:
Light weight materials can be used, as no growing
medium is required;
1.
2.
No growing medium that needs cleaning and sterilizing
between crops;
3.
Drain-down phase eliminated; and
4. Low capital cost and simplicity.
This study has shown that recirculating aquaculture can be
productively linked to a simple hydroponic design.
Because water
quality stayed at optimum levels during the test period the fish load
could have been substantially increased. This would have provided
more nutrients to the hydroponic plants and reduced the chances of
plant deficiencies. More work is needed to describe further the
most productive combinations of fish and plants in greenhouse
aquaculture and hydroponics.
54
CHAPTER II
AN ENERGY ANALYSIS OF A CLOSED GREENHOUSE
AQUACULTURE AND HYDROPONIC SYSTEM
INTRODUCTION
Aquaculture is often considered to be more efficient than
terrestrial livestock production. Salmonids and catfish can have
food
ratios of 1.0 to 1.5 compared to 2.1 for broiler
chickens and 3.2 for hogs, and 7.7 for cattle (Lovell, 1979).
However, aquaculture is not necessarily efficient from a total
conversion
energy viewpoint.
In intensive systems typical of North American
aquaculture the energy involved in buildings, concrete, fiberglass,
aluminum, pumps, filtration systems, aeraters and high protein
feeds result in energy subsidies of 10 to 60 times the energy
contained in the fish (Edwardson, 1976; Pitcher, 1977; Rawitscher
and Mayer, 1977; Pimentel and Pimentel, 1979). Thus most North
American aquaculture is initially more energy intensive than
competing agricultural systems such as feed lot beef, confinement
hog rearing and broiler chicken production (Pimentel et al., 1975).
The energy picture is even bleaker as the rest of the food system
(processing, transporting, storing, marketing and domestic
preparation) uses about four times more energy than that used in
aquaculture production (Steinhart and Steinhart, 1974).
There is considerablc concern about the sustainability of
such an energy intensive food system. An alternative is an
55
ecological approach that integrates food production systems to
conserve energy, recycle wastes and minimize environmental
impact.
One model to consider is the integration of aquaculture to
solar greenhouse systems. Over 748,000 gardeners used some type
of greenhouse in 1980 (Davies, 1980). Because conventional
greenhouses are energy intensive more gardeners are using solar
greenhouses that use natural means of heating and cooling (Shapiro,
1979).
A common design innovation in solar greenhouses is the use
of large volumes of water for thermal mass. Although water has
proven effective in storing heat and releasing it during cooler
periods it takes up valuable growing space. By integrating heat
storage with food production considerable savings of energy,
nutrient and material resources are possible. For example, the
water used for heat storage can also be used for aquaculture and
this nutrient rich warm water can in turn be used in hydroponic
horticulture.
Aquaculture systems are most often described in economic
or biological terms. An alternate approach is to look at the energy
of an aquaculture system. This can be done either by
comparing the energy contained in the product to the energy
flow
required to produce the product (i.e. energy output/energy input)
or by comparing the energy costs required to produce a unit product
(i.e. energy input/product output) (Welsh and Hopkins, 1982).
The energy output/energy input method allows for the
development of efficiency ratios because both the numerator and
denominator are expressed in the same unit. Comparing different
56
efficiency ratios are meaningful only when they are dimensionless;
otherwise, statements about efficiency can be very misleading
(Odum, 1971).
The energy input/product output method allows for the
consideration of nutritional and other differences among food
products.
For example, less energy is used to provide protein from
field crops such as wheat and corn than from animal protein
(Pimentel et al., 1975), but animal protein is higher in the amino
acids, lipids and vitamins required for human nutrition (Rawitscher
and Mayer, 1977).
This chapter presents an energy analysis of a closed
greenhouse aquaculture and hydroponic system. The analysis will
be used to develop efficiency ratios (energy output/energy input)
and to analyze the energy costs required to raise a unit product
(energy input/product output). These results will be compared to
conventional greenhouse systems and to various fish culture
systems.
57
MATERIALS AND METHODS
Solar Greenhouse:
2
The 32.6 m solar greenhouse was of
A-frame design with its long axis facing east-west and only the
south facing side glazed. Other portions of the greenhouse were
opaque and insulated to reduce heat loss. See Chapter
I
for
greenhouse details (Table 1.1 and Figures 1.1-1.3).
Aquaculture System: The aquaculture system consisted
of a concrete tank (5.5 m x 1.54 m x 0.9 m deep) connected to a
recirculating trickling filter system. The fish tank held 6,435
liters of water and served as heat storage for the solar greenhouse.
The trickling filter consisted of wooden pallets (40.6 cm x 40.6 cm x
38 cm) stacked in two 416 liter steel drum towers. See Chapter I
for trickling filter details (Figure 1.4).
Hydroponic System: Three flat bottomed PVC gutters
connected to the aquaculture filter outflows served as hydroponic
troughs. The top of the troughs were covered with 4-mu black
plastic to keep roots moist and prevent the growth of algae, and
valves at the filter outflow controlled the amount of water flowing
through the hydroponic troughs. See Chapter 1 for hydroponic
details (Figures 1.4 and 1.5).
Energy Inputs: The energy inputs are divided into two
categories: fixed and operational. Fixed inputs include the
embodied energy costs of the materials and labor to construct the
facility while operational inputs include the annual energy costs of
running the facility.
The embodied energy inputs include the energy to extract
the raw materials through the complete manufacturing, fabrication,
'I.
and shipping of the product. This total embodied energy is often
neglected in energy studies and leads to an underestimation of the
energy inputs required to produce different kinds of food and other
products. The total embodied energy values in the materials used
for the greenhouse, aquaculture and hydroponic systems are based
upon values derived from an extensive literature survey.
The energy labor cost to construct the greenhouse was
estimated at 250 Kcal/hr/person.
values
of
200
Kcal/hr/person
This was taken as an average for
by
Leach
(1976),
and
300
Kcal/hr/person by Morehouse and Gross (1979).
The operational energy inputs include the energy costs of
running the facility such as those embodied in fish food, electricity,
and labor to maintain the facility. It was difficult to obtain an
accurate estimate of the energy embodied in the feed used to raise
the fish.
The manufacturing company would not release the
percent composition of the ingredients used to produce the feed nor
would they provide an estimate of their energy costs to produce the
feed. This value was estimated from a study by Pimentel et al.
(1975) who present total energy costs of 2,827 Kcal/kg of pelleted
fish food.
Measurements of electrical use by the recirculating pump
were taken using an amp-meter. For energy comparisons electrical
measurements were converted to Kcal/hr using standard conversion
formulas.
The amount of labor required to maintain the greenhouse
facility was based on five years of experience by the author. The
energy values for maintenance labor were estimated to be the same
as that for construction labor energy (250 Kcal/hr/person).
The fixed and operational energy costs were expressed
annually.
The operational
costs
by
definition fit into this
category because they are incurred during each annual growing
season. The fixed costs were amortized over their estimated
useful life (Table 11.1), and a straight line amortization was chosen
to express the fixed costs on an annual basis.
Energy Outputs:
Unlike conventional greenhouses a solar
greenhouse stores excess solar energy in massive objects (rock,
earth, water, etc.) and releases the heat at night and during cloudy
periods. A properly designed heat storage system can totally
replace the need for supplementary heating which can be the major
operating expense in conventional greenhouse production (Leach,
1976; Badger and Poole, 1979; Rotz et al., 1979; White and Aldrich,
1980).
A greenhouse using water for thermal storage can store and
release large quantities of heat. For example in the water storage
of the solar greenhouse in this study a temperature shift of 1°C
represents 2,000 Kcal of heat energy. To determine the heat
contribution of the water storage system of the greenhouse under
study daily maximum/minimum water temperatures were taken.
These daily temperature shifts were converted to Kcal of energy
using standard conversion formulas.
To develop energy ratios net fish yield was converted to
energy units using data from Mackay (1982) and the hydroponic
vegetable production was converted to energy units using data from
Adams and Richardson (1977).
Table 11.1.
systems.
Useful life of greenhouse, aquaculture, and hydroponic
Cczrponent
Useful life (yrs)
Solar greenhouse
20
Trickling filter
10
Hydroponics
10
61
RESULTS
Energy Inputs
Table 11.2 presents the embodied energy values of the
materials used to construct the solar greenhouse. Tables 11.3 and
11.4 present embodied energy values of the recirculating
aquaculture and hydroponic systems. I was able to obtain
embodied energy values of all the major construction components
except for the fiberglass glazing. An exhaustive literature search
did not
yield the
information and fiberglass manufacturing
companies would not release production information to me. In
place of the fiberglass glazing I used the embodied energy values
for tempered glass, which is a common solar greenhouse glazing
material. Construction labor in man-hours and energy values are
presented in Table 11.5.
Table 11.6 presents the percent energy contribution of the
different stages of greenhouse construction. The concrete
foundation and tanks were a major energy cost and accounted for
over 33 percent of the total materials energy costs. Glazing,
sheathing and insulation materials also had high embodied energy
costs. The labor costs were only 0.7 percent of the total energy
costs for construction.
Table II.? presents the amortized costs of materials and
labor as well as the operating energy costs. After amortization
the major energy costs were for the electricity to run the
recirculating pump and the greenhouse materials energy costs
(Table 11.8).
The operating costs were based on a 9-month growing
62
Table
11.2.
Embodied energy values of greenhouse materials.
Total
Source
Itri
Unit
mu/unit
yd3
2,594,338
5,890
10,464
26,625
24,187
192,235
5,019
34,016
x106
Total
Kca
xlO
8.5 yd3
520 l.f.
10 lb
25 lb
150 lb
10 gal
22.05
3.06
0.31
0.67
3.63
1.92
555.7
77.1
7.8
16.9
91.5
48.4
655 b.f.
25 lb
3.29
0.85
82.9
21.4
550
410
60
420
35
25
ft2
ft2
lb
ft2
ft2
lb
10 lb
4.24
1.90
0.82
3.26
1.74
0.85
1.13
106.8
47.9
20.7
82.2
43.9
21.4
28.5
5.10
7.98
128.6
201.1
17.42
0.74
0.03
0.07
439.0
18.6
0.8
0.68
17.1
Arxunt
used
mu
KJlFI
a
a
a
a
a
b
and TA?E
Ready-mix concrete
Reinforcing Bar
Wire for Re-Bar
Anchor bolts & nuts
Wire mesh (6x6")
l.f.
lb
lb
lb
Asphalt eu.alsion
gal
c
a
Lurber
Nails
b.f.
b
Plywood (1/2")
Masonite (1/8")
Asphalt felt
Roll roofing
Sheet metal flashing
Nails
lb
A1DG
b
a
a
d
a
c
Aluninixn foil
ft2
ft2
lb
ft2
ft2
lb
lb
7,705
4,621
13,630
7,753
49,800
34,016
112,676
ft2
ft2
8,800
44,337
580 ft2
180 ft2
ft2
lb
b.f.
lb
72,570
99,018
5,019
34,016
240 ft2
7.5 lb
6 b.f.
2 lb
34,144
llATKN
b
b
5 1/2" Batt
Polystyrene (2")
AZDG
a
c
e
a
Glass
Caulk
Wood
Nails
c
Wire
lb
d
PAINT
White
gal
1.7
UUCAL
20 lb
437,025
2 gal.
0.87
21.9
71,344
34,144
25 l.f.
5 lb
1.78
0.17
44.9
4.3
84.56
2,131.1
PUM3IIG
b
c
Plastic pipe (3")
Valves
l.f.
lb
(RNL1UFL.L
Hannon et
b Hannon et
c Makhijani
d MeGuiness
a
al., 1976.
al., 1977.
and Lichtenberg, 1972.
et al., 1977.
63
Table 11.3.
Embodied energy values of trickling
filter materials.
Source
It
a
Arrount
Total
Total
B'II.J
Kcal
Unit
BTLJ/unit
used
x106
x104
Steel drirns
lb
16,803
200 lb
3.36
84.7
b
Plastic pipe
lb
46,630
10 lb
0.47
11.8
c
Purp
d
Valves
lb
d
Wood
b.f.
a
Nails
lb
180,000
1
0.18
4.5
34,144
5 lb
0.17
4.3
50 b.f. 0.25
6.3
5,019
34,016
a Hannon et al., 1976.
b Hannon et al., 1977.
c Steinhart and Steinhart, 1974.
d Makhijani and Lichtenberg, 1972.
2 lb
0.07
1.8
4.50
113.4
64
Table 11.4.
Embodied energy values of hydroponic materials.
Total
Total
Bill
used
x106
Kcal
x104
71,344
54 1.1.
3.85
97.1
lb
4,097
2 lb
0.01
0.2
Plastic valve
lb
46,630
1 lb
0.05
1.3
c
Eye bolts
lb
26,625
6 lb
0.16
4.0
c
Guy wire
lb
34,385
7 lb
0.24
6.1
4.31
108.7
Source
Itn
Unit
lmJ/unit
a
PVC pipe
l.f.
b
Plastic sheet
a
a
b
c
Hannon et al., 1977.
Makhijani and Lichtenberg, 1972.
Hannon et al., 1976.
Arn3unt
Table 11.5. Construction labor energy.
Total
Total
iflU
Kcal
x106
x104
Itam
Unit
Amunt
BTIJ/unit* used
Excavation
hr
992
168 hr
0.17
4.3
Concrete forms
hr
992
96 hr
0.10
2.5
Concrete pour
hr
992
16
hr
0.02
0.4
Framing
hr
992
120 hr
0.12
3.0
Sheathing
hr
992
120 hr
0.12
3.0
Finish
hr
992
144 hr
0.14
3.5
Trickling filter
hr
992
24 hr
0.02
0.5
Hydroponics
hr
992
hr
0.01
0.2
0.70
17.4
8
* Energy values taken from Leach, 1976, and Morehouse and
Gross, 1979.
Table 11.6. Percent energy contribution of construction
materials and labor.
Itan
Kcal x
Percent(%)
Foundation & tanks
797.4
33.6
Glazing
460.1
19.4
Sheathing
351.4
14.8
Insulation
329.7
13.9
Trickling filter
113.4
4.8
Hydroponics
108.7
4.6
Framing
104.3
4.4
Other (elect.,paint, pluTbing)
88.2
3.7
Labor
17.4
0.7
2,370.6
100.0
GWU'IUEAL
67
Table 11.7. Amortized energy costs of materials and labor,
and annual operating energy costs.
Jt
Greenhouse & labor
Kcal x
krxrtization
2,147.7
20
Kcal x
Annualized
yrs
107.4
Trickling filter & labor
113.9
10 yrs
11.4
Hydroponics & labor
108.9
10 yrs
10.9
Electricity
117.6
117.6
18.7
18.7
7.0
7.0
Fish feed
Operating labor
QWIT JUFAL
273.0
Table 11.8.
Percent annual energy contribution of
amortized and operating costs.
Itan
Keal x iO4
Percent(%)
Electricity
117.6
43.1
Greenhouse
107.4
39.3
Fish food
18.7
6.8
Trickling filter
11.4
4.2
Hydroponics
10.9
4.0
7.0
2.6
273.0
100.0
Operating labor
cIA'1UFAL
cycle for the aquaculture and hydroponic systems.
Electricity was
calculated for running the recirculating pump continuously during
this time. The pump had a measured amperage of 1.8 or 207 watts.
Running the pump continuously for 9 months required 1,366 Kwatts
or 117 Kcalories of energy. The labor estimate was based on an
average of 1-hour per day to maintain the facility, and to plant and
harvest the hydroponic system, and two fish harvests of 3 hours
each.
The amount of fish food added was based on a production
value of 41.3 kg with a measured food conversion efficiency of 1.6.
Energy Outputs
The
three
energy
outputs
were:
heat,
fish,
and
vegetables.
The 6,435 liters of water in the aquaculture tank
served as heat storage and enabled the greenhouse to operate yearround without the need for supplemental heat. Table 11.9 presents
Reat:
monthly averages of the difference between daily maximum and
minimum water temperature (ST). This LT was converted to
Kcalories to determine the energy contribution of the water system
to the greenhouse heating needs. The average annual heat
contribution was 4.4 x
Fish:
O6
Kcal (Table 11.9).
The fish yield of 42.2 kg for the 1982 production
cycle was used in the energy budget calculations (Table 11.10).
This cycle was chosen because it was the same cycle the hydroponic
data were taken from. To develop energy ratios the fish yield was
converted to energy units using a value of 1.24 Kcal/gm live weight
(MacKay, 1982).
70
Table 11.9.
Average monthly and annual heat contribution
from the greenhouse aquaculture tank.
Avg. Dai1yT
Avg.
Monthly
BTUx1O6
Monthly
KcalxlO4
1.6
1.22
30.72
1.7
1.6
1.11
28.00
2.2
2.5
2.0
1.58
39.86
1.7
1.5
2.3
1.8
1.36
34.29
1.7
2.1
2.2
2.0
2.0
1.58
39.86
Jun
1.8
2.0
2.1
2.1
2.0
1.53
38.57
Jul
2.0
2.1
2.2
2.5
2.2
1.71
43.18
Aug
2.1
1.8
2.0
2.4
2.1
1.67
42.86
Sep
1.9
1.5
3.0
2.6
2.2
1.70
42.86
Oct
1.7
1.8
2.6
1.9
2.0
1.58
39.86
Nov
1.6
1.3
2.4
1.8
1.8
1.36
34.29
Dec
1.2
1.1
1.3
---
1.2
0.97
24.36
17.37
437.92
Month
(°c)
1979
1980
1981
1982
Jan
1.4
1.3
1.8
1.7
Feb
1.6
1.3
1.6
Mar
1.9
1.6
Apr
1.6
May
AT(°C)
71
Table 11.10.
1982 fish stocking and harvest.
Fish
Tilapia nssantica
Ictalurus punctatus
tys to
Avg Wt
Total
(ns)
Harvested Harvest
(gins)
(kg)
120
9.1
120
121-230
189.0
22.7
60
12.8
60
121-230
324.9
19.5
Nurber
Stocked
Avg Wt
Nurrber
72
Hydroponics:
The hydroponic troughs were linked directly
to the recirculating aquaculture system and utilized the nutrient
rich fish-tank water. It required over three seasons to develop a
successful hydroponic design.
The details of this evolution are
presented in Chapter I. The results from this work were that two
tomato crops with similar harvest weights could be produced during
the 9 month fish growing season. One early summer hydroponic
experiment of 1982 yielded a total of 98.4 kg of tomatoes from 24
plants in about 4 1/2 months (see Chapter I Table 1.7). From
previous work with this system I determined that a fall crop of
hydroponic tomatoes with a similar yield as the early summer tomato
harvest can be obtained in the greenhouse.
For the energy budget
calculations the early summer yield was doubled to give a total of
196.8 kg of tomatoes. Tomato yield was converted to Keal using a
value of .20 Kcal/gm fruit (Adams and Richardson, 1977).
Table 11.11 presents the energy output from the
aquaculture and hydroponic systems. The heat output represented
98% of the total energy output with the fish and tomatoes from the
aquaculture/hydroponic systems composing the remaining 2%. The
tank was such an efficient heat collector that the greenhouse never
required supplemental heat during the four year testing period.
Energy Ratios
The energy efficiency ratio was determined using the
following formula:
Energy Efficiency (E.E.) = annual energy output (E0)
annual energy input (E1)
(1)
73
Table 11.11.
Annual energy output and percent contribution
of a closed greenhouse aquaculture and hydroponic system.
It
Kcal x
io
Percent (%)
Heat
437.9
97.9
Fish
5.2
1.2
Taratoes
3.9
0.9
447.0
100.0
EAMY1UFAL
74
Values for the energy input are taken from Table 11.8 and
energy output values are the heat energy, fish and vegetable energy
values taken from Tables 11.7 and 11.11.
A system is a net producer of energy only when the energy
ratio (E.E.) is greater than one. That occurred in this system only
when the heat contribution of the water storage is taken into
account (Table 11.12).
The energy payback was determined using the following
formula:
Energy Payback = initial energy investment
(2)
(annual energy output - annual energy input)
This ratio expresses the number of years to pay back the
investment of construction materials and labor energy. The initial
energy investment will eventually be payed back if the technology's
annual energy outputs exceed its annual energy inputs. After the
payback period the technology will be a net producer of energy.
Table 11.13 presents four methods of determining payback.
The first estimate considers the total energy costs to construct the
greenhouse, aquaculture and hydroponic systems (Table 11.6).
The
annual energy input is the grand total of the Table 11.7 and the
annual energy output is the grand total of Table 11.11. In this
study the greenhouse and aquaculture/hydroponic systems will have
an energy payback of 13.6 years.
When the aquaculture tank is considered just as a heat
storage system the energy payback drops to 6.5 years (Table 11.13).
This is due mainly to a substantial decrease in annual energy inputs
attributed to the aquaculture and hydroponic systems while still
75
Table 11.12.
Energy efficiency ratios (E0/E).
Output
Heat, fish, taitoes
1.64
Heat
1.60
Fish
0.019
Tomatoes
0.014
* E0/E
= Annual energy output (Kcal)/Annual energy input (Keal)
76
Table 11.13.
Energy payback in years.
Output
Energy
Investment
(KcalxlO4)
Annual
Energy Input
(KcalxlO4)
Annual
Energy Output
(KcalxlO4)
Energy
Payback
(years)
Heat, fish, tanatoes
2370.6
273.0
447.0
13.6
Heat
2147.8
107.4
437.9
6.5
Fish
113.9
154.7
5.2
Fish, tcntoes
222.8
165.6
9.1
77
maintaining a high energy output.
When fish and fish plus tomato output are evaluated
without consideration of the heat contribution there would not be
an energy payback (Table 11.13).
Table 11.14 presents different calculations of the energy
required to produce a unit weight of fish or tomato. When the
energy cost of the greenhouse is combined with the aquaculturespecific energy costs it requires 63,462 Kcal of energy to produce a
kg of whole fish. When only the aquaculture specific costs are
considered the value drops to 37,458 Kcal/kg fish.
evaluating the energy costs to produce a kg of
hydroponic tomatoes a consideration of the total annual energy
In
input
(greenhouse + aquaculture + hydroponics) yields a value of
13,872 Kcal/kg tomato. When the hydroponic-specific energy
inputs are considered (aquaculture + hydroponics) this value drops
to 8,415 Kcal/kg tomato.
p1*]
Table 11.14.
or tomato.
Energy required to produce a unit weight of fish
Annual
Food
Energy Input
(kcalxlO4)
Output
(kg)
Kcal/kg
Greenhouse + Aquaculture
262.1
41.3 (fish)
63,462
Aquaculture
154.7
41.3 (fish)
37,458
Greenhouse + Aqua + Hydro
273.0
196.8 (tanatoes)
13,872
Aquaculture + Hydroponics
165.6
196.8 (tcrrtoes)
8,415
Input Ccnponent
79
DISCUSSION
The United States food system is the most productive the
world has ever seen. It is also the most energy intensive system of
all time (The Cornucopia Project, 1981). At the present time
annual fossil fuel consumption is the highest it ever has been and
the United States alone consumes 29% of it (FEA, l967b). Fossil
fuels account for 94% of the total fuels consumed in the United
States (FEA, 1976b).
The epoch of fossil fuel use, as viewed in perspective with
the history of man, will be but a small 'blip' in history; 500-700
years or at most 0.0 01% of the time man has been on earth (Pimentel
and Pimentel, 1979). This is because fossil fuels are nonrenewable resources and very little is being done to conserve the
supply.
A number of studies have highlighted the consequences of
continuing energy intensive systems (Odum, 1971; Meesarovic and
Pestel, 1974; The Cornucopia Project, 1981).
In assessing a technology it is important to determine how
much energy is required to build and operate the technology
relative to the energy, food and other benefits it provides. Fish
farming systems can be looked at in terms of the energy intensity
required to produce a product. Very few comparative studies,
however, have been done of different aquaculture systems. An
exception is a study by Edwardson (1976) comparing the energy
requirements for different types of aquaculture systems. Table
11.15 presents a summary of his findings and includes the amount of
kilocalories required to produce a kilogram of whole fish for the
different aquaculture systems and their energetic output/input
Table 11.15.
systems.
Energy requirements for different aquaculture
Systan
Kcal/kg*
(whole fish) E0/E**
Thailand--carp/tilapia (subsistence)
23.9
51.88
Congo--tilapia (subsistence)
47.8
25.94
El Salvador--tilapia/shrirrp (subsistence)
238.9
5.19
Philippines--milkfish (pens)
477.8
2.59
Taiwan--milkfish (ponds)
1,672.2
0.74
Japan--carp (cages)
4,300.1
0.29
Israel--carp/tilapia (ponds)
6,450.0
0.19
UK--trout (ponds)
13,377.9
0.093
Germany--carp (ponds)
18,155.8
0.068
US--catfish (ponds)
22,933.6
0.054
Japan--carp (recirculation)
73,817.5
0.017
* Values from Edwardson, 1976.
** E0/E1 = Annual energy output (Kcal)/Annual energy input (Keal)
ratios, or energy efficiencies.
As Table 11.15 table indicates most of the subsistence fish
farms are very energy efficient. In these systems human labor
rather than motors and other equipment produce the work and fish
that utilize a short biological food chain are reared. Most of the
freshwater and brackish water fish of Asia fall into this category.
The most common fish reared are herbivorous and omnivorous
species such as carp, milkfish, and tilapia which feed on natural
vegetation and aquatic organisms.
Energy intensity increases with the practice of
supplementary feed, pumping and aerating water, and other
equipment and building uses.
This demands a higher energy price
which is exacted through the use of fossil fuel subsidies.
In
Edwardson's analysis as the degree of intensity increased there was
a concomitant increase in the amount of feed, fuel and equipment
used to produce a kg of fish.
Edwardson's
data
provide
valuable
comparative
information, but his energy calculations do not include total
embodied energy--the total energy demand attributable to a
product including all the steps from extraction of raw materials to
the final fabrication, delivery, operation and maintenance. This
would not affect the subsistence fish farming values as much as the
energy and equipment intensive fish farming practices. If
embodied energy was included in Edwardson's calculations the more
intensive fish farming practices would have even bleaker energy
ratios.
The energy
values of the
greenhouse aguaculture and
sM
hydroponic system I studied can be viewed in a number of ways.
Because the water system in the greenhouse is used for three
purposes-- heat storage, aquaculture, and hydroponics--the energy
ratios can be viewed separately and together. When combining the
energy outputs of the heat storage, fish and hydroponic systems the
energy ratio is an efficient 1.64 which is between the Philippines
and Taiwan milkfish operations of Table 11.15. If the water was to
be used just for aquaculture without considering the heat
production or hydroponic vegetable production the ratio of 0.019 is
close to the value of 0.017 that Edwardson reports for an intensive
water recirculating aquaculture system.
Only when the greenhouse aquaculture system is used in an
integrative manner does the energetics look favorable. This is due
to the design of the greenhouse system, which makes the
aquaculture component an efficient heat collector as well.
Conventional all-glass greenhouses normally rely on fossil
fuels to supply the heat required for optimum plant growth. Leach
(1976) performed a study of the energetics of conventional all glass
lettuce producing greenhouses and determined that they had energy
efficiency ratios between 0.0023 to 0.0017. The energy cost of
fuel for heating accounted for over 80% of the input energy costs.
The hydroponic vegetable producing system I studied was an order
of magnitude more efficient than the Leach (1976) study.
Strictly in terms of energy output, the food produced in
solar greenhouse can almost be ignored.
a
Even if there were a total
crop failure the greenhouse would still show a large annual energy
surplus. This analysis points up one of the short-comings of net
energy analyses:
The most important properties of a commodity
are sometimes poorly correlated with the commodity's embodied
energy and the commodity's apparent value is distorted by the net
energy analysis.
For example, fish and tomatoes are eaten primarily not for
their energy content, but for their minerals, vitamins, fiber and for
the variety they add to the diet.
In addition, from a monetary
basis the potential yield of the aquaculture and hydroponic systems
would be worth several times as much as the value of the heat.
Assuming a dress-out percentage of 60% and a price of $4.40 per kg
the value of the fish yield would be $109.30. Assuming a price of
$1.32 per kg for the tomatoes would give a value of $259.78 for a
total annual value of fish and tomatoes of $369.08.
Using a natural gas price of $6.20 per million BTU and
assuming a 60% furnace efficiency the annual value of the surplus
heat from the aquaculture tank would be $150.77. If electric heat
were used instead of natural gas the electrical cost of $ 0.0347 per
KW or $10.18 per million BTU would yield an annual value of $176.83
from the aquaculture tank.
Labor had the lowest energy requirements in both the
building and operating categories (see Tables 11.6 and 11.8), but the
labor cost may be significant when translated into time
requirements.
For example,
87
eight-hour person days were
required to construct the greenhouse facility and 7 hours per week
were required to operate the facility. These time requirements
may present significant obstacles to theimplementation of smallscale greenhouse aquaculture systems.
CHAPTER III
GROWTH RESPONSES OF TILAPIA MOSSAMBICA FED
COMBINATIONS OF AZOLLA, WATER HYACINTH,
AND EARTHWORM MEAL
INTRODUCTION
The cost of feeding fish can account for over 50% of the
operating expense in aquaculture practices (Hastings, 1969;
Goldman and Ryther, 1975; Burke and Waidrop, 1978).
This high
cost is due to high energy costs in catching the fish for fish meal,
growing the cereal and other crops, and preparing and transporting
the feeds.
One way to reduce this high energy cost is to raise fish
that feed low on the food chain and can utilize plant protein in diet
formulations.
Tilapia are herbivorous fish capable of converting
inexpensive plant food into flesh (Kirinlenki and Mel'nikiv, 1969;
Bayne et al., 1976; Jackson et al., 1982).
Most of the nutritional studies on tilapia have been
concerned with supplementary feeding in outdoor ponds (Stickney
and Hesby, 1977; Collis and Smitherman, 1978; Miller, 1979). From
these studies it is impossible to state how efficiently the feeds
were in directly promoting growth and how much indirectly by
raising the primary productivity of the ponds.
A recent study evaluated some plant proteins in complete
diets for Tilapia mossambica (Jackson et al., 1982). They
evaluated copra, peanut, soya, sunflower, rapeseed, cottonseed,
and leucauna meals with a control diet (30% protein) containing fish
meal. All the diets containing 100% plant protein produced lower
growth rates than the controls. This was attributed to low
methionine and possible plant toxins.
Wu and Jan (1977) reported that specific growth rates of
Tilapia aurea fed on an all peanut protein diet were 58% worse than
on a fish meal control. They also suggested the poor performance
of the peanut was due to the amino acid profile.
Davis and Stickney (1978) reported a 32% decrease in
growth rate with soybean as the protein source instead of fish meal
when fed to Tilapia aurea, and Wu and Yan (1977) recorded a 27%
decrease under similar conditions.
Only a few studies report on the use of the free floating
water ferns (Azolla spp.) or the water hyacinth (Eichhornia
crassipes) as sources of plant protein for animal diets. These
aquatic plants are produced in many natural and impounded waters
and frequently interfere with beneficial uses of water to such an
extent that control measures are often necessary. In view of the
problems associated with the control of these aquatic plants and the
worldwide need for additional sources of food, research to evaluate
their uses as protein sources is important.
Azolla offers potential as a feed ingredient because of its
fast growth rate and high nutritive value. Tally et al. (1977)
reported yields of 980 kg/ha dry weight for Azolla mexicana which
represents about 45 kg N/ha. Because of a symbiotic relationship
with a
nitrogen-fixing
blue-green alga, Anabeana azollae, Azolla is
high in nitrogen and is a potentially attractive source of protein for
animal diets (Bukingham et al., 1978). Azolla plants have been
used as feed for pigs and ducks in Indochina; for cattle, fish, and
poultry in Vietnam and India; and for pigs in Singapore and Formosa
(Moore,
1969;
Subudhi
and
Singh,
1978).
Lasher
(1977)
demonstrated that Tilapia mossambica always consumed Azolla and
Lemna first when these plants were provided in any combination
with 12 other plants. Lasher used fresh plants and did not record
growth rates. There are no published reports on the use of dried
and pelleted Azolla as a potential replacement for or supplement
to commercial fish feed.
Water hyacinth (Eichhornia crassipes) is a vascular
aquatic plant that has a tremendous growth rate. Stands of 43,000
kg wet weight of water hyacinth per hectare and weight gains of 4.8
percent per day have been measured (Knipling et al., 1970).
When
grown on sewage effluent growth rates of 800 kg of dry matter per
hectare per day have been recorded (Wolverton and McDonald,
1976).
Most of the work on the use of water hyacinth as an
animal
feed
has
been
livestock. Despite promising
beginnings, many attempts to feed water hyacinths to animals have
failed. The failure has been attributed to the high moisture
with
content and high mineral content (Little, 1968).
The high mineral
content is reduced when the roots are removed and more recent
work with dewatered and non-root hyacinth silage as a supplement
to livestock feed has been encouraging (Baldwin et al., 1974; Easley
and Shirley, 1974; Baldwin et al., 1975; Chavez et al., 1975). There
[PA
are no published reports on the use of dried and pelleted water
hyacinth as a potential fish diet.
Methionine and lysine are often considered the limiting
amino acids in plant protein fish diets (Nose, 1979; Jackson et al.,
1982; Jackson and Capper, 1982). Earthworms can be a valuable
addition to fish diets that are primarily based on plant protein as
they are high in the essential amino acids required for good fish
growth
(Sabine,
1978).
In
addition,
earthworms
can
be
a
significant means of recovering large amounts of protein that are
currently lost or wasted in intensive agricultural and food
industries and they are easy to raise on a small scale. There is
only one reported use of earthworms as a component of tilapia diets
(McLarney and Parkin, 1981). These researchers supplemented
commercial diets with additions of live earthworms on tests using
the blue tilapia (Ti1ap aurea). They found that the growth rate
of tilapia was reduced with increased replacement of commercial
pellets by earthworms. These researchers did not test what effect
earthworm additions would have on all-plant diets.
The purpose of this study was to determine the growth
response of Ti1a2J mossambica fed an all plant protein diet; a plant
protein diet supplemented with earthworms; and combinations of
these diets as a supplement to a commerical diet.
MATERIALS AND METHODS
Tilapia mossambica were used for the feeding trials.
Ingredients for the experimental diets consisted of: Azolla (.
mexieana), water hyacinth (Eichhornia erassipes), and earthworms
(Eisenia foetida). A commercial catfish pellet served as the
control diet. Table 111.1 presents the percent composition of the
diets.
test diets were pelleted for ease of handling,
preservation, and optimum food conversion. Pelleted diets were
made in the following manner:
The
1.
The food ingredients were thoroughly mixed and passed
through a hand operated grinder fitted with a 4.75 mm sieve.
2.
The ground mixture was spread on trays in thin layers
and dried in a solar drier until they held a shape when gently
pressed together.
3.
again.
The mixture was passed through the grinder and sieve
It came out in long spaghetti-like strands that were broken
into 3-5 mm long pellets by hand.
4.
The pellets were spread onto trays and allowed to dry
completely.
5.
The dried pellets were stored at -20°C until used in
feeding trials.
Proximate analysis
(protein, ash, lipid, fiber) was
determined for the test diets and the control, Purina catfish chow
(Table 111.2). Analyses were conducted according to official
lM
methods
of
analysis
(AOAC,
1975).
Nitrogen
content was
determined by macro-Kjeldahl and crude protein was calculated as
Table 111.1.
Trial No
Diet
A
1
2
3
%Water Hyacinth
---
100
---
D
100
90
---
-------
-------
100
E
F
G
H
K
L
M
N
0
P
Q
%Worm%Camrcial
100
C
J
5
%Azolla
B
I
4
Percent composition of test diets.
---
100
10
100
90
10
---
---
100
-------
25
50
100
100
75
50
---
-----
100
67.5
45
-------
---
7.5
5
25
50
100
Table 111.2.
Proximate analysis of tilapia test diets.
Diet
lOO?6Azolla
lOO96Hyacinth
9096 Azolla/l096Worm
9096 Hyacinth/1096 Worm
Ccnmercial*
*purjna catfish chow
Protein
31.2
25.4
34.1
29.1
31.0
Lipid
4.5
2.2
4.9
2.9
8.6
Ash
Fibe
12.0
20.0
11.8
18.5
11.1
18.3
10.1
16.4
9.3
io.o
91
Kjeldahl nitrogen x 6.25 (AOAC, 1975). Ash was determined as
residue after heating at 600°C for four hours (AOAC, 1975). Lipid
was determined by soxhiet ether extraction and fiber was
determined using the acid-detergent method (A0Ac, 1975).
Table
111.3 presents recommended nutritional levels for tilapia diets.
Polyethylene tanks holding 190 liters (0.71 m high x 0.57 m
wide) were used during the feeding trials.
Each tank was fitted
with subgravel filters made from clay flower pots (127.8 cm wide x
22.9 cm high). A plastic disc with slots cut in the face was placed
on the bottom of the pot and the edges and drain hole were sealed
with silicone sealant. An airline was connected to the disc and the
pot was filled with pumice rock and crushed oyster shell (Figure
111.1).
Silent Gianttm aquarium air pumps were used to power the
subgravel filters. One air pump was used for two tanks. The
filters were cleaned every two weeks and approximately 13 liters of
water were siphoned from the bottom of each tank weekly. The
temperature in all the experimental tanks was maintained at
26.5°C±1°C by 150 watt submersible heaters.
Each diet was replicated three times during a feeding trial
and each tank contained 15 fish. The fish were fed 3% of their
body weight twice daily. A subsample of fish was netted from each
tank every two weeks to check weight gain for feeding rate
adjustments. Water temperatures were taken daily and tests of
water chemisty (dissolved oxygen, ammonia, pH) were performed
weekly. Dissolved oxygen was tested using the Winkler titration
method,
ammonia by nesslerization, and pH colormetrically.
A
Hach DR/2 spectrophotometer was used to measure ammonia and pH.
92
Table 111.3.
Nutritional requirements of tilapia.
Nutrient
Protein*
Carbohydrate**
Lipid**
Fiber**
*Cruz and Laudencia, 1977
Davis and Stickney, 1978
Jackson, et al, 1982
Jauncey, 1982
Mazid, et al., 1979
National Research Council, 1977
Newman, et al. 1979
**Natjonal Research Council, 1977
Effective Levels
In Diets (%)
2040
15-30
10-15
10 or less
93
Figure 111.1.
Tanks (190 liter), filter, and aeration system used
for feeding trials.
94
view:
Figure 111.1
ter-
tsc
95
Differences in growth responses and water quality were tested
using analysis of variance and Duncan's multiple range test
(Duncan, 1955).
Pellet stability was measured by placing a known weight of
pellets on a fiberglass screen (1 mm mesh) and immersing in water
for 20 minutes. The pellets and screen were then removed, dried
and weighed.
Each diet was replicated five times.
RESULTS
The results of the feeding trials are summarized in table
111.4. Statistical analyses were performed on specific growth
rates (SGR) and water quality within each trial.
In all of the trials tilapia fed a diet composed of 100%
plant protein had a lower SGR than other diets (p>O.05). A 10%
addition of earthworm meal to the Azolla diet (trial 2) resulted in a
SGR that was not significantly different than an all commercial
diet. A 10% addition of earthworm meal to a water hyacinth diet
(trial 3) resulted in a SGR that was significantly greater than an all
water hyacinth diet, but lower than an all commercial diet.
When equal parts of Azolla and a commercial diet were
combined, tilapia did not have as high a SGR as those fed a
commercial diet (trial 4). Tilapia growth rate on a diet composed
of 45% Azolla, 5% earthworm meal, and 50% commercial pellets was
not significantly different than on an all commercial diet (trial 5).
The pH of the water for all the trials remained stable
throughout the experiment.
within acceptable
The pH range of 6.6 to 7.5
limits for tilapia
(Mahdi,
was well
1973).
Lowest
dissolved oxygen values were recorded for the commercial and
water hyacinth treatments. During only one observation did
dissolved oxygen values fall below 4 ppm. All of the other values
were above stressful levels (Mahdi, 1973).
The unionized form of ammonia is considered lethal to fish
(Downing and Merkens, 1955) and its concentration is dependent on
total ammonia, pH, and temperature (Emerson et al., 1975).
In all
of the diets tested unionized ammonia in the water stayed well
Table 111.4.
Specific grth rates and water quality of five feeding trials.
Trial
No.
1
2
3
()
Initial wt.
TreatnEnt
nEan
Final wt.
nan (n)
Survival
(%)
Oxygen (pi)
Amxinia (pp)
(9Wday)
nan (+s.d.)
rIEan (+s.d.)
A
14.2
39.3
60
100
1.708
77 f 068
B
12.0
22.2
60
90
103b
6.9 +
C
18.2
56.0
60
100
187C
55
D
12.1
40.5
65
100
187a
64+138
E
11.3
55.0
65
100
248b
6.2
F
12.5
73.3
65
100
273b
6.4 +
G
19.0
49.9
62
100
1.568
H
20.6
68.7
62
100
I
18.9
78.6
62
J
11.3
31.2
K
12.1
L
05b
+
0.208
0.33
0.21 + 0.138
0.45 +
017b
0250208
rran (+s.d.)
6.9 +
018
7.2 + 0.38
7.1
+
Q38
72+048
038
p.60 +
045b
6.8
178
0.63 +
035b
6.8 + 0.28
6.0 + 2.08
0.37
0208
7.0 4 0.38
193b
58+158
041011a
72+018
100
229c
5.4
56
100
1.798
6.7 + 1.28
0.19 + 0.098
37.7
56
100
202ab
6.2 + 0.8k
0.41
+
033b
7.1 +
11.4
40.3
56
100
224b
6.5 + 1.48
0.30
+
010b
6.8 + 0.48
M
21.3
53.7
56
100
278c
6.0 + 1.58
0.51
040b
6.9 +
N
6.0
13.6
60
100
1.588
6.9 +
Q48
0.46
4.
0168
7.3 + 0.28
0
6.1
25.5
60
100
234b
6.8
+
Q48
0.61
+
035b
7.2 + 0.38
P
6.4
34.4
60
100
278c
6.9 +
10a
0.60 +
041b
7.0 + 0.38
Q
6.1
37.7
60
100
3.Ol
+
6b
0.77 +
036b
6.9 + 0.28
4
5
*
R*
No.
days
Specific Growth
±
±
O7
4
041b
0.72
Rate
abCyaiues with the sai
superscripts within each trial are not significantly different (P>0.05).
6.8
01a
f
0.18
6.9 + 0.48
058
within accepted ranges recommended for warm water fish (European
inland Fisheries Advisory Commission, 1973; Robinette, 1976).
Table 111.5 presents the results of the pellet stability
testing. All but the water hyacinth diet were as stable as a
commercial pellet.
Table 111.5.
Mean percent weight loss of pellets immersed in water
20 minutes.
Diet
l06Azolla
l0O Water Hyacinth
9096 Azolla/l096Woims
9096 Water Hyacinth/1096 Worms
Comnercial
Percent Weight Loss
97ao
l4.3c
71a
ll.3
93ab
abcpercent weight loss values with the same superscripts are not
significantly different (P>0.05).
100
DISCUSSION
Five factors that would produce decreased growth rates
using plant proteins in fish diets are:
1.
Toxic
components
such
as
aflatoxins, gossypol,
glucosinolates, anti-trypsin factors (Jackson et al., 1982);
2. Lower
digestibility of plant proteins
and
carbohydrates (Hastings, 1969);
3.
Limiting levels of essential amino acids, particularly
methionine, lysine, and arginine (Nose, 1979; Jackson and Capper,
1982);
Limiting levels of essential lipids (National Research
Council, 1977); and
4.
5.
Limiting levels of vitamins and minerals (National
Research Council, 1977).
There are no reported toxins in either water hyacinth or
Azolla (Wolverton and McDonald, 1976; Buckingham et al., 1978).
The high fiber content of the water hyacinth diet may have affected
its digestibility and contributed to a lower tilapia growth rate.
Table 111.6 presents tilapia requirements for the three most limiting
amino acids found in plant diets (methionine, lysine, arginine), and
amino acid values for Azolla, water hyacinth, and earthworm meal.
Azolla is deficient in methionine, lysine and arginine but
with a 10% addition of earthworm meal the deficiency is corrected.
In the water hyacinth trials both leaves and stolons were included
in the diet formulation. On a dry weight basis the stolon composed
about 25% of the hyacinth diet. This would make the hyacinth diet
deficient in the three amino acids. With the addition of 10%
101
Table 111.6.
Amino acid profiles of methionine, lysine, and
arginine.
Tilapia
Miino acid
Methionine
Lysine
Arginine
requiruint1
Azolla2
0.5396
0.44%
0.44%
0.14%
1.61
1.59
1.51
1.55
1.78
1.64
0.54
0.50
Jackson and Capper, 1982.
2. Buckingham et al., 1978
3. Wolverton and McDonald, 1976.
4. Sabine, 1978.
1.
Water Hyacinth"
Leaf Stolon
Earthworm4
2.18%
4.33
4.13
102
earthworm meal to the hyacinth diet lysine is supplied in abundance
but methionine and arginine remain borderline.
Very little data have been reported on the optimal lipid
levels for warmwater fish and essential fatty acid requirements
have not been specifically identified (Lovell, 1979). Dietary
levels of 5 percent lipid appear to be sufficient for good growth
(National Research Council, 1977). The Azolla test diets were
within this range, but the water hyacinth diets had lipid levels
below 3 percent (Table 111.2). The addition of earthworm meal
only slightly increased lipid levels.
Lipids contain approximately twice as many calories per
gram as do proteins and carbohydrates, and can contribute greatly
to the energy levels of diets even when present in relatively low
quantities (Stickney and Lovell, 1977). Thus, lipids can be used
for maintenance metabolism while protein is freed for utilization in
growth. The higher levels of lipid in the Azolla diet compared to
the water hyacinth diet may have contributed to the better growth
rates of tilapia fed the Azolla diet.
The need for vitamins and minerals
in the
diet of
warmwater fish is well documented (National Research Council,
1977). Fish in natural waters can usually obtain sufficient
amounts of vitamins and minerals by eating food organisms from
their environment, but in intensive fish culture vitamins and
minerals should be supplied in the diet ration (Lovell, 1979).
Because I did not analyze the vitamin and mineral content of the
test diets used in this research I cannot draw conclusions about
adequate or inadequate levels. I did not observe vitamin or
103
mineral deficiency symptoms during the feeding trials, but vitamin
and mineral supplements may be required for long term feeding
success if these test diets are used in intensive fish culture.
Besides
its nutritional
value, Azolla
offers
other
advantages that make it attractive as a feed:
1.
High biomass productivity;
2.
Worldwide distribution;
Vegetative growth habit; and
4. Very little woody tissue.
A major constraint to Azolla cultivation, however, is the
space required for cultivation. Azolla grows as thin layers on the
3.
water surface and therefore a large surface area is needed for
adequate production.
For one year I recorded the yield of Azolla mexicana from
a 3.66 m diameter vinyl-lined pool that held 7,570 liters of water.
Nutrients were supplied to this outdoor pool from the drain-down
water of the greenhouse aquaculture system. The harvest of
Azolla during the active growing season (about 7 months) was 11.9
kg dry weight. In the same size pool, covered with polyethelene,
researchers at the Roda].e Research Center have produced 45 kg of
tilapia (Tilapia aurea) in one season (Strange and Van Gorder,
1981).
A food conversion ratio of 1.5 would require 67.5 kg of feed
to produce this amount of fish.
If 10% of this was supplied in
earthworm meal (6.75 kg) this would still require 61 kg of dry Azolla
which is the equivalent area of five pools (53 m ).
Devoting
this much area to Azolla would only be
-
economical if the Azolla could also be used for other purposes such
104
mineral deficiency symptoms during the feeding trials, but vitamin
and mineral supplements may be required for long term feeding
success if these test diets are used in intensive fish culture.
Besides
its
nutritional value, Azolla
offers
other
advantages that make it attractive as a feed:
1.
High biomass productivity;
2.
Worldwide distribution;
Vegetative growth habit; and
4. Very little woody tissue.
A major constraint to Azolla cultivation, however, is the
space required for cultivation. Azolla grows as thin layers on the
3.
water surface and therefore a large surface area is needed for
adequate production.
For one year I recorded the yield of Azolla mexicana from
a 3.66 m diameter vinyl-lined pool that held 7,570 liters of water.
Nutrients were supplied to this outdoor pool from the drain-down
water of the greenhouse aquaculture system. The harvest of
Azolla during the active growing season (about 7 months) was 11.9
kg dry weight. In the same size pool, covered with polyethylene,
researchers at the Rodale Research Center have produced 45 kg of
tilapia (Tilap aurea) in one season (Strange and Van Gorder,
1981).
A food conversion ratio of 1.5 would require 67.5 kg of feed
to produce this amount of fish. If 10% of this was supplied in
earthworm meal (6.75 kg) this would still require 61 kg of dry Azolla
2
which is the equivalent area of five pools (53 m
Devoting this much area to Azolla would only
be
economical if the Azolla could also be used for other purposes such
105
as wastewater reclamation. Successful uses of aquatic plants for
wastewater aquaculture have been demonstrated by researchers at
Wood's Hole Oceanographic Institute (Goldman et al., 1973;
Huguenin and Ryther, 1974; Ryther et al., 1975; Smith and Huguenin,
1975) and Solar Aquasystems (Serfling and Aisten, 1978; Golueke,
1979; Stewart et al., 1979).
In these designs aquatic plants are
used to remove nutrients from municipal waste water and provide
the base of an aquaculture food chain.
MeLarney and Parkin (1981) determined that earthworms
were less valuable than insects as a supplement or substitute for
commerical feed in tilapia diets. They fed earthworms live and
expressed these weights on a wet weight basis. They noted a
decrease in growth as a commercial diet was increasingly
supplemented with earthworms. In discussing their results the
authors neglected to note that the earthworms were about 80-85%
moisture (Sabine, 1978) and did not correct for this in their data
presentation. Their data can be just as easily interpreted as a
response to the decrease in the total weight of food fed.
Earthworms were a valuable addition to the plant diets I
tested. To produce the amount of worms necessary to make 10% of
the 67.5 kg feed for 45 kg of fish would require 6.75 kg dry weight
or 33.75 kg wet weight of earthworms. I raised earthworms in
wooden bins measuring 2.44 m x 0.91 m x 0.3 m deep. The
earthworms were fed rabbit manure weekly and from each bin an
average of 3.7 kg (wet weight) of worms were harvested per month
during a six month test period.
The amount of earthwormsrequired
for 10% of the diet could be supplied in under three months with
a
106
growing area of 6.7 m
2
.
Commercial yields from similar sized bins
have been reported at over twice the yields I obtained (Gaddie and
Douglas, 1976).
A major drawback to the incorporation of earthworms into
pelleted fish diets is the labor required to harvest and clean the
worms. It took about two hours to harvest and clean 1 kg wet
weight of earthworms.
If earthworms made up 10% of the pelleted
fish diet it would require 68 hours to harvest enough worms to
produce 45 kg of tilapia at a food conversion of 1.5.
The test diets were pelleted to optimize food conversion
and
to
permit
storage. Swingle
that
production can be twice as great when fish are fed pellets rather
than meal. The Azolla pellet was more stable in water than the
(1958)
demonstrated
water hyacinth pellet. This may be due to the lower fiber content
of the Azolla. Studies indicate that high amounts of fiber reduce
the mechanical strength of pellets (National Research Council,
1977; Robinette, 1977). Earthworm meal appears to be a good
binding agent as it decreased pellet weight loss in both the Azolla
and water hyacinth diets.
The results of these experiments indicate that an Azolla
diet supplemented with earthworm meal can provide an inexpensive
substitute to commercial diets for tilapia, or can reduce feed costs
by supplementing a commercial diet. More work is needed on the
the detailed nutritional requirements of tilapia and the long term
effect plant diets have on tilapia growth and health.
107
CONCLUSIONS
The interest in energy efficient solar greenhouses in the
United States began during the energy crisis of the late 1970's.
Amory Lovins made an important contribution to the energy debate
by identifying it with social change. The key feature of his
contribution was to pose the question of energy policy in terms of
"soft" and "hard" energy paths which involved social variables such
"scale", "decentralization", "equity", and "participation"
(Lovins, 1976; Lovins, 1977; Lovins, 1978). Solar greenhouses
as
owned and run by individuals, families, or communities seemed to be
an elegant way of addressing the societal, energy, and economic
problems set forth by Lovins.
The research conducted for this thesis has shown that
utilization of the water heat storage for closed system aivaculture
and hydroponics can be a productive expansion of solar greenhouse
To date, however, this technology has not progressed much
beyond the research stage. In fact, solar greenhouse use for food
use.
production has not experienced the widespread implementation that
was anticipated.
There are three levels of aquaculture that can be
integrated
into
solar
greenhouse
production:
commercial,
community, and individual or family.
Very few of the approximate 10,000 acres of commercial
greenhouses in the United States have employed solar greenhouse
technology (Albright et al., 1983; White, 1983), and the integration
of aquaculture as a production component has not seen widespread
commercial application.
There are a number of reasons for this:
1. Solar greenhouses can be very expensive, costing
three to four times more than conventional greenhouses;
2.
The opaque insulated walls of solar greenhouse designs
reduce light and can lead to excessive loss of growth, quality and
crop timing;
The use of high levels of insecticides, fungicides and
chemical growth regulators by the commercial greenhouse industry
prohibits aquaculture integration;
3.
4.
Large thermal masses use valuable growing space and
do not allow the commercial grower to implement the rigid
guidelines for rapid greenhouse temperature transitions that are
frequently required; and
5. Solar greenhouse designs do not lend themselves to
easy expansion
which is
frequently required in commercial
greenhouse development.
It does not appear that in the near future solar greenhouse
technology and aquaculture integration will experience large scale
commercial applications in the United States.
Over the past five years approximately 50 community solar
greenhouses, ranging in size from 30 to 500 m2, have been built
across the United States (Klein, 1983). These greenhouses were
started with funds from various government agencies and the
majority were sponsored by Community Action Agencies as part of
their self-help efforts in the fight against poverty (Klein, 1983).
I am not aware of aquaculture practices implemented in any of these
greenhouses.
109
Today many of these community greenhouses have had to
stop operating because of the lack of funds, inadequate
management, and diminishing community participation (Idoine,
1983; Klein, 1983). It is difficult to predict the future of
community greenhouses, but it is doubtful that aquaculture will play
a significant role in their operation.
The level at which solar greenhouse and aquaculture
technology may have the greatest impact is the individual or family
level. There are many publications describing family size solar
greenhouse construction and crop management (see Head, 1984), and
much of the greenhouse aquaculture research to date has been
conducted at this level (see Introduction).
In 1982 I surveyed 103 solar greenhouse owners in western
Oregon and Washington. Most of these greenhouses were family
owned and attached to the south side of the house to assist in
heating.
The energy analysis presented in Chapter II demonstrated
that heat production is a primary energy output from solar
greenhouse/aquaculture systems. Attaching these systems to
homes is an effective way of utilizing the heat resource.
Of those greenhouse owners surveyed six were utilizing
the water heat storage for aquaculture and two had connected their
aquaculture system to hydroponic units.
Two owners were raising
tropical aquarium fish and the remainder were raising Tilapia spp.
for food and emulating designs developed by the Amity Foundation
(Head and Splane, 1979) or the New Alchemy Institute (Zweig,
1980).
A complaint by those who were raising tilapia for food was
110
that some of the fish never reached an edible size and some of the
harvested fish had an off-flavor. This has also been a problem
with fish harvested from the recirculating design described in
Chapter I.
From 1978 through 1982 1 held fish harvests as free public
At the end of each harvest, the participants were
invited to take the fish home and prepare them any way they
wanted. They were also asked to fill out a questionnaire that
inquired about their cooking method, their opinion about size,
workshops.
texture and flavor, whether they would purchase the fish and at
what price, and how frequently they ate fish. The majority of
fishes harvested were tilapia (Tilapia mossambica) and channel
catfish (Ictalurus punctatus). A total of 217 questionnaires were
returned and the most common objections were that the tilapia were
sometimes too small and that the tilapia and channel catfish
sometimes had an off-flavor. Participants described the offflavor fish as having a "muddy", "algae", or "musty" taste.
The problem of small size in tilapia has been discussed in
Chapter
tilapia populations through
hybridization and androgen sex reversal appears to hold the most
promise in alleviating this problem.
I.
Producing
all
male
The cause of off-flavors in fish is generally attributed to
the compound geosmin produced by species of blue-green algae and
actinomycetes (Thaysen, 1936; Gerber and Lechevalier, 1965;
Aschner et al., 1969; Lovell and Sackey, 1973; Safferman et al.,
1967), but other types of environment related off-flavors are also
becoming recognized (Lovell, 1983). These off-flavors may be the
111
result of bacterial decomposition of organic compounds or the
result of intensive feeding (Brown and Boyd, 1982; Lovell, 1983).
Removal of off-flavors in live fish requires holding them
in fresh water without feeding for 7 to 14 days (Lovell and Sackey,
1973; Yurkowski and Tabachek, 1974; Hepher and Pruginin, 1981).
The rate of flavor improvement depends on water temperature, with
a
water temperature requiring a shorter period for
higher
improvement (Lovell, 1979).
The recirculating filter design used in this research
maintained acceptable water quality according to literature
standards but it did not prevent off-flavors from developing in the
fish. I was able to remove the off-flavor in live fish by holding
them in 190 liter tanks with clean aerated water for one week, but
this extra step may discourage many people from culturing fish for
food.
A problem with the filter design used in this study was its
inability to remove organic debris created from fish wastes and
uneaten food. Because of the low density of these particles and
greenhouse space constraints gravity settling is not appropriate.
Periodic use of a rapid sand filter would remove particulates and
should improve both water quality and off-flavor.
The compatibility of hydroponics and closed system
aquaculture holds promise for increasing productivity and crop
diversity.
aquaculture
In addition, combining the equipment needs of intensive
and
hydroponics
into
a
single
reuse
system
substantially decreases initial capital costs and operating
expenses. The hydroponic trough design used in this study was
112
inexpensive, simple to integrate with the recirculating system, and
easy to maintain.
The results of this research indicate that fish culture
water can provide most of the nutrients required for hydroponic
tomato production. Because some nutrients were deficient or
borderline deficient, i.e. potassium and magnesium, the fish culture
water should be periodically supplemented with appropriate
fertilizers to maintain optimum and healthy plant production.
The results of the feeding trials with Tilapia mossambica
show that duckweed supplemented with 10 percent earthworm meal
can be a low cost alternative, or supplement, to commercial diets.
The long-term nutritional impact of the duckweed-earthworm diet
still needs to be evaluated and vitamin and mineral supplements may
be required in intensive culture systems.
An important factor that is often neglected in the study of
family-scale greenhouse aquaculture designs is the time required to
construct and operate such facilities (see Chapters II and III).
Understanding these time requirements will be important to the
successful implementation of greenhouse aquaculture.
113
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