AQUAPONICS: PROTEIN AND VEGETABLES FOR DEVELOPING COUNTRIES.
Michael A Nichols
Institute of Natural Resources, Massey University, Private Bag 11-222,
Palmerston North, New Zealand.
m.nichols@massey.ac.nz
&
Nick A Savidov
Alberta Agriculture, Food and Rural Development,
Brooks, Alberta, T1R1E6, Canada.
Keywords; fish, hydroponics, environmentally friendly, water efficient.
Abstract
Aquaponics is the land based production of fish in tanks combined with the recirculation of
the water from the fish tanks through hydroponic systems to produce high value horticultural
crops. The waste products from the fish are converted by a bio-filter into soluble nutrients
which are absorbed by the plants, and allow “clean” water to be returned back to the fish.
Thus it produces valuable fish protein with a minimal pollution of fresh water resources,
while at the same time producing horticultural (usually vegetable) crops.
The production of fertilizers is becoming increasingly expensive due to high prices of fossil
fuels, and this may have long term implications for nutrient use in agriculture in the future,
particularly in developing countries. Aquaponics uses waste products derived from animals
and plants which are fed to the fish, and thus converted into valuable animal protein and fresh
vegetables.
With the world’s fresh water resources limited, aquaponics would appear to have
considerable potential for developing countries.
Introduction
In many (if not all) developing countries there are major nutritional deficiencies in protein
and in essential minerals and vitamins. The basic carbohydrate diet does little to provide
adequate levels of these essential nutrients.
Aquaponics may provide an effective and efficient means to provide both animal protein
(fish) and mineral and vitamin sources (fresh vegetables) to populations where water/and or
fertilizer resources are limited with a minimum of environmental pollution.
The basic principals of aquaponics is that fish are fed “waste plant and animal material”,
which they convert into protein. The waste material from the fish is then used by plants as
the nutrient source, and the water is then re-circulated back to the fish tank. An essential
component of this is a bio-filter (between the fish and the plants) which essentially comprises
bacteria which converts the waste products from the fish into soluble nutrients for the plants.
An absolutely critical component of this is the conversion of urea (excreted by the fish) into
nitrite, and then nitrate because high levels of urea in the water are toxic to fish. The solid
waste (fish faeces and unconsumed food) is usually filtered off and converted into soluble
nutrients in a separate bypass.
Aquaponics was developed as an extension of aquaculture, and thus the people developing it
have normally had strong aquaculture backgrounds, and (usually) very limited horticulture
backgrounds. This has proved a major limitation to development, because the bulk of the
income is normally derived from the horticulture stream (70%), but the expertise is usually
not in this area. The horticultural product has to compete with conventionally grown
horticultural products on a “level playing field” with the result that in many cases, although
the aquaponics component is effective, the lack of horticultural skills causes the project to
fail. Essentially the fish must be regarded simply as manure producers for the plants, with
the added bonus that there is a small income stream from them also.
Fish farming is popular in many parts of the world—particularly in Asia, but the systems
used tend to pollute the waterways, or are limited to ponds in which a permanent fish/simple
plant ecosystem exists, without any recirculation.
A re-circulating aquaponics system not only is capable of providing a regular supply of fresh
vegetables, but also does so in a non-polluting situation.
It is usual to have a number of fish tanks (usually a minimum of 4), so that fish can be
segregated in terms of size (age) in case of cannibalism, and this also ensures a steady stream
of nutrient to the plants. If all the fish were the same size, then they would all be harvested at
the same time, but by having a range of different ages, then a continuous supply of nutrients
to the plants is assured, because only the fish from a single tank are harvested when they
reach the appropriate size. Similarly it is desirable to have crops of different ages in the
“hydroponic system” to ensure a steady uptake of nutrients.
Fish species.
There is no real limitation on the types of fish which can be used, although they should be
fresh water types, and should not prefer low water temperatures (eg trout), as the temperature
of the water will be too low for good plant growth. In Australia barramundi and Murray
Cod have been used successfully, but internationally the favoured fish is Tillapia. This will
perform satisfactory at pH below 7.0 an important factor for plant growth in hydroponics.
(see later).
Fish require a regular supply of oxygen in the water, and this is controlled by bubblers in the
tanks, which are connected to electric air pumps. A secure supply of electricity is therefore
absolutely essential. In DPR Korea (North Korea) an EU project has developed an
aquaponics system in a country were the electricity supply is very unreliable by integrating
into the system a back up using solar cells which keep a battery continuously charged. Note
the amount of power required to run an air pump is very small.
Of course there are other pumps in the system for example for pumping the “nutrient
solution” through the system, but these can be out of action for some time without the fish
dying from lack of oxygen.
Essentially the role of the fish to to provide the plants with a cheap source of nutrients.
The bio-filter.
Bio-filters come in all shapes and sizes, but it’s essential role is to provide a large surface
area for the ammonia in the solution to come ion contact with the bacteria which are needed
to convert it to first nitrate and then nitrate. Ammonia at high concentrations is toxic to fish,
so this conversion is the essential part of the aquaponic process. In any case plants prefer to
absorb nitrogen as nitrate rather than as ammonia.
The simplest bio-filter is simply a clump of nylon fishing net, on which the bacteria and other
microorganisms establish. This should be cleaned every month or so. Other bio-filters
include containers filled with polystyrene balls, in fact anything with a large surface to
volume ratio.
Water source.
This is a re-circulating hydroponic system, and the less frequently it is necessary to “dump”
the nutrient solution the better. Thus the purer the water source the better, and simplistically
the lower the sodium and chloride content of the fish feed the better. The best water source
is rain water, and this can be collected if necessary using plastic sheets (eg rain shelters) and
stored in small plastic lined dams.
Horticultural aspects
There are many ways of growing horticultural crops hydroponically, but the simplest system
is to use the floating raft system. This involved polystyrene sheets which float in a shallow
canal filled with nutrient solution which flows from the bio-filter to a sump, from where it is
then pumped back to the fish.
This system is relatively cheap, simple, and nearly fool proof. Bubbles are required the
length of the canal to provide the plant roots with oxygen, but if these are not working for an
hour or so, due to air pump problem, this is not a problem, as the plants (unlike the fish) can
survive. In fact it is possible to grow many vegetables crops without aeration if there is a
small gap between the polystyrene raft and the nutrient solution. (Kratky, 2009)
Starting up can be a problem, as the fish are likely to be small, and the plant nutrient supply
limited, particularly if the appropriate bacteria are not in the system, but a small quantity of
solution from an existing aquaponics set up will act as a starter solution.
Many of the fruit vegetables (tomato, pepper, cucumber, melon, etc) appear to require higher
levels of nutrients in hydroponics, than the leafy vegetables. However at the University of
the American Virgin Islands they have successfully produced such crops using aquaponics
and a floating raft system. Certainly the level of nutrients measured in aquaponic solutions
are considerably lower than those required for conventional hydroponics. (Rakocy et al,
2004; Rakocy et al, 2007),
Possibly because the nutrients are organically derived is the reason??
One of the major difficulties with aquaponics is deciding on the appropriate pH for the
solution. Fish tend to prefer a pH in excess of 7.0, while for plants such a pH is likely to
result in major trace element problems, particularly of iron deficiency.
The UVI approach has been to keep the pH at about 7.0 and to use high rates of chelated iron
in the nutrient solution, but at Brooks it has been found preferable to run the system at a ph of
6.7-6.8, at which level the Tillapia appear to thrive, as do the plants. (Savidov et al, 2007)
Pest and disease control
Because fish are a integral part of the system it is impossible to use any pesticides which
might harm the fish. Because of this, it is general to rely only on biological control methods.
It does appear that some of the root disease problems of conventional hydroponic systems
(such as Pythium and Phytophthora) are reduced due to the balance of microorganisms in the
aquaponic solution exerting some form of biological control.
Conventional hydroponics v aquaponics
There have been few studies undertaken which have compared conventional hydroponic
systems with aquaponics. In Italy Pantanella (2011) Table 1 showed that in the first cycle the
conventional system was superior, but in the next cycle there was no significant difference in
yields between conventional hydroponics and aquaponics. In New Zealand (Lennard and
Nichols, 2011) Tables 2 & 3 have demonstrated that aquaponics production can exceed
conventional hydroponic production in the right situation. They found lower productivity
form the aquaponic system in the winter when the fish were relatively inactive due to low
water temperatures, and the feeding rate was reduced, resulting a a lower production of plant
nutrients, but higher yields from the aquaponic system during the warmer summer months.
Conclusions
Aquaponics would appear to offer developing countries where animal protein and fresh
vegetable supplies are limited with the opportunity to produce both in a single simple
production system which pronominally uses waste animal and plant material to produce fish
protein and vegetables rich in minerals, vitamins and fibre. The value of the fish might be
further enhanced because of the potential of containing such importance micro-nutrients as
ω3.
References
Kratky, B A (2009) “Three non re-circulating hydroponic methods of growing lettuce” Acta
Hort., 843, 65-71.
Nichols M A & Lennard W (2010)_Aquaponics in New Zealand. Practical hydroponics and
Greenhouses. , 115, 46-51.
Pantanella, E, Cardarelli, M, Colla, G, Rea, E & Marcucci, A (2010) Aquaponics vs
hydroponics: Production and quality of lettuce crop. 28th IHC Abstracts I, 35.
Rakocy, D S, Schulz, J E, Bailey, R C & Thoman, E S (2004) “Aquaponic production of
tilapia and basil: comparing a batch and staggered cropping system”. Acta Hort., 742, 63-69.
Rakocy, J E, Bailey, D S, Schulz, R C & Danahar, J J (2007) “Preliminary evaluation of
organic waste from two aquaculture systems as a source of inorganic nutrients for
hydroponics”. Acta Hort., 648, 201-207.
Savidov, N A, Hutchings, E & Rakocy, J E (2007) “Fish and plant production in a
recirculating aquaponic system: A new approach to sustainable agriculture in Canada” Acta
Hort., 742, 209-221.
.
Table 1 Comparison betweeen aquaponics and hydroponics
Lettuce yield (kg/m2)
1st experiment
Aquaponics LD
2.37 b
Aquaponics HD
2.71 a
Hydroponics
2.84 a
Significance
*
LD = Low Fish Density (5kg/m3)
HD = High Fish Density (8kg/m3)
2nd experiment
Aquaponics LD
Aquaponics HD
Hydroponics
Significance
LD = Low Fish Density (6kg/m3)
HD = High Fish Density (20kg/m3)
5.67
5.7
6.02
ns
Table 2: Aquaponic and hydroponic NFT lettuce variety comparisons – Summer (February)
2010
Variety
Top Weight (g)
Hydroponic
Top Weight (g)
Aquaponic
Sig Diff?
Better System
Difference (%)
Gaugin
Princess
Explore
Ashbrook
Satre
Robinio
Obregon
130.83
117.00
211.86
220.25
173.11
177.88
142.50
168.00
246.63
293.78
266.38
223.56
204.43
223.40
Yes
Yes
Yes
Yes
Yes
No
Yes
Aquaponic
Aquaponic
Aquaponic
Aquaponic
Aquaponic
Neither
Aquaponic
28
111
39
21
29
57
Table 3: Aquaponic and hydroponic NFT lettuce variety comparisons – Winter (August)
2010
Variety
Top Weight (g)
Hydroponic
Top Weight (g)
Aquaponic
Sig Diff?
Better System
Difference (%)
Gaugin
Princess
Explore
Ashbrook
Satre
Robinio
Obregon
271.61
177.38
709.47
497.67
322.20
293.22
354.87
327.44
204.94
625.93
453.17
349.20
345.78
341.53
Yes
No
No
No
No
Yes
No
Aquaponic
Neither
Neither
Neither
Neither
Aquaponic
Neither
21
18