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32
Technical Report Series
32
Number 73-7
I
A MANUAL OF FLATFISH REARING
J
by
David B. White
and
Robert R. Stickney
31
31
Georgia Marine Science Center
University System of Georgia
Skidaway Island, Georgia
81
A MANUAL OF FLATFISH REARING
by
David B. White
and
Robert R. Stickney
Skidaway Institute of Oceanography
P. 0. Box 13687
Savannah, Georgia 31406
September 1973
The Technical Feport Serits of the Georgia Mari.ne Scie nce Center is
issued by the Georgia Sea Grant Program and the Marine Extension Service of
the University of Georgia on Skidaway Island (P. 0. Box 13687, Savannah,
Georgia 31406). It was established to provide dissemination of technical information and progress reports resulting from marine studies and investigations
mainly by staff and faculty of the University System of Georgia. In addition, it
is intended for the presentation of techniques and methods, reduced data and
general information of interest to industry, local, regional, and state governments and the public. Information contained in these reports is in the public
domain. If this prepublication copy is cited, it should be cited as an unpublished
manuscript.
Table of Contents
I.
Table of Contents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
11
II.
List of Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
111
II I. List of Figures . • . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . • • • 1v
IV. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1
V.
Culture Facilities at Skidawav Institute of Oceanography . . • . . . . . . . • . • 2
VI.
Basic Culture Techniques
. . . . . . . . . . . . . . . . . . . . . . . . . . .
Supplies of Eggs for Culture.
4
. . . • • • • • . • . • . • • . . . • • • • • • 5
Larval Food and Disease Control
8
Collection and Care of Postlarvae and Juveniles
12
Nutrition of Postlarvae and Juveniles
. . . . . . . . . . . .
13
Environmental Conditions for Paralichthys Culture • . . . . . . • . • • • 18
VI I. Conclusions and Recommendations
19
Choosing the Site for Culture . . . . . . . . . . . • . . . . • . . . . • . . . . . 19
Building the Physical Plant . • . . . . . . . . . . . . . . . . • • . • • . . • • • 21
VI II. Bibliography . . . . . . . . . . . . . . • . . . . . . . . . . . . . . . . . . . . . . . . . . 25
IX.
Tables .
X.
Figures
. . . . . . . . . . . . . . . . . . ... . . . . . . . . • . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . .
ii
28
31
List of Tables
Table 1
Selected Environmental Parameters of some Laboratory Reared
Flatfish . . .
0
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
28
Table 2
Essential Amino Acid Requirements of Plaice and Sole . . • • . • . . 29
Table 3
Composition of Artificial Pelleted Diets of Cowey et al (1970)
and Stickney and White. . . . . . . • • . • • . • • . . • . • • • . 30
iii
List of Figures
Figure 1. Flatfish under culture at the Skidaway Institute of Oceanography:
Paralichthys dentatus (bottom) and Ancylopsetta
quadrocellata • . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
Figure 2. Fiberglass swimming pool filters used for secondary
filtration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
Figure 3. View of water table with aquarium sized fiberglas s tanks in
which postlarval fish are maintained. . . . . . . . . • . . . . • . . . . . • . . • 33
Figure 4. Schematic of 1 meter diameter fiberglass tanks for rearing of
juvenile flormder . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
Figure 5. The lower side of a Paralichthys dentatus demonstrating both
ambicoloration and extensive papillomas associated with an
outbreak of the virus Lymphocystis. • . . . . . . . . . . . . . . • • . . • • • • • 35
Figure 6. Growth of Paralichthys dentatus during 1972 and 1973 demonstrating
increased growth caused by physical plant improvements between
those years. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
lv
INTRODUCTION
Severe worldwide protein deficiencies that are evident today and promise
to increase with the Earth's population have made man aware of one of his
last appare nt exploitable sources of food -- the sea. However, with our
current knowledge of the world ocean as an ecosystem it has become increasingly
clear that man is presently exploiting this system at close to its maximum
sustainable yield (Ryther, 1969). This fact, coupled with the enormous expense
and legal problems that arise when a country maintains a national fishing fleet
which fishes the coastal waters of other nations has caused many countries to look
into the potential for management of sections of the oceans in an attempt to
increase the yield per unit area and thus to minimiz e the cost of harvesting
food from the sea.
Culturing of aquatic
animals~
se dates back at least two thousand
years; however, most of the knowledge gained by early culturists was not
recorded and hence is lost to present generations.
The late nineteenth century
saw an awakening of interest in the rearing of aquatic organisms in North America.
At that time effort was mainly directa:i toward the augmentation of comme rcial
fisheries by the release of large numbers of hatchery reared larval and postlarval
forms into the oceans.
Tremendous amounts of capital and energy were thrown into
work in this area and consequently a considerable amount of knowledge was collected
on spawning and rearing techniques, although attempts at supplementation of natural populations were eventually abandoned when they proved ineffective . The
flatfish (Pleur onectiformes) as a group were well represented in this early research
1
and information on this group began to appear in scattered publications as early as
the 1880's. In the 1920's financial hardships and unfavorable returns from their
efforts caused the closing of many hatcheries.
Within this period of time,
however, flatfish became established as suitable animals for laboratory studies
due to their ease of maintenance.
For this r eason scattered information has been
compiled until the present.
The object of this report is to gather the pertinent flatfish literature,
to condense the most relevant information and to present generalized procedures
and recommendations for the production of marketable flatfish from eggs.
The
techniques presented in this paper were taken from the literature and from work
conducted at the Skidaway Institute of Oceanography on three species of flatfish
(Paralichthys dentatus, P. lethostigma and Ancylopsetta quadrocellata) (Figure 1).
Cons ide ring that information on numerous species is presented in this
paper, it is obvious that a detailed account cannot be given on each; however,
further information is available in the bibliography.
This paper is meant to be an
introductory presentation to the layman who desires to work with one or more
phases of the life cycle of the flatfish, and should serve as an introduction to the
literature and culture techniques for interested scientists. An anno tated bibliography
bas been prepared by us to provide additional reference material (White and Stickney,
1973).
CULTURE FACILITIES AT SKIDAWAY INSTITUTE OF OCEANOGRAPHY
A flow through water system is utilized in our culture system. Water is
taken from the Skidaway River, passed through a gravel filter, secondarily
2
filtered through sand swimming pool pressure filters (Figure 2), and UV sterilized water is then heated to desired temperature by a fuel oil heater equipped
with a stainless steel heat exchange r.
Prior to the 1973 experiments the secondary
filter and UV systems had not been installed and bacterial disease problems we r e
encountered.
modified.
These problems have largely been avoided since the system was
A detailed description of the water system and culture building is
presented in a technical report by White,
~ al.
(1973).
Postlarval flounder are reared after capture in 50 l fiberglass culture
tanks which are placed in water tables for temperature control (Figure 3).
The
water is static within these tanks where the fish remain until they reach between
0 . 1 to 1. 0 g.
The water tables can be accurately maintained at a desired
temperature by adjusting a series of valves which mix ambient and heated salt
water and allow it to flow around the culture tanks.
The large reservoir of
heated water within the water tables also serves to reduce heat loss from the
culture tanks during power failures or shutdowns of the water supply system for
maintenanc e or repair.
One meter diameter fiberglass tanks, each supplied
with running water and equipped with a Venturi drain system are used for fish
once they outgrow the aquarium sized tanks (Figure 4 ).
During the design phase a recirculating system was considered as a
possibility but abandoned in favor of the flow-through system prese ntly in use .
Several reasons were involved in that dec is ion.
1) A recirculating system requires a biological filter to remove waste
products from the water, and while such filters have been designed and used in
freshwater systems with varying degrees of sue cess, the technology of biological
3
filters in conjunction with marine systems is generally lacking. After some
experience with biofilters we realized that inordinate amounts of time and
effort could be spent in developing and maintaining these filters.
2) A biological filter was deemed impractical since running several experiments
simultaneously would require an individual filter for each experiment and treatment.
For systems where the mixing of effluents would not create problems a
closed or semi-closed system might be more practical.
3) Experiments testing various environmental parameters such as
salinity and temperature would be difficult in a closed system because of mixing
of treatment waters in reservoirs and filters.
could be run at a time.
In practice only one treatment
This is neither temporally or scientifically desirable.
4) Because of the clay turbidity, included organic matter and bacteria associated with raw Skidaway River water ,an elaborate filter system would be required
even in a closed system since makeup water must be available on demand.
BASIC CULTURE TECHNIQUES
The pleuronectiform fishes generally have small pelagic (floating) eggs which
follow normal symmetrical tEieostdevelopment through the early larval stages
(Norman, 1934). Pearcy (1962) discussed other flatfish with demersal (sinking)
eggs. At a late stage of development, metamorphosis, the characteristic
flatfish features (lateral compression of the body and migration of one of the eyes
from one side of the body to the other) are manifested.
After metamorphosis, the
flatfish acquire their benthic habit which will persist for the rest of their lives.
As would be expected, the stress put on the animals in changing from planktonic
or pelagic to benthic habits and from the physical changes in body configuration are
4
gr eat.
Young flatfish are heavily preyed upon by larger fishes, inc luding adult
flatfish; thus , in nature only a small fraction of the larval flatfish survive me tamorphosis . This is made up for by the fact that females often lay over one hundred
thousand eggs per spawning season, depending on species.
SUPPLIES OF FLATFISH EGGS FOR CULTURE
There are three means by which fertilized flatfish eggs may be obtained
by cultur ists:
1.
Collection by plankton nets
Flatfish generally spawn in the winter months.
Depending upon spec ies,
the spawning ground may be in inshore estuaries or in deep offshore waters.
Shortly after fertilization, the pelagic eggs may be easily obtained by surface
plankton net tows over the spawning area with nets of 1 mm mesh size or sma lle r.
The eggs are first sorted from eggs and larvae of other species, then placed in
appropr iate sized containers and supplied with gentle ae ration until they can be
returned to the laboratory.
Unfortunately, there is little a va i.l able information on
identification of the eggs of flatfish and one usually ends up with an assortment
of species .
2. Natural spawning in confinement
A second and more sophisticated means of obtaining fertilized eggs is
to trawl for sexually mature or maturing adults on the spawning ground and return them to spawning tanks on the shore. Sexing of flatfish is usually accomplished by holding the animal up to a strong light source and observing the
internal anatomy.
In many species the sex can readily be determined by the
presence or lack of distended ovaries which extend posteriorly in the abdom inal
5
cavity .
Of course, as the flatfish approach sexual maturity the distinction becom es
more obvious even to the extent that most running ripe females exhibit such s wollen
ovaries that the outline of those organs may be easily distinguished externally
on the fish.
In any case, several animals of both sexes are usually placed in the
same tank to insure fertilization.
Shelbourne (1968) has had considerable success with plaice (Pleuronectes
platessa) using tanks 3.7 x 3.7 x 1.2 meters deep and placing 30 to 40 adults
(30 to 40 em in length) in each tank.
These tanks are kept in an area of low
illumination and have a slow flow of sea water. Plaice readily spawn in these tanks
with no artificial inducement. Of course, when using a flowing sea water system,
screens must be placed over all exit ports to prevent the loss of the pelagic eggs .
This means of obtaining flatfish eggs eliminates the tedious step of sorting vast
amounts of mixed plankton which often results in fatal damage to eggs.
Conversations with W. W. Anderson of the Georgia Game and Fish
Commission reveal that gravid summer and southern flounder (Paralichthys
denta 1lls and
!? .
lethostigma, respectively) are not taken in trawls made by the
Commission in the estuarine and nearshore waters of the state. It is possible that
Paralichthys do not spawn in Georgia waters, or that their spawning ground is
located in deeper water, as found for_!?. denta1lls off New England (Smith and
Fahay, 1970). During the winter of 1972-73 two_!?. lethostigma females which
were maintained in a 2 m diameter fiberglass outdoor tank at Skidaway Institute of
Oceanography were found to have developing ovaries. No males were available
at the time, thus no attempt at spawning could be made. One of these fish
6
subsequently died during a severe cold spell, while the other resorbed her eggs
when the water began to warm in the spring.
The fact that some development
occurred is encouraging, and it is felt that spawning under controlled conditions can
be carried out once sufficient brood stock are collected. It was initially felt
that deep water might be required for spawning; however, the development of_E.
lethostigma in the 1 m deep tanks indicated that laboratory spawning might be
feasible.
3. Artificial spawning
in confinement
A third approach to obtaining flatfish eggs is by artificial spawning.
This
technique has been followed for years by fisheries biologists working with various
species of fish.
Basically the technique is as follows: The ripe female is grasped
with one hand over the head region, the other hand about midpo int on the animal.
Slight pressure is applied to the sides of the fish (i.e. top and bottom of flatfish)
by both hands while at the same time moving the hands toward each other. Eggs will
flow freely from a running ripe female.
The eggs are usually extruded into a bucket
with about 1 em of sea water at the same temperature from which the adult fish
were taken.
Milt from the male is deposited in the same manner over the eggs
and the mixture is gently stirred and allowed to sit for 3-5 minutes.
Excess milt
is then washed from the eggs by filling the bucket with fresh sea water. Fertilized
pelagic eggs will float to the surface within a few hours and can be skimmed off
by dip netting.
The remaining water, milt and unfertilized eggs are then discarded
and the fertilized eggs are washed with several changes of the proper temperature
7
sea water (see Orcutt, 1959; Hildebrand, 1930; Smith and Fahay, 1970; Mito, et al.,
1960; Gutherz, 1970 ; Houdi,
embryological development).
~ al.
, 1970; Miller and Marak, 1962, for details on
This method is the primary method used in selective
breeding.
Difficulty may arise when fish eggs are crowded, the consequences of which
often cannot be distinguished until after hatching. Our work and work conducted
by Shelbourne in Great Britain has indicated that a hierarchial structure is set up
in flatfish populations early in their lives.
Hence, the early hatchlings become the
dominant fish in the tanks and may prevent smaller fish from obtaining sufficient
food. Juvenile oscellated flounder, Ancylopsetta qu3()rocellata, and both Paralichthys
dentatus and
~·
lethostigrna with which we have worked showed this pattern when post-
larval individuals of different sizes were stocked toge the r at low stocking densitie s.
The pattern often disappeared at high densities. Shelbourne (1968) suggested a
stocking density of 1, 000 to 2, 000 eggs per tank (60 x 30 x 30 em filled to a depth
of 20 em), but the optimum stocking number probably varies considerably and should
be determined for each species.
LARVAL FOOD AND DISEASE CONTROL
To obtain the largest percentage survival of flatfish eggs and larvae environmental conditions must be optimized. Ideal temperature and s alinity requirements
for development vary according to species.
The effects of parameters such as
photoperiod, light intensity, stocking density and othe r s may also vary. Optimum
environmental parameters will have to be discovered by additional work on each
species since , in general, such work has not been carried out (see Table 1).
There are, however, two major concerns common to all larval fish development
8
that should be considered: food (including food presentation) and disease control.
Ea rly flatfish culturists used phytoplankton as larval food, apparently
believing that larval pleuronectiform fishes were herbivores. In all cases m ortality
rates were near 100 percent. Rollefsen (1939) discovered that several marine
larval fish are carnivorous and readily accept the easily cultured brine shrimp,
Artemia salina.
Since that time nearly all flatfish rearing techniques have in-
cluded the use of brine shrimp as a food for larvae and postlarvae. Several
other types of food, including chopped oysters, fish, shrimp and naturally
occurring zooplankton have been used as food with some success. Since most
of these foods are dead when served, two major drawbacks are present: 1) the
fish must be trained to accept non-living food since they are sight feeders and
normally accept only living food (de Groot , 1971), and 2) the dead and decaying
food may promote bacterial and ammonia build-up in the tanks unless a running
sea water system is utilized. Non-living foods may be excellent for juveniles after
the flatfish have developed sufficient hunting prowess, but for larvae and postlarvae
A. salina is probably the best readily available food item.
The readily available brine shrimp A. salina is collected from two main
sources: The Great Salt Lake, Utah; and San Francisco Bay, California. Nauplii,
hatched from canned eggs, are the main food source for larval marine fishes in
the lab, although freeze-dried adult A. salina are also available. Hatching is
accomplished by vigorously aerating sea water to which the brine shrimp eggs
have been added.
The greatest percentage hatch occurs at 25 C and 25-30 ~
salinity. Hatching takes place in 24-48 hours depending upon environmental
9
conditions.
To facilitate feeding and minimize bacterial buildup problems in fish culture
tanks, the hatched nauplii are usually separated from the unhatched eggs and egg
fragments.
This is easily done by taking advantage
taxic response.
of~.
salina's positive photo-
In our culture system a light is placed over the open end of a
half covered opaque container and the nauplii and egg mixture is added to the covered
side.
The nauplii readily swim to the lighted end and are concentrated below the
light. An even more thorough separation is obtained by placing a solid partition
between the lighted and dark ends of the tank. When a narrow slit is left parallel
to the bottom of the tank near the bottom, the brine shrimp quickly swim through
the slit to the lighted side of the tank. Most of the unhatched eggs and egg fragments remain on the dark side.
To make brine shrimp more visible to larval Paralichthys we have found
that an opaque rearing tank with bright overhead lights is advantageous. Shelbourne
(1968) recommends a black lining inside the rearing tanks and a light intens ity
of 500 m. c. (meter candles) at the water surface (as measured with a light meter
sensitive to the vertebrate eye) for the culture of plaice.
Light intensity can be
reduced gradually as the eyes of the fish become better developed and as the
animals become efficient hunters [see Blaxter (1968) for a discussion on light and
vision in plaice].
Normal bacterial counts of about 1, 000/ml are average in the sea (Zobel!,
1946) but may increase several thousand-fold when eggs have been added to sea
water under hatchery conditions. Attempts to control marine bacteria with ultraviolet light have met with some success. Oppenheimer (1955) found that several
10
combinations of drugs controlled marine bacteria in the presence of marine
fish eggs and that a combination of penicillin with streptomycin in concentrations
of 50 parts per million (ppm) of each drug in the water was effective in reducing
bacterial populations. yet not detrimental to the larval fish.
Shelbourne (1963)
found that a single dose of 50 IU of sodium penicillin G per ml and . 05 mg streptomycin sulphate per ml of sea water in a static system was effective in controlling
bacteria in the presence of plaice eggs. Shelbourne placed fertilized eggs in the
static system until the eggs hatched and removed newly hatched larvae daily to
another tank of running water to begin their development through the larval stages.
Not only did treatment produce a larger percentage hatch of plaice eggs , but those
larvae which hatched in the treated tanks were significantly stronger than those in
untreated tanks.
Due to contamination of the Skidaway River by coliform and other bacteria,
disease problems plagued our research during 1972. The placement of secondary
filters and UV sterilization in the water system prevented a recurrence during
1973. Among the diseases we experienced during 1972 was an outbreak of
Lymphocystis virus
(FigureS~
While the fish were not killed directly by this
disease, their feeding was impaired by growths around the mouth, even1ually
leading to starvation , and growths on the fins cleared the way for bacterial infections.
The danger of introducing disease by obtaining fish from the wild is great,
another good reason why controlled spawning should be attempted.
Prophylactic treatments of formalin (about 25 ppm) biweekly have been used
to retard or prevent disease outbreaks. We do not recommend such treatment unless
11
indicated by poor water quality (in terms of bacteria) or suspected disease. Several
U.S. government publications are available which help the culturist identify and
control disease problems and usually can be obtained from County Extension
Agents of the U. S. Department of Agriculture.
COLLECTION AND CARE OF POSTLARVAE JUVENILES
Since gravid Paralichthys sp. have not been obtained from Georgia coastal
waters, it has been necessary to collect flounders for culture studies as postlarvae
and juveniles. Initial attempts at collection of suitable stock by otter trawling
during 1971 resulted in a low number of animals varying significantly in size at
capture. During January and February, 1972, about 2000 postlarval Paralichthys sp.
were collected from the vicinity of Beaufort, North Carolina in 1 meter diameter
1 mm mesh plankton nets . During the same months in 1973 postlarvae were
collected both from North Carolina and from the Skidaway Rive r in Georgia.
Nets are set from stationary objects on incoming tides after dark and checked for
contents every 1/2 hour. Towing of nets usually results in poor success since the
animals are large enough to a void the boat wake and are, thereby, missed by the
net. Smaller mesh or diameter nets have also proved to be impractical because
the increased size of the hydrostatic cone which exists in front of these nets also
causes avoidance.
Upon return to the laboratory the postlarval flounders are placed under
static water conditions in fiberglass 50 1 capacity tanks at the temperature and
salinity of capture, or the temperature and salinity in which they were brought to
the lab.
They are maintained under those environmental conditions for about one
12
week after which the tempera1llre is gradually raised to 25 C (from about 5- 10 C
at cap1llre) in two degree increments per day for several days.
maintained during this period at about 25
The fish are fed brine shrimp
~
The salinity is
°/oo .
salina) nauplii ad libi1llm twice daily
beginning immediately after their arrival at the laboratory.
We have experienced
no difficulty in establishing the postlarvae on Artemia.
The fish are stocked in the fiberglass tanks at a density which allows them
all to settle on the bottom of the tanks with a total coverage of no more than
50 percent of the substrate area. Aeration is provided by a blower and air stones .
Ammonia tends to concentrate in the static system and the water must be changed
at least twice weekly . The ammonia level should never be allowed to exceed 0. 5 ppm ,
although the fish can survive levels over 1 ppm for short periods.
NUTRITION OF POSTLARVAE AND JUVENILES
With the use
flatfish.
of~
salina as food it is possible to produce metamorphosed
The small amount of a·vailable literature on cultivation of flatfish past
this stage of development is recent because, as already noted, earlier culturists
were interested only in producing larval flatfish to supplement natural populations.
Juvenile flatfish have been reared on several types of natural food: chopped fish or
shrimp, oysters and even living shrimp; however, these items are often difficult
to obtain or maintain and may vary widely in nutritional content.
Artificial diets,
on the other hand, can be easily stored and have precise nutritional content.
Aquaculture and many types of research on flatfish must rely on suitable artificial
diets.
Unfor1llnately, little nutritional work on marine or estuarine species has
13
been undertaken.
Thus, initial dietary investigations must be carried out using
basic nutritional principles as well as nutritional information obtained from work
conducted on freshwater or anadromous fish .
Early in our research a means was found by which flounders caul d be
converted from natural living foods to artificial diets. We found that only a small
percentage of flounder would directly consume artificial fry food (pellets) after
they had been feeding
on~.
salina.
The majority of the postlarvae would, however
feed on frozen chopped penaeid shrimp.
After a two week period floating, laboratory
prepared freeze-dried shrimp was substituted for the frozen shrimp.
then began feeding from the s urface.
The fish
When floating commercially available pellets
were fed a few weeks later the majority of the flounder converted to the artificial
diet.
This procedure was relatively simple since several thousand anima ls at the
postlarval stage can be held in a small area. A single freeze dried shrimp was
sufficient to feed several hundred animals for one day.
Floating pellets proved to
be superior to sinking pellets since uneaten portions could easily be removed from
the tank with dip nets.
This prevented fouling of the water which often occurs with
sinking pellets. Also, since the fish feed by sight and are attracted by motion,
the floating pellets may have stimulated feeding behavior for a longer period than
did sinking pellets which, once they reached the bottom, seemed more difficult
for the fish to locate.
Aquaculture presents several unique problems which are not found in
terrestrial culture systems - one of these is the method of presentation of food.
In terrestrial animal husbandry a major problem is presentation of the ration with
14
an odor or taste that leads the animal to consume the feed.
In aqua tic systems one
has this problem also, but more importantly one must present the ration in a form
that does not disperse rapidly in water (a condition which results in benefit only
to microorganisms).
Most often the ration is prese nted as a pellet, varying in s ize
depending upon age and species being cultured.
Feeds used for small scale laboratory
studies usually are high protein rations containing a binder such as gelatin, agar
or finely divided collagen. Water may be added to form paste which is extruded
through a large syringe and either dried or frozen for storage.
Larger scale
operations require a pellet mill or mechanical extruder which have the adva ntage
that both the length and diameter of the pellets may be easily controlled.
In
addition, much larger amounts of ration can be prepa r ed at one t ime, insuring
homogeneity of the diet throughout an experiment.
Freezing of a ration after it
has been dried prevents microbial decomposition of the pellets and subsequent
poisoning of the fish as a result of peroxidation of lipids in the ration. Normally
no more than two or three weeks ration is left at room tempera ture.
Rather extensive dietary research has been carried out on the freshwater
salmonid fishes (trout and salmon) and on the channel catfish, Ictalurus punctatus.
Of the five general classes of nutrients: vitamins, lipids, carbohydrates , minerals
and proteins, detailed work with flatfish nutrition has been conducted only on proteins.
However, a preliminary study by us showed that sucrose and glucose produced
better growth than does corn starch in the oscellated flounder (A ncylopsetta
quadrocellata).
rainbow trout.
Kitamikado, et al. (1964) have published similar data on the
Their work demonstrated that the digestibility of certain proteins
15
decreased as the starch content of the diet increased . J . W. Andrews (pers onal
communication), on the other hand, has shown that channel catfish,
are able to utilize starch at high levels.
!:
punctatus,
He feeds corn starch at up to 40% in
purified diets. It might be speculated that trout and at least some flatfish that
are normally carnivorous have not developed the e nzyme system necessary for
utilization of large amounts of starch whereas catfish and other fish which ingest
considerable amounts of carbohydrates, due to their omnivorous or herbivorous
feeding behavior, have developed a system to obtain benefit from this class of
food.
Cowey et al. (1970a) succeeded in defining the essential amino acid
requirements of the plaice (Pleuronectes platessa) and sole (Solea solea) and found
them to be qualitatively similar to those of the Pacific salmon (Table 2).
up study, Cowey et
~·
In a follow-
(1970b) determined that increased protein levels up to 70 %
(as casein) produced increased growth.
They did not determine if levels higher
than this would p r oduce more rapid growth rates. Work conducted by us at
Skidaway Institute of Oceanography with.!: quadrocellata showed similar results.
Semi-purified diets with up to 70 % fish meal (43. 5% protein) produced better growth
as the percentage of fish meal increased. In addition to pelleted diets, groups of
A. quadrocellata were fed chopped frozen fish and shrimp ad libitum. Results over
the same period showed a growth rate on these "natural foods" of nearly twice
that of the highest protein pelleted diet.
Whether this is attributable to a high
protein level found in these foods or to some other factor is not yet clear.
Summer flounder, Paralichthys dentatus, when fed in our laboratory a
16
commercially available fish feed of 40% protein have shown growth rates exceeding
those in nature for this species as reported by Smith (1969), Hildebrand and Schroeder
(1928) and Smith and Fahay (1970).
Figure 6 illustrates the growth of thirty X: dentatus
from one gr am to over 120 grams during 1972. Several power failures and water
system malfunctions during this time caused widely varying temperatures a nd other
less than optimum conditions to exist for a large portion of the time .
Figure 6
represents an encouraging growth curve for this species. Recent changes in the
water system (White et
l!J. ,
1973) have reduced some of the earlier problems a nd
allow the maintenance of a more suitable environment in the cultur e tanks.
Growth
of a group of 30 rapidly growing P. lethostigma captured during January , 1973, is also
presented in Figure 6 and shows the results of modification in the water system.
Table 3 presents the composition of diets producing the best growth rates
for Cowey et al. (19 70b), and our work with A. quadrocellata. Cowey fed a moist
pellet extruded from a large veterinarian syringe.
The dry components of the diet
we re mixed 1:1 with water to which a taste attractant (assorted amino acids) had
been added.
The diet was stored under refrigeration until used. In our studies
dry pellets were fed at a rate of 5% of the total biomass within each tank daily .
Pellets had been extruded wet from a small laboratory extruder (Model X-5,
Wenger Manufacturing Company, Sabetha, Kansas, U.S. A. ) and dried overnight at
50 C.
Fish meal and fish oil present in the diet appeared sufficiently attractive
to induce rapid consumption.
It should be noted that corn starch -is the primary
carbohydrate in this diet. As stated earlier, substitution of glucose or sucrose
would be expected to produce better growth.
17
It should also be noted that other
va ria tions between the two diets are also found in the vitamin, mineral and fat
conte nt, yet both produced positive growth.
ENVIRONMENTAL CONDITIONS FOR PARALICHTHYS CULTURE
Deubler (1960), Deubler and White (1962) and Peters and Angelovic (1971)
have demonstrated that postlarval_£. lethostigma
and~·
dentatus grow most rapidly
°
at salinities as high as 30 /oo. Stickney and White (1973) have demonstrated
s imilar results for postlarval Paralichthys lethostigma.
Their data further
indicate that salinity requirements change rapidly with age and that within a few
months after capture juvenile southern flounder grow most rapidly at salinities
as low as 5 to 10
°/oo .
This change in optimum salinity requirement with age
probably relates to the normal migrational pattern of Paralichthys .
Fish of this
genus hatch in highly saline offshore waters and then move to low salinity estuarine
waters to grow.
They eventually move back offshore during the winter months
where they breed as 2 or 3 year old adults.
Peters and Angelovic (1971) demonstrated that 30 C produces the most
rapid growth in postlarval summer flounder.
However, the exact temperature
requirements of summer and southern flounder juveniles have not yet been
defined, although maintenance in the range of 20-30 C has provided excellent
growth and feed consumption in our studies.
We have found that late larval and early postlarval
R·
dentatus and
R·
lethostigma
reared in our laboratory feed well with a surface light intensity of 300 to 500 foot
candles (1 foot candle
= 10.76
meter candles).
This intensity is obtained by
placing a four foot double bulb fluorescent light fixture approximately three feet
above the water's surface.
18
CONCLUSIONS AND RECOMMENDATIONS
Choosing the Site for Culture
Studies conducted with Paralichthys dentatus and P . lethostigma at
Skidaway Institute of Oceanography have acquainted us with many of the problems
involved with flatfish culture and we have been able to overcome a few of them.
The feasibility of rearing Paralichthys sp. on a commercial scale has not been
ruled oot, but a good deal more information will be required before a profitable
venture can be undertaken .
The selection of a proper site is probably the most important step toward
establishing a facility for the culture of P . dentatus orE· lethostigma . Ideally,
the location should include:
1.
Low levels of dissolved or suspended solids. Water of low turbidity is highly
desirable in culture facilities because outbreaks of disease organisms are
often as sociated with particulate material in the water.
The lack of particulates
is also desirable in that extensive maintenance cleaning of the culture facilities
is eliminated and for aesthetic reasons.
Feeding is also enhanced in cl ear
water since the fish are better able to see food particles.
must be kept low in culture facilities.
·~
Turbidity
The culturist has the choice of
costly filtering or finding naturally low turbidity water prior to initiation of
culture.
2.
Low bacterial and viral levels. Bacterial disease outbreaks are costly and
often difficult to control while viral infestations are nearly impossible to
control.
The stresses placed on animals under aquaculture conditions create
se vere problems. In general, good water quality and proper nutrition provide
19
a degree of protection against disease.
All fish carry disease organisms
and outbreaks are likely following any period of stress .
3.
The site should be located away from any type of industrial or municipal
pollution.
4.
The water supply should be 5 to 20
°/oo salinity .
Higher salinity water could
be diluted to the appropriate salinity but increasing salinity through use of
additives is not recommended for reasons of economics.
Flounder are
able to live through most natural oscillations in salinity but may go off food
during these periods.
5.
Water with a constant tempera1llre of approximately 25 C (77 F) should provide
r apid growth. Although no tempera1llre requirement experiments have been
carried out with juvenile flounder
w
~.
results in our lab
have shown
that temperatures of 30 C (86 F) retard growth and mortality increases
rapidly at temperatures above this level. Both
E.
denta1lls and g. lethostigma
are able to withstand temperatures of less than 10 C (50 F); however, growth
is reduced at temperatures below 20 C (68 F). Optimum tempe ra1llres
(between 20 and 30 C) may not be available throughout the year at any
location; however, the site should be chosen in an area where extended
periods with water temperature within this range occur. Water may be obtained
by pumping surface waters or from salt water wells (if such wells are
feasible in the area selected).
Certain types of salt water wells may provide
constant temperature throughout the year, but in most cases some variability
should be expected .
20
6.
The site should be located near readily available stocks of brood fish, eggs or
postlarvae.
One of the greatest problems encountered in work with Paralichthys
sp. in Georgia was the una vailability of large numbers of postlarvae and
juveniles for stocking. Plankton ne tting for laboratory animals is feasible,
but the number required for an aquaculture venture would be prohibitive
in many cases unless an area was found in which extremely high densities
of these fish were found.
Maintenance of brood stock, or collection of ripe
adults from the field and subsequent artificial spawning provide the only real
hope for successful aquaculture of these species.
The development of strains
of rapidly growing, hearty animals will ultimately depend upon artificial
spawning of selected brood animals and will require a number of years to
develop. At present the natural variability in growth rate of flounder captured
from nature is a problem. Our work has indicated that tempera ture is the
most important aspect of initiation of gonad development in adult animals .
We strongly recommend that future aquaculturists learn to maintain and
propagate brood fish now that the feasibility of rearing the offspring has
been demonstrated.
Building the Physical Plant
Certain characteristics are required in the construction and operation of a
proper physical plant for the cul1ure of flounder.
In our attempts to evolve a
working physical plant we have found that the least costly facility requires a high
initial capital outlay.
Many of our recommendations are described in detail in a
previous tec hnic al report (White
1.
~al.,
1973).
Cons truction of a well insulated laboratory.
21
During embryonic and larval
development flounder must be reared indoors under precise control of
environmental conditions.
Temperature control can only be considered if
a well insulated laboratory is provided. A block building over a cement
floor with good ceiling insulation provides adequate temperature control if
the proper water heating and or cooling equipment is installed. With proper
site selection, temperature modification can be avoided resulting in a great
economic saving. A network of permanent floor drains to carry water from
the building eliminates extensive plumbing.
Epoxy paint over the walls
and ceilings facilitates cleaning and is well worth the extra expense.
Plumbing
should all be of PVC (polyvinyl chloride) including all pipes, valves and
fittings.
Metal valves (even brass) last for only a few months in the
corrosive atmosphere of salt water. If metal is required anywhere it should
be of high quality stainless steel.
2.
Construction of outdoor culture facilities.
Our research has been confined to
laboratory scale studies, and it is obvious that a viable aquaculture operation
would require much more physical space.
Tank culture does not appear to
offer a realistic possibility for a commercial venture at this time, and most
aquaculture operations would presumably be confined to ponds or enclosed
lagoons, bays, cages, etc . We have not had an opportunity to work with
such outdoor facilities, but some of the limitations to be expected with
such installations are readily apparent. Water quality deterioration associated
with increased oxygen demand as a result of high density stocking, supplemental feeding and potential noxious algae blooms is a primary consideration.
If the system is open to a natural saltwater area of any type the presence of
22
predators and fouling organisms within the ponds or other enclosures can
be expected. In addition, fish and other organisms which enter the ponds
from the outside will consume food meant for the flounder. As we have
already mentioned, the constant threat of disease outbreak is always
present and would be enhanced in cages, lagoons and ponds receiving
tidal flushing.
These realities are associated with any outdoor marine system,
and many of them apply to freshwater also. Since salt water wells are not
always a real alternative, some filtration of pond water may be required
to remove unwanted organisms.
3. Substrate requirements. Virtually all of the fish which we have reared beyond
a size of 5. 0 em have shown greater or lesser degrees of ambicoloration.
By the time the fish reach a year of age the extent of ambicoloration is often
great (Figure 5 ). This could have an effect on marketability of fish which
are normally sold with head and skin intact. The development of pigment
on the underside of flounder may be preventable if the fish are provided with
a substrate in which they can bury (Stickney and White, submitted for publication). Such a substrate should be made available soon after the fish are
captured and must consist of extremely fine material in which the small
flounder are able to bury.
Fine sand effectively reduces the amount of light
reaching the lower surface of the flounder buried in it and thus prevents
the development of dark pigment on the blind side of the fish .
In conclusion, it appears feasible to rear some species of flatfish under
controlled or semi-controlled laboratory conditions; however, basic knowledge on
23
specific environmental and nutritional parameters is not now available for most
flatfish species. Some of this information is beginning to appear in the literature
as interest in flatfish aquaculture increases and as scientists are discovering the
importance of these fish in the oceanic food web. When experience has led to the
development of adequate skills by aquaculturists good survival rates should be
achieved through the critical larval stages and be yond to market size. Once the
postlarval stage is reached it appears that the flatfish are characterized as being
extremely hearty and easily adaptable to laboratory conditions.
ACKNOWLEDGMENTS
The authors with to thank Messrs. Daniel Perlmutter and Rodney Zeigler
for assistance in obtaining and maintaining the flatfish used in research carried
out at Skidaway Institute of Oceanography. We also wish to thank Ms. Barbara
McNair and Nancy Fair for typing the manuscript.
This work was supported by the Sea Grant Office of the National Oceanic
and Atmospheric Administration under Grant Number 1-36009.
Tbis paper
is meant to serve as a final report to Sea Grant as regards the flounder
project of Sea Grant Number 1-36009, as well as serving as an outlet for
information derived from that project.
24
Bibliography
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flounder. Pseudopleuronectes americanus (Walbaum) in Rhode Island.
Trans. Am. Fish. Soc. 94:259-264.
Blaxter, J. H. S. 1968. Light intensity, vision and feeding in young plaice .
J. Exp. Mar. Biol. Ecol. 2:293-307.
Breder, C.M . , Jr. 1923. Some embryonic and larval stages of the winter
flounder . U.S. Bur. Fish. Bull. 38:311-316.
Brice, J. J. 1898. A manual of fish-culture, based on the methods of the United
States Commission of Fish and Fisheries. Reports of U.S. Comm. Fish.
1897.
Cowey, C.B., J.W. Adron, A. Blair. 1970a. Studies on the nutrition of marine
flatfish: The essential amino acid requirements of plaice and sole.
J. Mar. Bioi. Assoc. U.K. 50:8 7-95.
Cowey, C .B., J. W. Adron, A. Blair and F. Pope. 1970b. The growth of
0-group plaice on artificial diets containing different levels of protein.
Helgolander Wess. Meer. 20:602-609.
de Groot, S. J . 1971. On the interrelationships between morphology of the alimentary
tract, food and feeding behavior in flatfishes (Pisces: Pleuronectiformes).
Neth. J. Sea Res. 5:121-196.
Deubler, E.E. 1958. A comparative study of the postlarvae of three flounder
(Paralichthys) in North Carolina. Copeia. 1158:112-116.
Deubler, E.E. 1960. Salinity as a factor in the control of growth and survival
of postlarvae of the southern flounder, Paralichthys lethostigma. Bull.
Mar. Sci. Gulf and Carib. 10:338-345.
Deubler, E.E. and J.C. White. 1962. Influence of salinity on growth of postlarvae
of the summer flounder, Paralichthys dentatus. Copeia, 1962:468-469.
Gutherz, E.J. 1970. Characteristics of some larval bothid flatfish and development
and distribution of larval spotfin, Cyclopsetta fimbriata (Bothidae).
Fish. Bull. 68 (2):261-283.
Hildebrand, S.F. and W.C. Schroeder. 1928. Fishes of the Chesapeake Bay. Bull.
U.S. Bureau Fisheries. 43:366pp.
25
Hildebrand, S. F. and L. E. Cable. 1930. Development and life history of
fourteen teleostean fishes at Beaufort, N. C . Bull. U. S. Bureau of
Fish. 46:383-488.
Houde, E.D., C.R . Futch and R. Detwyler. 1970. Development of the lined
sole, A rchirus lineatus, described from laboratory-reared and Tampa
Bay specimens. Fla. Dept. Nat'l. Res. Research Ser. No. 62:43pp.
Howell, B. R. 1972. Preliminary experiments on the rearing of larval lemon
sole Microstomus kitt (Walbaum) on cultured foods. Aquaculture 1:38-44 .
Kitamikado , M. , T. Morishita and S. Tachino. 1964. Digestability of dietary
protein in rainbow trout II. Effect of starch and oil contents in diets
and size of fish. Bull. Jap. Soc. Scient. Fish. 30:50-54.
Miller, David and R.R. Marak. 1962. Early larval stages of the fourspot
flounder, Paralichthys oblongus. Copeia . 1962 (2) :454-455.
Mito, S . , M. Ukawa and M. Higucch. 1969 . On the egg development and rearing
of the larvae of a flounder, Kareius bicoloratus (Baselewsky) with
reference to its spawning in the culturing pond. Bull. Nanei Reg. Fish.
Res. Lab. 1:87-102.
Norman, J.R . 1934. A systematic monography of the flatfishes (Heterosomata).
Vol. 1: British Museum N.H.: 459 pp.
Oppenheime r, C. H. 1955. The effect of marine bacteria on the development
and hatching of pelagic fish eggs and the control of such bacteria by
antibiotics. Copeia. 1:43-49.
Orcutt, H. G. 1950. The life history of the starry flounder, Platichthys stellatus
(Pallas). Calif. Dept . Fish. Game Fish Bull. 78:64pp.
Pearcy, W.G. 1962. Distribution and origin of demersal eggs within the order
Pleuronectiformes. J. Cons. Perm. Inter. Explor. Mer. 27(3):232-235 .
Peters, D. S. and J. W. Angelovic. 1971. The effect of temperature, salinity
and food availability on growth and energy utilization of juvenile summer
flounder, Paralichthys dentatus. ·Proc. Third National Symposium on
Radioecology, in press.
Poole, J. C . 1966. Growth and age of winter flounder in four bays of Long Island
(Pseudopleuronectes americanus). N.Y. Fish and Game. J. 13:206-220.
Rae, B.B. 1965. The Lemon Sole. The Whitefrtars Press Ltd. London. 106pp .
26
Rollefsen, G. 1939. Artificial rearing of fry of sea water fish. Preliminary
communication. Rapp. Cons. Explor. Mer. 109(3):133-134.
Rythe r, J. H. 1969. Photosynthesis and fish production in the sea. Science.
166:72-76.
Scott, W.C.M. 1929. A note on the effect of temperature and salinity on the
hatching of eggs of the winter flounder (Pseudopleuronectes americanus,
Walbaum). Contrib. Can. Biol. 4:137-141.
Shelbourne, J . E. 1953. The feeding habits of plaice postlarvae in the Southern
Bight. J. Mar. Bioi. Ass . U.K. 32:149-161.
Shelbourne, J . E. 1963. A marine fish-rearing experiment using antibiotics.
Nature (London) 198:74-75.
Shelbourne, J. E. 1968. In "Marine Aquaculture" Edited by W. J. McNeil,
Oregon State University Press. Corvallis, Oregon:15-36.
Smith, R . W. 1969 . Analysis of the summer flounder (Paralichthys dentatus L.)
population in the Delaware Bay. U. of Delaware M.S. Thesis. 71pp.
Smith, W.G. and W.P. Fahay. 1970. Description of eggs and larvae of the
summer flounder Paralichthys dentatus. U.S. Fish and Wildlife Ser.
Res. Rep. 75:21 pp.
Stickney, R.R. and D.B. White. 1973. Effects of salinity on the growth of
Paralichthys lethostigma postlarvae reared under aquaculture conditions
Proc. 27th Ann. Conf. S.E. Assoc. Game and Fish Comm.: in press.
White, D.B. and R.R. Stickney. 1973. Annotated bibliography of flatfish
(Pleuronectiformes) research, Ga. Marine Science Center Technical
Report Series: in press.
White, D.B., R.R. Stickney, D. Miller and Lee H. Knight. 1973. Sea water
system for aquaculture of estuarine organisms at the Skidaway Institute
of Oceanognp hy. Ga . Mar. Science Center Technical Report Series:
in press.
Zobell, C. E. 1964. Marine Microbiology. Chronica Botanica Co. Waltham.
Mass.: 240 pp.
27
TABI.l·. I
SJ:.Lf:CT£0 EN1.1110NMENTAL PAilAMf:TEils OF SOME L,\ BOHATOH\ Jli.AilLil FU
1.(;(;
tim e
tlmt· rr()m
ll.mp.
! ' ish
l
S;t liOJI \
P. P. r.
Jt \.EN 111.1ll:\ 1'101' \I J.N;
LAlli AL OJ:. I ELOP MENT
LUlP~tf.:-11
IH. I
rt·rt. lo
h:ttl'hln~
Temp.
Sa tlnlty
P.P.T.
rF1~11
lo
ytk. abs.
hatch
:~ fl.
(rln,l's)
food [cd
upon ylk.
nbsorp.
umc to
metamorphosls
sin· ul
S;ilinll\
Temp.
P. P.1.
tlnw to
Sl':\ .
nLit.
,ldUh
·~ml
,C),
or
1'1.!~"' nf
idlJi l
uptlll\Uin
p.i\\'OinJ,!;
pC'ak
spa wru n~
~l'
ll'nl l ~
IS flll
-,ji. IWI IIIll!
dqll h(lllt
Art.cmla
1\)
0>
\l hirU"\
lint· LW:o;
-,-1,-
.!i =2
:1 1""'2
nauplu
and smal l
zooo lonk .
J "'da •s
10-11
davs
.1:1n-Jul'
2-3
months
h.iu
f t - :1)
a r.t IC' 1
Sh:lilow
\;ti'H.'li
;\IH' I'Oslnmus
11-1:1
:141
Hda ·s
I••
:J:!
li hours
fi- 10°
30
J0-1 5°
25-35
35 - 10
6- 10°
30
:! years
em
100,000
700,00(1
fi.S
loc:t lh
1\t:t r- .\u •
loll -1 1111
!'\0\ - Jk.·l'
:.!-, - 111
\ 'S
growth
flt.·nt;I W S
f1-7l
:10 - 40
100 .000
300 000
40 em
11, 000000
b~s t
Artemia
naup li i
40
a1
Artemia
nau plil
Pl:ltit: h th\s
.. td l:iw ~
,,.., hours
).! ..-.
l'l
12 . 5°
.. - 5
and
otht:rs
35
4- 5
Artemla
Dat.r.plii
0-35
tn nature
2-3 years
10-1:}
0
l>t.:t·-.Ltn
l ~kUI'Orl l 'l"lt:~
pi.tlt.'S~:t
I~ I - Ill 1
11-l
:r-,
~1
davs
7-~0
100- 150
49davs
11-1 2°
35
5 vea.rs
oou
1•~ •.:udup ll'U-
soo, uou
~
tnH'nt•;tnu~
1.) - }M
lll-151
11• -JIIIlltk',
.:,,
, ,,
I~~
:1-;J
t.'t
:11.
:~:?
•. ,
oq~"· '
-!lti\\P}J t 1 ·t':2t
- H :II,' t 1 ~~~;.-,I
- Dl'u hl t· r 11!1.-, ... ,
',;,
lh ldt•hr;mcl a nd Lahll' 1 J!l:lllt
d;J\"!;
2- :l
32.3
12- H
ffil- PC'Iers und A!le bvlc (1971)
(il- Smith nnd Fahav ( 1970)
( 8)- Orrutt (1950)
(9)- Shclbourne (1 953)
(I 0)- She! bourne (1968)
60dil\"S
32
32- 3
(11) - Ber n , et ol. (1 9(ifi)
Bredor (19n l
(12)
Dri ce (11{9M)
(1 3)
(14)- Poole (1966)
(15) - Scott (1929)
-
3- 4) cars
1 billion
1-1
h ·h-.\ l.tl
-,
..
TABLE 2
ESSENTIAL AMINO ACID REQUIREMENTS OF
PLAICE AND SOLE1
Amino Acid
Regutrements in
Plaice
Requirements in
Sole
Alanine
Arginine
+
+
Histidine
+
+
Isoleucine
+
+
Leucine
+
+
Lysine
+
+
Methionine
+
+
Pheny !alanine
+
+
Threonine
+
+
Tryptophan
N
N
Tyrosine
*
*
Valine
+
+
Asp artie Acid
Cysteine
Glutamic Acid
Glycine
Proline
Serine
1.
+
-
*
N
Mter Cowey, Adron and Blair (1970) .
Indicates a dietary source required
Indicates a dietary source not required from ordinarily available material.
Probably from hydroxylation of Phenylaline.
Not determined.
29
TABLE 3
COMPOSITION OF ARTIFICIAL PELLETED DIETS OF
Cowey et al., (1970) * and Stickney and White
COWEY et al. *
% of dry diet
Skidawa;y Ins t. Studies
% of dry diet
Protein
70 (as casein)
43.5 (70% of diet
as fishmeal)
Dextrin
7.3
Vitamins
4. 5
1.0
Minerals
4.0
2.5
Corn oil
4.0
Cod liver oil
3.0
COMPONENT
1.0
Fish oil
Alpha cellulose
2.0
10.0
Corn starch
Binder
4 . 0 (as guar gum)
Food attractants
* Cowey,
10.5
.2
Adron, Blair and Pope (1970)
30
5. 0 (as agar)
Figure 1. Flatfish under culture at the Skidaway Institute of Oceanography:
Paralichthys dentatus (bottom) and Ancylopsetta quadrocellata.
31
Figure 2. Fiberglass swimming pool filters used for secondary filtration.
Figure 3. View of water table with aquarium sized fiberglass tanks in which
postlarval fish are maintained.
..-A
B
On e meter cu ltur e tank. A. 6 inch .outer ~tand pipe. B. ll inch
i nn e r s tand pipe. C. Floor of tank with slope t awa rd th e te~te r.
D. ltinchthreadedP.V.C . flangewithleginserted. E . l r tnch
e lb ow wi th flexible hose connection for drain .
Figure 4. Schematic of 1 meter diameter fiberglass tanks for rearing of
juvenile flounder.
34
j
Figure 5 . The lower side of a Paralichthys dentatus demonstrating both
ambicoloration and extensive papillomas associated with an
outbreak of the virus Lymphocystis.
I
140
120
100
80
~
0
u.,
0)
...,:
~
60
40
20
4
8
12
16
20
24
1972 •
•
1973 A
A
28
32
WEEKS
Figure 6. Growth of Paralichthys dentatus during 1972 and 1973 demonstrating increased
growth caused by physical plant inprovements between those years.