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Two low-maintenance culture systems for small pelagic marine animals
Aquaculture, 65 (1987) 375-383 Elsevier Science Publishers B.V.. Amsterdam
375 -
Printed
in The Netherlands
Technical Paper
Two Low-Maintenance Culture Systems for Small Pelagic Marine Animals CL. BROWNELL’
and D.A. HORSTMAN’
‘Marine Biology Research Institute, Department of Zoology, University of Cape Town, Rondebosch 7700 (South Africa) *Biological Oceanography Section, Sea Fisheries Research Institute, Private Bag X2, Rogge Bay 8012 (South Africa) (Accepted
18 March
1987)
ABSTRACT Brownell, C.L. and Ho&man, D.A., 1987. Two low-maintenance marine animals. Aquaculture, 65: 375-383.
culture systems for small pelagic
Two simple tank designs are described and a list of the approximately 65 species of planktonic marine and estuarine organisms, mainly fish larvae and copepods, that have been reared or cultured in them is given. The first tank is a single-pass, flow-through version of the well-known false-bottom, or sub-sand filter system. The material used to cover the nylon-mesh bottom is either carbon sand or polyurethane foam. The second tank, called a “hoist-transfer tank”, has a smooth bottom sloping to a central drain. It is also operated on a single-pass, flow-through basis, the cultured organisms being retained by means of a submerged cartridge filter. It is capable of being physically raised or lowered by a winch. Before microfauna on the walls or bottom of a culture tank begins to significantly inhibit reproduction and growth of the organisms being cultured, the tank volume is transferred to a similar clean tank. Transfer is done by connecting a tube between the drains of the dirty and clean tanks and lifting the former relative to the latter. Both tank types receive a twice-daily, automatically dispensed suspension of phytoplankton food.
INTRODUCTION
There are dozens of methods and devices available for maintaining or culturing relatively small numbers of pelagic marine copepods, fish larvae, or other small plankters of similar requirements (reviewed by Kinne, 1976,1977). The essential considerations in the design of such systems are typically the following. (1) Maintaining adequate water quality requires exchange of water, either on an intermittent or continuous basis. (2) Maintaining an adequate food supply requires periodic addition of a suspension of phytoplankton or other food. When many cultures are being maintained simultaneously, an automatic food-dispensing system saves labor and reduces the possibility of accidental introduction of undesirable organisms.
0044-8486/87/$03.50
0 1987 Elsevier Science Publishers
B.V.
376
(3 ) Except in the case of very rapidly reproducing organisms, maintaining a desired density requires some method of retaining them in the culture volume while excess water is allowed to escape. (4) Maintaining a hygienic environment in the culture vessel requires periodic cleaning of the tank walls and bottom, or periodic transfer of all or part of the culture into a clean vessel. The systems described below developed out of an attempt to approach the above considerations with an emphasis on reliability and low maintenance.
THE CULTURE SYSTEMS
The following descriptions of the culture apparatus corresponding to the four criteria listed above.
are arranged in four parts
1. Input water
Incoming sea water is treated in the same way for use in both false-bottom and hoist-transfer tanks. It is drawn subtidally, settled, sand-filtered in two stages, membrane-cartridge filtered (1 pm), and pumped to a temperaturecontrolled, aerated header tank before passing into the culture vessels. Water enters the tanks via opaque polyethylene tubing on a continuous basis at a rate of about 0.3 ml min-’ 1-l of tank volume. 2. Food supply Up to six phytoplankton species (Skeletonema costatum, Chaetoceros gracilis, Tetraselmis suecica, Pseudoisochrysis paradoxa, Pavlova lutheri, and Hymenomonas sp. ) are cultured in 300-l polyethylene bags in a temperaturecontrolled room with fluorescent lighting. Twice daily, phytoplankton is pumped simultaneously from the bags and automatically distributed to the culture vessels at a rate of about 20 ml (10~40, depending on species and density) of phytoplankton suspension per litre of tank volume per day. The phytoplankton distribution system is to be described in more detail elsewhere. Briefly, a microcomputer operates all the essential pumps, solenoid valves, and the dispensing apparatus according to programmed instructions. A predetermined amount of the mixed phytoplankton is apportioned to each culture vessel and the lines are automatically rinsed with hot fresh water before the next cycle.
377 overflow
rtondpipe
“...._,
holes
a+...”
“‘-..~-.
opaque
inspection
cover,
flap.,., ‘..
\water in
desired W*+H level
overflow
foam ..charcoal
hose
or sand
rupport~
\perforated fiberglass
corrugated roofing
drain
Fig. 1. Two versions of the false-bottom culture tank. Arrows indicate direction of water flow. (A) 150-l fiberglass tank with internal overflow. The tank is drained by pulling out the overflow standpipe. (B) 500-l asbestos-cement tank with external overflow. The tank is drained by dropping the external hose to the ground.
3. Retention of cultured organisms (a) False-bottom tanks Fig. 1. These culture tanks are versions of the vessels used to rear marine fish larvae (Brownell, 1979). A nylon mesh of 60-300 pm pore size is firmly attached to the tank walls with a non-toxic adhesive. Either a l-3-cm layer of carbon sand (0.5-1.5 mm diameter) or a &cm sheet of polyurethane foam overlies the nylon mesh. The sand and foam are porous enough to allow detritus to be drawn into the interstitial spaces where it is less likely to come in contact with the animals being cultured. They greatly prolong the length of time the underlying mesh can be left in the tank without fouling. Culture tanks presently employing this retention system range in volume from 25 to 450 1.
mriridgc filter
......
lid
-
JL
Fig. 2. Hoist-transfer tanks. (A) The 150-l tank on the left is being drained into an identical clean tank on the right via the connecting hose. The suspended tanks of the upper tier are not shown. (B) Side view of rear of tank showing arrangement of overflow system employing a 30-50-pm filter cartridge.
319
(b) Hoist-transfer tanks (Fig. 2 ) , In these tanks detritus is allowed to settle onto the otherwise clean, bare tank bottom. Overflow water is screened by a replaceable, washable, pleated cartridge filter of nominal 30-50 pm pore size. 4. Tank cleaning (a) False-bottom tank. The advantage of a retention system employing a false bottom with sand or foam is that the tank can be kept in operation for extended periods without cleaning. This may range from 3 weeks (relatively sensitive pelagic marine rotifer Synchaeta hutchingsi) to 6 months (robust estuarine copepod Pseudodiuptomus hessei) . Thorough cleaning of the tank is moderately time consuming because it requires the removal of the culture and washing of the sand or foam. (b) Hoist-transfer tanks. The vertically moveable tank was conceived to facilitate culture transfer and tank cleaning. The tanks are designed to be raised or lowered by means of a winch (Fig. 2A). By connecting a tube between the bottom drain of a dirty tank containing the culture and the drain of a clean tank, and raising the former relative to the latter, the culture is easily and completely transferred to the clean tank. The air and water lines leading to and from the tanks are flexible and long enough so that they can be left intact when the tanks are raised or lowered by cables clipped onto stainless steel tabs. The tabs are welded to stainless steel plates bonded into the fiberglass tank walls. The transfer hoses are equipped with self-sealing garden snap fittings and no tap is required at the bottom of the tanks. After use, the transfer hoses are rinsed with hot water and hung to dry. Air and water valves are attached to a board mounted on the wall behind the tanks. Each incoming water line is equipped with a medical intra-venous drip chamber mounted on the same board. The water flow to each tank can be checked at a glance and adjusted if necessary without opening tank lids. Air is released at the lowest point in the tank as a slow stream of large bubbles. The overflow filter cartridge is arranged as shown in Fig. 2B. Because of limited space in the temperature-controlled room in which this system is operating, the tanks are square, rather than round, and are arranged in two tiers. Each tier is comprised of 11 tanks. The lower tier consists of 1501 tanks which rest on the floor, the upper tier consists of 60-l tanks that are suspended from an overhead girder. Only the lower tier is shown in Fig. 2A. Any of the lower tanks can be raised and any of the upper tanks can be lowered when a culture is to be transferred. One tank in each tier is kept empty at all times and cultures are routinely transferred between tanks according to a predetermined schedule, typically on a 2-6-week cycle.
380 TABLE 1 List of species that have been cultured in the false-bottom tanks. All fish species listed were reared from the egg through metamorphosis. All non-piscean zooplankton listed were cultured through multiple generations TELEOSTEI Clupeidae Etrumeus whiteheadi Sardinops ocellatus Engraulidae Engraulis capensis Scomberesocidae Scomberesox saurus Gadidae Gaidropsarus capensis Soleidae Heteromycteris capensis Synaptura kleini Cynoglossidae Cynoglossus capensis Carangidae Trachurus trachurus Centracanthidae Pterosmaris axillaris Syngnathidae Hippocampus capensis
Sparidae Chrysoblephus laticeps Diplodus sargus Diplodus cervinus Gymnocrotaphus curvidens Lithognathus mormyrus Pachymetopon blochi Argyrozona argyrozona Pterogymnus laniarius Mugilidae Mugil cephalus Scorpaenidae Coccotropsis gymnoderma Congiopodidae Congiopodus spinifer Triglidae Trigla capensis Atherinidae Atherina breviceps Amphiprionidae Amphiprion percula
COPEPODA Calanidae Calanus finmarchicus australis Calanus carinatus Canthocalanus minor Paracalanidae Paracalanus scotti Temoridae Temora discaudata Centropagidae Centropages brachiatus Pseudodiaptomidae Pseudodiaptomus hessei P. serricaudatus Acartiidae Paracartia africana Acartia natalensis Pseudocyclopidae Pseudocyclops xiphiphorus
Cyclopidae Halicyclops dedeckeri Oithonidae Oithona nana Oithona similis Cyclopinidae Cyclopina sp. Cletodidae Cletocamptus trichotus Tisbidae Tisbe holothuriae Longipediidae Longipedia weberi Tachidiidae Euterpina acutifrons Harpacticidae Tigriopus aff. californicus
381
TABLE I (continued) BRANCHIOPODA Sididae Pen&a avirostris Artemiidae Artemia salina
AMPHIPODA Ceinidae Austrochiltonia subtenuis Eusiridae Paramoera capensis
OSTRACODA Cypridopsidae Sarscypridopsis S. sp. B
CILIATA Strobilidiidae Strombidinopsis sp. Codonellidae Tintinnopsis beroidea Tintinnidae Eutintinnus tubulosus Metacylididae Metacylis jorgenseni Helicostomella subulata Undellidae Proplectella pentagona Climacostomatidae Fabrea salina Condylostomatidae Condylostoma sp. Strombidiidae Strombidium sp. Ptychocylididae Favella campanula F. serrata
sp.A
ROTIFERA Brachionidae Brachionus plicatilis Euchlanidae Colurella colurus C. dicentra Synchaetidae Synchaeta hutchingsi S. vorax
RESULTS
Twenty-five species of marine fish have been reared to date from the egg through metamorphosis in the false-bottom tanks ( Table 1) . Many more were reared well beyond the first-feeding stage. Forty-two species of crustaceans, rotifers, and ciliates have been taken through multiple generations in the falsebottom tanks. At the time of this writing the hoist-transfer tanks have been in operation for 4 months and only seven species have been tested during that time. All were successfully cultured through multiple generations with low maintenance: Calunus finmarchicus australis, Paracalanus scotti, Centropages brachiatus, Pseudodiaptomus hessei, Paracartia africana, Acartia natalensis, and Brachionus plicatilis. DISCUSSION
Nearly all rearing and culture systems described in the literature involve significant continuous or periodic water renewal. Some experimentalists, how-
382
ever, have successfully reared or cultured marine zooplankton, including fish larvae, in relatively small volumes with little or no water exchange over extensive periods. Lasker et al. (1970) kept early larvae of northern anchovy (Engruulis mordax) for 5 weeks in static, 10-l containers. Hettler (1981) reared Atlantic menhaden (Brevoortia tyrannus) for the first month under static conditions. Klein Breteler (1980) cultured several marine copepod species over periods of at least 3 weeks in static containers. There are many other examples. The practice of rearing marine zooplankton in the presence of healthy and actively growing phytoplankton (Struhsaker et al., 1973) may pertain here. In the above examples, Hettler (1981) conducted his rearing in the presence of Chlorellu, Lasker et al. (1970) in the presence of the autotrophic dinoflagellate Gymnodinium splendens, and Klein Breteler (1980) in the presence of the heterotrophic dinoflagellate Oxyrrhis marina. It is possible that ChZoreZZu, Gymnodinium splendens, Oxyrrhis marina, and certain other species of autotrophic and heterotrophic microplankton can create beneficial conditions in a static rearing tank that might otherwise only be approached via water exchange or frequent tank cleaning. The development of microbial slimes on the surfaces of objects exposed to sea water is a widely recognized phenomenon ( ZoBell, 1972; Fletcher and Marshall, 1982). The factors that control the species composition and ecological succession of these slimes (through predator-prey interactions, competition for space and nutrients, ectocrine release, etc. ) are poorly understood. Nevertheless, it has become apparent to the present authors that microbial slimes can have deleterious effects on cultured animals, and that one way to reduce their effects is to physically remove the slimes or to transfer cultures to clean tanks at frequent intervals. Another way to reduce their effects seems to be to maintain healthy populations of certain species of microplankton in the tank. Part of the beneficial effect of the microplankton may be to biologically control populations of deleterious free- or substrate-living organisms. The volume of culture that can be accommodated in the false-bottom and hoist-transfer tanks is limited for practical reasons. In the former, a very large tank requires a correspondingly large amount of bottom sand, which must be cleaned each time the tank is renewed. In the latter, a restriction is placed on the size of tank that can be conveniently raised or lowered. Nevertheless, for specific purposes, intermediate-size tanks may be ideal. For fish larvae the false-bottom tanks are appropriate when relatively small numbers ( ~5000) of eggs are available. The entire larval stage may be passed without cleaning the tank or even removing dead larvae. For pelagic copepods, rotifers, and ciliates, the hoist tanks are particularly suited for long-term maintenance of stock cultures. The animals may be periodically transferred to much larger tanks for batch-culture mass production, as is done at the Sea Fisheries Research Institute laboratory. High copepod densities were achieved using the equipment described above.
383
In hoist-transfer and false-bottom tanks with continuous water flow, cleaned every 2 and 3 weeks, respectively, the copepods Puracartia africana, Parucalanus scotti, and Pseudodiaptomus hessei attained densities over 1000/l, of which at least 20% were adults. P. scotti attained a density of 1750/l in a 150-l falsebottom tank. In static systems using Oxyrrhis marina (Klein Breteler, 1980)) copepod densities were much lower (20-40/l). The ideal, medium-size culture system for marine zooplankton is no doubt still in the future. When it is finally developed, it will very possibly employ continuous water exchange as well as one or more biological measures to control deleterious microbial ectocrines.
REFERENCES Brownell, C.L., 1979. Stages in the early development of 40 marine fish species with pelagic eggs from the Cape of Good Hope. Ichthyol. Bull. J.L.B. Smith Inst. Ichthyol., 40: 84 pp. Fletcher, M. and Marshall, K.C., 1982. Are solid surfaces of ecological significance to aquatic bacteria? In: K.C. Marshall (Editor), Advances in Microbial Ecology, vol. 6. Plenum Press, New York, NY, pp. 199-236. Hettler, W.F., 1981. Spawning and rearing Atlantic menhaden. Prog. Fish-Cult., 43 (2): 80-84. Kinne, O., 1976. Cultivation of marine organisms: water-quality management and technology. In: 0. Kinne (Editor), Marine Ecology, Cultivation, Vol. 3 (1). Wiley, London, Chapter 2, pp. 19-300. Kinne, O., 1977. Cultivation of animals. 5.1. Research cultivation. In: 0. Kinne (Editor), Marine Ecology, Cultivation, Vol. 3( 2). Wiley, London, Chapter 5, pp. 579-1229. Klein Breteler, W.C.M., 1980. Continuous breeding of marine pelagic copepods in the presence of heterotrophic dinoflagellates. Mar. Ecol. Prog. Ser., 2: 229-233. Lasker, R., Feder, H.M., Theilacker, G.H. and May, R.C., 1970. Feeding, growth and survival of Engraulis mordax larvae reared in the laboratory. Mar. Biol., 5: 345-353. Struhsaker, J.W., Hashimoto, S.M., Girard, S.M., Prior, F.T. and Cooney, T.D., 1973. Effect of antibiotics on survival of carangid fish larvae (Cananz mate) reared in the laboratory. Aquaculture, 2: 53-88. ZoBell, C.E., 1972. Substratum: bacteria, fungi and blue-green algae. In: 0. Kinne (Editor), Marine Ecology, Environmental Factors, Vol. l(3). Wiley, London, pp. 1251-1270.
375 -
Printed
in The Netherlands
Technical Paper
Two Low-Maintenance Culture Systems for Small Pelagic Marine Animals CL. BROWNELL’
and D.A. HORSTMAN’
‘Marine Biology Research Institute, Department of Zoology, University of Cape Town, Rondebosch 7700 (South Africa) *Biological Oceanography Section, Sea Fisheries Research Institute, Private Bag X2, Rogge Bay 8012 (South Africa) (Accepted
18 March
1987)
ABSTRACT Brownell, C.L. and Ho&man, D.A., 1987. Two low-maintenance marine animals. Aquaculture, 65: 375-383.
culture systems for small pelagic
Two simple tank designs are described and a list of the approximately 65 species of planktonic marine and estuarine organisms, mainly fish larvae and copepods, that have been reared or cultured in them is given. The first tank is a single-pass, flow-through version of the well-known false-bottom, or sub-sand filter system. The material used to cover the nylon-mesh bottom is either carbon sand or polyurethane foam. The second tank, called a “hoist-transfer tank”, has a smooth bottom sloping to a central drain. It is also operated on a single-pass, flow-through basis, the cultured organisms being retained by means of a submerged cartridge filter. It is capable of being physically raised or lowered by a winch. Before microfauna on the walls or bottom of a culture tank begins to significantly inhibit reproduction and growth of the organisms being cultured, the tank volume is transferred to a similar clean tank. Transfer is done by connecting a tube between the drains of the dirty and clean tanks and lifting the former relative to the latter. Both tank types receive a twice-daily, automatically dispensed suspension of phytoplankton food.
INTRODUCTION
There are dozens of methods and devices available for maintaining or culturing relatively small numbers of pelagic marine copepods, fish larvae, or other small plankters of similar requirements (reviewed by Kinne, 1976,1977). The essential considerations in the design of such systems are typically the following. (1) Maintaining adequate water quality requires exchange of water, either on an intermittent or continuous basis. (2) Maintaining an adequate food supply requires periodic addition of a suspension of phytoplankton or other food. When many cultures are being maintained simultaneously, an automatic food-dispensing system saves labor and reduces the possibility of accidental introduction of undesirable organisms.
0044-8486/87/$03.50
0 1987 Elsevier Science Publishers
B.V.
376
(3 ) Except in the case of very rapidly reproducing organisms, maintaining a desired density requires some method of retaining them in the culture volume while excess water is allowed to escape. (4) Maintaining a hygienic environment in the culture vessel requires periodic cleaning of the tank walls and bottom, or periodic transfer of all or part of the culture into a clean vessel. The systems described below developed out of an attempt to approach the above considerations with an emphasis on reliability and low maintenance.
THE CULTURE SYSTEMS
The following descriptions of the culture apparatus corresponding to the four criteria listed above.
are arranged in four parts
1. Input water
Incoming sea water is treated in the same way for use in both false-bottom and hoist-transfer tanks. It is drawn subtidally, settled, sand-filtered in two stages, membrane-cartridge filtered (1 pm), and pumped to a temperaturecontrolled, aerated header tank before passing into the culture vessels. Water enters the tanks via opaque polyethylene tubing on a continuous basis at a rate of about 0.3 ml min-’ 1-l of tank volume. 2. Food supply Up to six phytoplankton species (Skeletonema costatum, Chaetoceros gracilis, Tetraselmis suecica, Pseudoisochrysis paradoxa, Pavlova lutheri, and Hymenomonas sp. ) are cultured in 300-l polyethylene bags in a temperaturecontrolled room with fluorescent lighting. Twice daily, phytoplankton is pumped simultaneously from the bags and automatically distributed to the culture vessels at a rate of about 20 ml (10~40, depending on species and density) of phytoplankton suspension per litre of tank volume per day. The phytoplankton distribution system is to be described in more detail elsewhere. Briefly, a microcomputer operates all the essential pumps, solenoid valves, and the dispensing apparatus according to programmed instructions. A predetermined amount of the mixed phytoplankton is apportioned to each culture vessel and the lines are automatically rinsed with hot fresh water before the next cycle.
377 overflow
rtondpipe
“...._,
holes
a+...”
“‘-..~-.
opaque
inspection
cover,
flap.,., ‘..
\water in
desired W*+H level
overflow
foam ..charcoal
hose
or sand
rupport~
\perforated fiberglass
corrugated roofing
drain
Fig. 1. Two versions of the false-bottom culture tank. Arrows indicate direction of water flow. (A) 150-l fiberglass tank with internal overflow. The tank is drained by pulling out the overflow standpipe. (B) 500-l asbestos-cement tank with external overflow. The tank is drained by dropping the external hose to the ground.
3. Retention of cultured organisms (a) False-bottom tanks Fig. 1. These culture tanks are versions of the vessels used to rear marine fish larvae (Brownell, 1979). A nylon mesh of 60-300 pm pore size is firmly attached to the tank walls with a non-toxic adhesive. Either a l-3-cm layer of carbon sand (0.5-1.5 mm diameter) or a &cm sheet of polyurethane foam overlies the nylon mesh. The sand and foam are porous enough to allow detritus to be drawn into the interstitial spaces where it is less likely to come in contact with the animals being cultured. They greatly prolong the length of time the underlying mesh can be left in the tank without fouling. Culture tanks presently employing this retention system range in volume from 25 to 450 1.
mriridgc filter
......
lid
-
JL
Fig. 2. Hoist-transfer tanks. (A) The 150-l tank on the left is being drained into an identical clean tank on the right via the connecting hose. The suspended tanks of the upper tier are not shown. (B) Side view of rear of tank showing arrangement of overflow system employing a 30-50-pm filter cartridge.
319
(b) Hoist-transfer tanks (Fig. 2 ) , In these tanks detritus is allowed to settle onto the otherwise clean, bare tank bottom. Overflow water is screened by a replaceable, washable, pleated cartridge filter of nominal 30-50 pm pore size. 4. Tank cleaning (a) False-bottom tank. The advantage of a retention system employing a false bottom with sand or foam is that the tank can be kept in operation for extended periods without cleaning. This may range from 3 weeks (relatively sensitive pelagic marine rotifer Synchaeta hutchingsi) to 6 months (robust estuarine copepod Pseudodiuptomus hessei) . Thorough cleaning of the tank is moderately time consuming because it requires the removal of the culture and washing of the sand or foam. (b) Hoist-transfer tanks. The vertically moveable tank was conceived to facilitate culture transfer and tank cleaning. The tanks are designed to be raised or lowered by means of a winch (Fig. 2A). By connecting a tube between the bottom drain of a dirty tank containing the culture and the drain of a clean tank, and raising the former relative to the latter, the culture is easily and completely transferred to the clean tank. The air and water lines leading to and from the tanks are flexible and long enough so that they can be left intact when the tanks are raised or lowered by cables clipped onto stainless steel tabs. The tabs are welded to stainless steel plates bonded into the fiberglass tank walls. The transfer hoses are equipped with self-sealing garden snap fittings and no tap is required at the bottom of the tanks. After use, the transfer hoses are rinsed with hot water and hung to dry. Air and water valves are attached to a board mounted on the wall behind the tanks. Each incoming water line is equipped with a medical intra-venous drip chamber mounted on the same board. The water flow to each tank can be checked at a glance and adjusted if necessary without opening tank lids. Air is released at the lowest point in the tank as a slow stream of large bubbles. The overflow filter cartridge is arranged as shown in Fig. 2B. Because of limited space in the temperature-controlled room in which this system is operating, the tanks are square, rather than round, and are arranged in two tiers. Each tier is comprised of 11 tanks. The lower tier consists of 1501 tanks which rest on the floor, the upper tier consists of 60-l tanks that are suspended from an overhead girder. Only the lower tier is shown in Fig. 2A. Any of the lower tanks can be raised and any of the upper tanks can be lowered when a culture is to be transferred. One tank in each tier is kept empty at all times and cultures are routinely transferred between tanks according to a predetermined schedule, typically on a 2-6-week cycle.
380 TABLE 1 List of species that have been cultured in the false-bottom tanks. All fish species listed were reared from the egg through metamorphosis. All non-piscean zooplankton listed were cultured through multiple generations TELEOSTEI Clupeidae Etrumeus whiteheadi Sardinops ocellatus Engraulidae Engraulis capensis Scomberesocidae Scomberesox saurus Gadidae Gaidropsarus capensis Soleidae Heteromycteris capensis Synaptura kleini Cynoglossidae Cynoglossus capensis Carangidae Trachurus trachurus Centracanthidae Pterosmaris axillaris Syngnathidae Hippocampus capensis
Sparidae Chrysoblephus laticeps Diplodus sargus Diplodus cervinus Gymnocrotaphus curvidens Lithognathus mormyrus Pachymetopon blochi Argyrozona argyrozona Pterogymnus laniarius Mugilidae Mugil cephalus Scorpaenidae Coccotropsis gymnoderma Congiopodidae Congiopodus spinifer Triglidae Trigla capensis Atherinidae Atherina breviceps Amphiprionidae Amphiprion percula
COPEPODA Calanidae Calanus finmarchicus australis Calanus carinatus Canthocalanus minor Paracalanidae Paracalanus scotti Temoridae Temora discaudata Centropagidae Centropages brachiatus Pseudodiaptomidae Pseudodiaptomus hessei P. serricaudatus Acartiidae Paracartia africana Acartia natalensis Pseudocyclopidae Pseudocyclops xiphiphorus
Cyclopidae Halicyclops dedeckeri Oithonidae Oithona nana Oithona similis Cyclopinidae Cyclopina sp. Cletodidae Cletocamptus trichotus Tisbidae Tisbe holothuriae Longipediidae Longipedia weberi Tachidiidae Euterpina acutifrons Harpacticidae Tigriopus aff. californicus
381
TABLE I (continued) BRANCHIOPODA Sididae Pen&a avirostris Artemiidae Artemia salina
AMPHIPODA Ceinidae Austrochiltonia subtenuis Eusiridae Paramoera capensis
OSTRACODA Cypridopsidae Sarscypridopsis S. sp. B
CILIATA Strobilidiidae Strombidinopsis sp. Codonellidae Tintinnopsis beroidea Tintinnidae Eutintinnus tubulosus Metacylididae Metacylis jorgenseni Helicostomella subulata Undellidae Proplectella pentagona Climacostomatidae Fabrea salina Condylostomatidae Condylostoma sp. Strombidiidae Strombidium sp. Ptychocylididae Favella campanula F. serrata
sp.A
ROTIFERA Brachionidae Brachionus plicatilis Euchlanidae Colurella colurus C. dicentra Synchaetidae Synchaeta hutchingsi S. vorax
RESULTS
Twenty-five species of marine fish have been reared to date from the egg through metamorphosis in the false-bottom tanks ( Table 1) . Many more were reared well beyond the first-feeding stage. Forty-two species of crustaceans, rotifers, and ciliates have been taken through multiple generations in the falsebottom tanks. At the time of this writing the hoist-transfer tanks have been in operation for 4 months and only seven species have been tested during that time. All were successfully cultured through multiple generations with low maintenance: Calunus finmarchicus australis, Paracalanus scotti, Centropages brachiatus, Pseudodiaptomus hessei, Paracartia africana, Acartia natalensis, and Brachionus plicatilis. DISCUSSION
Nearly all rearing and culture systems described in the literature involve significant continuous or periodic water renewal. Some experimentalists, how-
382
ever, have successfully reared or cultured marine zooplankton, including fish larvae, in relatively small volumes with little or no water exchange over extensive periods. Lasker et al. (1970) kept early larvae of northern anchovy (Engruulis mordax) for 5 weeks in static, 10-l containers. Hettler (1981) reared Atlantic menhaden (Brevoortia tyrannus) for the first month under static conditions. Klein Breteler (1980) cultured several marine copepod species over periods of at least 3 weeks in static containers. There are many other examples. The practice of rearing marine zooplankton in the presence of healthy and actively growing phytoplankton (Struhsaker et al., 1973) may pertain here. In the above examples, Hettler (1981) conducted his rearing in the presence of Chlorellu, Lasker et al. (1970) in the presence of the autotrophic dinoflagellate Gymnodinium splendens, and Klein Breteler (1980) in the presence of the heterotrophic dinoflagellate Oxyrrhis marina. It is possible that ChZoreZZu, Gymnodinium splendens, Oxyrrhis marina, and certain other species of autotrophic and heterotrophic microplankton can create beneficial conditions in a static rearing tank that might otherwise only be approached via water exchange or frequent tank cleaning. The development of microbial slimes on the surfaces of objects exposed to sea water is a widely recognized phenomenon ( ZoBell, 1972; Fletcher and Marshall, 1982). The factors that control the species composition and ecological succession of these slimes (through predator-prey interactions, competition for space and nutrients, ectocrine release, etc. ) are poorly understood. Nevertheless, it has become apparent to the present authors that microbial slimes can have deleterious effects on cultured animals, and that one way to reduce their effects is to physically remove the slimes or to transfer cultures to clean tanks at frequent intervals. Another way to reduce their effects seems to be to maintain healthy populations of certain species of microplankton in the tank. Part of the beneficial effect of the microplankton may be to biologically control populations of deleterious free- or substrate-living organisms. The volume of culture that can be accommodated in the false-bottom and hoist-transfer tanks is limited for practical reasons. In the former, a very large tank requires a correspondingly large amount of bottom sand, which must be cleaned each time the tank is renewed. In the latter, a restriction is placed on the size of tank that can be conveniently raised or lowered. Nevertheless, for specific purposes, intermediate-size tanks may be ideal. For fish larvae the false-bottom tanks are appropriate when relatively small numbers ( ~5000) of eggs are available. The entire larval stage may be passed without cleaning the tank or even removing dead larvae. For pelagic copepods, rotifers, and ciliates, the hoist tanks are particularly suited for long-term maintenance of stock cultures. The animals may be periodically transferred to much larger tanks for batch-culture mass production, as is done at the Sea Fisheries Research Institute laboratory. High copepod densities were achieved using the equipment described above.
383
In hoist-transfer and false-bottom tanks with continuous water flow, cleaned every 2 and 3 weeks, respectively, the copepods Puracartia africana, Parucalanus scotti, and Pseudodiaptomus hessei attained densities over 1000/l, of which at least 20% were adults. P. scotti attained a density of 1750/l in a 150-l falsebottom tank. In static systems using Oxyrrhis marina (Klein Breteler, 1980)) copepod densities were much lower (20-40/l). The ideal, medium-size culture system for marine zooplankton is no doubt still in the future. When it is finally developed, it will very possibly employ continuous water exchange as well as one or more biological measures to control deleterious microbial ectocrines.
REFERENCES Brownell, C.L., 1979. Stages in the early development of 40 marine fish species with pelagic eggs from the Cape of Good Hope. Ichthyol. Bull. J.L.B. Smith Inst. Ichthyol., 40: 84 pp. Fletcher, M. and Marshall, K.C., 1982. Are solid surfaces of ecological significance to aquatic bacteria? In: K.C. Marshall (Editor), Advances in Microbial Ecology, vol. 6. Plenum Press, New York, NY, pp. 199-236. Hettler, W.F., 1981. Spawning and rearing Atlantic menhaden. Prog. Fish-Cult., 43 (2): 80-84. Kinne, O., 1976. Cultivation of marine organisms: water-quality management and technology. In: 0. Kinne (Editor), Marine Ecology, Cultivation, Vol. 3 (1). Wiley, London, Chapter 2, pp. 19-300. Kinne, O., 1977. Cultivation of animals. 5.1. Research cultivation. In: 0. Kinne (Editor), Marine Ecology, Cultivation, Vol. 3( 2). Wiley, London, Chapter 5, pp. 579-1229. Klein Breteler, W.C.M., 1980. Continuous breeding of marine pelagic copepods in the presence of heterotrophic dinoflagellates. Mar. Ecol. Prog. Ser., 2: 229-233. Lasker, R., Feder, H.M., Theilacker, G.H. and May, R.C., 1970. Feeding, growth and survival of Engraulis mordax larvae reared in the laboratory. Mar. Biol., 5: 345-353. Struhsaker, J.W., Hashimoto, S.M., Girard, S.M., Prior, F.T. and Cooney, T.D., 1973. Effect of antibiotics on survival of carangid fish larvae (Cananz mate) reared in the laboratory. Aquaculture, 2: 53-88. ZoBell, C.E., 1972. Substratum: bacteria, fungi and blue-green algae. In: 0. Kinne (Editor), Marine Ecology, Environmental Factors, Vol. l(3). Wiley, London, pp. 1251-1270.