Biotecnologia Aplicada Elfos Scientiae ISSN: 0684-4551 Vol. 13, Num. 4, 1996

Aquaclture of Red Drum (Siaenops ocellatus)and Other Sciaenids

P Thomas , C Arnold and J Holt

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Introduction

Recent refinements in red drum (Sciaenops ocellatus) aquaculture have led to a rapid increase in commercial production of these species in southern regions of the United States (1). Major advances in the artificial control of reproduction and rearing of red drum larvae and juveniles in captivity are summarized here. In addition, the potential applications of these technologies to the culture of other sciaenid fishes are discussed.

Reproduction

Precocious maturation

The time for red drum to reach sexual maturity can be reduced by more than half by rearing them at summer temperatures (24-28 C) and a constant photoperiod (12L:12D) and feeding them a high food ration (2, 3). Red drum, which normally mature at 4-5 years of age, can be induced to undergo sexual maturation and begin spawning before they are two years old by this technique.

Gonadal recrudescence

Exposure to condensed annual photoperiod and temperature cycles is the preferred method of inducing gonadal recrudescence in all the sciaenid species investigated so far. Environmental manipulation techniques to induce gonadal recrudescence and spawning of sciaenids in captivity were first developed for spotted seatrout (Cynoscion nebulosus) and red drum by Arnold and coworkers. Gonadal growth and spawning of spotted seatrout occurred under summer conditions (15L:9D, 26 C) whereas autumn conditions (9L:15D, 23 C) were required for red drum spawning (4). Condensed (4-6 months) annual cycles are now routinely used to induce gonadal recrudescence in red drum and orangemouth corvina (Cynoscion xanthulus) (5, 6).

Spawning

Special procedures are not usually required to induce spawning of red drum and spotted seatrout; once the gametes are fully developed, the broodstock are maintained at the temperature and photoperiod conditions at which they spawn naturally. Spawning can usually be induced by gradually lowering and then raising the water temperature if it does not occur naturally (2, 5). Once spawning begins, it will continue indefinitely if the fish are held under optimun environmental conditions for spawning up to 7.5 years for one group of red drum broodstock (2). Hormonal treatments are reliable methods of inducing spawning of orangemouth corvina and other sciaenid species that do not respond predictably to environmental manipulation (7). A single injection of a LHRH analog (20-100 ug/Kg bw) induces spawning of a variety of sciaenid fishes 30-36 h later (8). A hormonal method of spawning seatrout, in which LHRHa is administrated in the diet, has been developed to eliminate the stress associated with capture and handling (9). Oral administration of 0.5-1.0 mg LHRHa/Kg bw in the diet (dead shrimp) induced spawning in spotted seatrout 32-38 h later. Spotted seatrout can be induced to spawn repeatedly by oral administration of LHRHa at 20-30 day intervals, the interval required for a new cohort of oocytes to complete their growth. In contrast, oocyte growth and feeding are interrupted for two weeks after each injection of LHRHa resulting in fewer spawns and decreased egg production during the spawning season. Repeated oral administration of a LHRH analog is a valuable method, therefore, for large scale production of spotted seatrout eggs.

Rearing

Larval culture

Sciaenid larvae are easily grown on cultured Brachionus plicatilis and Artemia sp. Microencapsulated diets are readily accepted if they are of appropiate size and can be maintained in the water column, but larvae are unable to obtain sufficien nutrition without the addition of live prey (10). The alimentary canal is simple in first feeding red drum larvae but the digestive glands and measurable concentrations of digestive enzymes are present (11). Larvae can be weaned to dry micro-particulate diets at one week of age with high survial and excellent growth rates (12). Test diets containing 50 % protein and 18-20 % lipid with 2.5-3.5 n-3 HUFA produced the best growth (13). Succesful weaning of red drum larvae from live prey after only one week is unique and of great importance in the development of economical, year-round production of juveniles.

Juvenile Culture

Juvenile red drum can be reared in high-density recerculating systems. Fifty-six day old red drum fingerlings (0.66 g mean weight) were stocked at a density of 307 fish/M^3 into a 38 MT semi-closed recirculation system. After 126 days of culture survival, mean weight and maximum biomass of the system were estimated at 70 %, 73.7 g and 16 Kg/m^3, respectively.

References

Thomas P, et al. In: Broodstock management and egg and larval quality, Bromage NR and Roberts RJ (eds.) 1995;118-137. Blackwell.

Thomas P, et al. Journal of the World Aquaculture Society 1995;25:214-224.

Arnold CR, et al. Contributions in Marine Science 30 (suppl.) 1988;65-70.

Arnold CR, et al. In: Proceedings of the Annual Conference of the Southeastern Association of Game and Fish Commissioners 1976;30:167-178.

Arnold CR, et al. In: Proceedings of the Annual Conference of the Southeastern Association of Game and Fish Commissioners 1977;31:437-440.

McCarty CE, et al. In: The role of fish culture in fishery management,Stroud RH (cd.) 1986;249-262. American Fishes Society.

Prentice Ja, Thomas P. Progressive Fish Culturist 1987;49:66-69.

Thomas P, Boyd NW. Contributions in Marine Science 30 (suppl.) 1988;43-47.

Thomas P, Boyd NW. Aquaculture 1989;80:363-370.

Holt GJ. Journal of the World Aquaculture Society 1992;23:265-270.

Holt GJ, Sun F. European Aquaculture Society Spec Pub 1991;15:30-33.

Holt GJ. Journal of the World Aquaculture Society 1993;24:225-230.

Brinkmeyer RI, Holt GJ. Progressive Fish Culturist 1995;57:30-36.

Copyright 1996 Elfos Scientiae