TECHNICAL NOTES Spawning Frequency and Egg ...

The Progressive Fish-Cullurist 58:140-142. 1996 **' Copyright by the American Fisheries Society 1996

TECHNICAL NOTES Spawning Frequency and Egg Production of Captive Spotted Seatrout BRIAN B. WISNER,' KRISTIN L. MERTZ, AND THOMAS R. CAPO2 University of Miami Experimental Hatchery Kosenstiel School of Marine and Atmospheric Science 4600 Rickenbacker Causewav. Miami, Florida 33149. USA Abstract,—Nine mature spoiled sealroul Cynoscion nebulosus (seven females and iwo males) were placed in a recirculaiing-waier culture system al the University of Miami Experimental Halchery in July 1993. Photoperiod and water temperature were maintained at 14 h light: 10 h dark and 27.5°C. Spotted seatrout held in this controlled photo-thermal culture system spawned on 172 occasions between August 1. 1993, and April 22. 1994, producing approximately 168 million eggs. On average, spawning occurred every 1.5 d. The 172 spawns during the 265-d spawning period represent an average of 24.6 spawns/female or I spawn/female every 10.8 d. The mean volume of eggs collected per spawn was 306 mL (SD = 215). The estimated average number of spotted seatrout eggs per milliliter was 3.184 (SD = 499). The mean percentage of viable eggs per spawn was 47.5% (SD = 29). Spotted seatroul held in the constant photo-ihermal regime of 14 h light: 10 h dark and 27.5°C consistently produced eggs over a 9-month period. The spotted seatrout Cynoscion nebulosus is an economically important recreational and commercial fish in the Gulf of Mexico and southeastern United States. There has been a growing interest and participation by government agencies in spawning and culturing this species for stock enhancement purposes and by university personnel for using marine fish eggs and larvae for bioassay purposes. Spotted seatrout have been induced to spawn by selected hormone injections (Colura 1974; Tucker 1988; Colura et al. 1989, 1990), dietary administration of hormones (Thomas and Boyd 1989), and conditioning by photoperiod and temperature (Arnold et al. 1978). Successful pond culture of larval spotted seatrout has been reported by Colura et al. (1976, 1992) and Porter and Maciorowski (1984). Although hormone injection is a satisfactory method of spawning fish, the procedure requires a high degree of skill to perform, and it is stressful to the broodstock and typically can only be accom1 Present address: Prince William Sound Aquaculture Corp.. Main Bay Hatchery, Posi Office Box 689, Whittier, Alaska 99693, USA. 2 To whom correspondence should be addressed.

plished during the natural spawning season of the species. Spotted seatrout are highly susceptible to handling stresses (Thomas et al. 1995) associated with hormone injections and strip spawning. Conditioning the fish to spawn through the use of photoperiod and temperature is less stressful to the broodstock, and the fish can be used for successive spawns over a prolonged period. Spotted seatrout are capable of repeated spawning during their natural spawning season (Brown-Peterson and Thomas 1988; Brown-Peterson et al. 1988). The use of photo-thermal-conditioned spawning permits egg production outside a species natural spawning season. Arnold et al. (1978) collected eggs from spotted seatrout for 13 consecutive months after conditioning the fish. Although information is available on spotted seatrout reproduction and spawning (Brown-Peterson and Thomas 1988; Brown-Peterson et al. 1988; Saucier and Bait/ 1992), little is available on the spawning frequency or egg production of spotted seatrout held in photo-thermal conditioning cycles. For pond culture of juvenile spotted seatrout to be successful, it is critical that enough eggs or larvae be available for stocking when zooplankton are abundant in ponds. Additionally, if spotted seatrout eggs and larvae are to be used in bioassay, sufficient quantities of eggs must be available on a consistent basis throughout the year. The objectives of this study were to determine the spawning frequency of spotted seatrout held in a culture system with the photoperiod and temperature regulated to simulate the natural spawning season and to estimate the mean number of eggs per spawning episode. Spotted seatrout were captured by hook and line in August 1992, placed in an outdoor fiberglass raceway (5,000 L) at the University of Miami Experimental Hatchery (UMEH), and held at ambient conditions with flow-through (0.5 turnovers/h) seawater from Bear Cut, Biscayne Bay, Florida. Fish were fed a diet of fro/en squid, fish, and shrimp, supplemented with vitamins. Natural spawning oc-

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FIGURE 1.—Monthly spawning frequency of spotted seatrout (seven females, two males) held for 9 months in a constant photo-thermal regime (14 h light: 10 h dark. 27.5°C) at the University of Miami Experimental Hatchery.

Eggs were skimmed directly from the water surface and passed through a 3.8-cm poly vinyl chloride pipe into a saran sock net (500 u,m mesh) submerged in an aerated 380-L fiberglass tank. Like eggs of red drum Sciaenops ocellatus (Colura 1990), live seatrout eggs float and dead eggs settle to the bottom. Spotted seatrout eggs were placed in a I -L graduated cylinder, and after 20 min, the volumes of living and dead eggs were measured to the nearest milliliter. To estimate the number of eggs per milliliter, 30 samples (0.4-3.8 mL of eggs) from 16 spawns were counted. Water quality during the study was stable and within the ranges reported for natural spawning of

0.3°C (monthly mean ± SD), salinity was 35.4 ± 0.9%r, dissolved oxygen was 5.9 ± 0.1 mg/L, TAN was 0.16 ± 0.04 mg/L, nitrite was 0.02 ± 0.01 mg/ L, and pH was 7.91 ± 0.04. Spotted seatrout held in the culture system spawned on 172 d between August 1, 1993. and April 22, 1994, for an average of one spawn every 1.5 d. The mean monthly spawning frequency (Figure 1) was 19 spawns/ month. It was not possible to determine which individual or how many females spawned on each occasion; however, the 172 spawns represent an average of 24.6 spawns/female or 1 spawn/female every 10.8 d. Using a variety of methods (females running ripe in spawning season, final oocyte maturation, post-ovulatory follicles, and spawning frequency of fish held in controlled laboratory conditions), Brown-Peterson et al. (1988) reported that spotted seatrout spawning frequency in south Texas ranged from every other day to every 3 weeks. In all, 52,673 mL of eggs were collected, although some of the eggs avoided collection by sinking to the bottom of the tank. The mean volume of eggs per spawn was 306 mL (SD = 215). The estimated average number of spotted seatrout eggs per milliliter was 3,184 (SD = 499). The mean percentage of floating (viable) eggs was 47.5% (SD = 29). The mean number of viable eggs per spawn collected during the study was approximately 463,000. Monthly mean number of eggs and the number of viable eggs are presented in Figure 2. Spotted seatrout spawning in the UMEH culture system provided a consistent supply of eggs during the 9-month study period. By having eggs available on a consistent basis, pond managers can stock ponds to coincide with abundant natural food supplies. Successful culture in Texas has been accomplished by stocking ponds with larvae that are 2 d

spotted seatrout (Brown-Peterson et al. 1988; Saucier and Bait/ 1992). The temperature was 27.7 ±

old at rates of 45,000-2,075,000 larvae/ha (Colura et al. 1992). The mean production of approximately

curred in the raceway on several occasions in July 1993. On July 26, 1993, nine spotted seatrout (seven females and two males) were placed in a recirculating-water culture system. Mean weight and total length of the fish were 1.5 kg (SD = 0.25) and 50 cm (SD = 2.5). The broodstock were fed approximately 0.25-1.0 kg of either frozen shrimp, fish, or squid per day, 5 d/week. A vitamin mixture was added to the diet once per week. The system consisted of a 12,000-L circular fiberglass broodstock tank, 736-W centrifugal pump, sand filter, titanium heat exchanger, packed column biological filter, and an egg collector. Photoperiod was set at 14 h light: 10 h dark and temperature was 27.5°C. Temperature, dissolved oxygen, salinity, pH, total ammonia nitrogen (TAN), and nitrite were recorded daily. The sand filter was back washed once a week with tank water. The tank received approximately 1-2 L/min of new incoming water to fill the tank after backwashing and to allow excess surface water to be skimmed into an egg collector.

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FIGURE 2.—Monthly total number of eggs and number of viable eggs collected from spawning spotted seatrout (seven females, two males), held for 9 months in a constant photo-thermal regime (14 h light: 10 h dark, 27.5°C) at the University of Miami Experimental Hatchery.

463,000 eggs/spawning episode in the UMEH culture system would provide sufficient quantities for subsequent pond stocking or use as bioassay organisms. The UMEH culture system was previously stocked with 50-90 kg of red drum broodstock and maintained good culture conditions. If the biomass of spotted seatrout broodstock were increased to a similar level, egg production and spawning frequency might also be increased. Future studies should test other broodstock densities and sex ratios to maximize egg production. Acknowledgments.—The authors thank the South Florida Fishing Classic for funding this study and the South Florida Flats Anglers and the Atlantic Gamefish Foundation for their valuable assistance in capturing and handling the spotted seatrout broodstock. We also gratefully acknowledge the assistance of A. E. Boyd in the daily monitoring of water quality and egg collections and D. Bennetti and J. Serafy for reviewing the draft of this manuscript.

References Arnold, C. R., J. L. Lasswell, W. H. Baily, T. D. Williams, and W. A. Fable, Jr. 1978. Method and techniques for spawning and rearing spotted seatrout in the laboratory. Proceedings of the Annual Conference Southeastern Association of Fish and Wildlife Agencies 30(1976): 166-178. Brown-Peterson. N. J., and P. Thomas. 1988. Differing reproductive life histories between temperate and subtropical groups of Cynoscion nebulosus. Contributions in Marine Science 30(supplemenl):71-78. Brown-Peterson, N. J.. P. Thomas, and C. R. Arnold. 1988. Reproductive biology of the spotted seatrout, Cynoscion nebulosus, in south Texas. U.S. National Marine Fisheries Service Fishery Bulletin 86:373388. Colura, R. L. 1974. Induced spawning of the spotted

seatrout Cynoscion nebulosus (Cuvier). Proceedings of the World Mariculture Society 5:319-330. Colura, R. L. 1990. Hormone induced strip-spawning of red drum. Texas A&M University Sea Grant College TAMU-SG-90-603:33-34. Colura, R. L.. B. T. Hysmith, and R. E. Stevens. 1976. Fingerling production of striped bass (Morone saxatilis). spotted seatrout (Cynoscion nebulosus) and red drum (Sciaenops ocellatus) in saltwater ponds. Proceedings of the World Mariculture Society 7:79-92. Colura, R. L., T. L. King, J. D. Gray, and B. W. Bumguardner. 1992. Analysis of six years of spotted seatrout (Cynoscion nebulosus) pond culture trials. Aquaculture 107:313-332. Colura, R. L., A. F. Maciorowski, and A. HendersonArzapalo. 1989. Gonadal maturation, fecundity and strip-spawning of female spotted seatrout. Proceedings of the Annual Conference Southeastern Association of Fish and Wildlife Agencies 42(I988):8088. Colura, R. L., A. F. Maciorowski, and A. HendersonArzapalo. 1990. Induced spawning of spotted seatrout with selected hormone preparations. Progressive Fish-Culturist 52:205-207. Porter, C. W. and A. F. Maciorowski. 1984. Spotted seatrout fingerling production in saltwater ponds. Journal of the World Mariculture Society 15:222-232. Saucier, M. H., and D. M. Baltz. 1992. Hydrophone identification of spawning sites of spotted seatrout Cynoscion nebulosus (Osteichthys: Sciaenidae) near Charleston, South Carolina. Northeast Gulf Science 12:141-145. Thomas. P., C. R. Arnold, and G. J. Holt. 1995. Red drum and other sciaenids. Pages 118-137 in N. R. Bromage and R. J. Roberts, editors. Broodstock management and egg and larval quality. Blackwcll Scientific Publications, Oxford, UK. Thomas, P., and N. W. Boyd. 1989. Dietary administration of an LHRH analogue induces spawning of spotted seatrout (Cynoscion nebulosus). Aquaculture 80: 363-370. Tucker, J. W., Jr. 1988. Growth of juvenile spotted seatrout on dry feeds. Progressive Fish-Culturist 50:3941.