The use of luteinizing hormone releasing hormone analogue for ovulation induction in black sea bass (Centropristis striata)

Interest in commercial production of black sea bass has increased in recent years, but reliable spawning methods remain problematic. The objective of this study was to evaluate the effects of oocyte size and luteinizing hormone releasing hormone analogue (LHRHa) dosage and delivery systems on ovulatory success for in vitro fertilization. Vitellogenic females with maximum oocyte diameters of 400-625 μm were implanted with a 95% cholesterol-5% cellulose pellet containing 50 μg of LHRHa. Fish with maximum oocyte diameters < 450 μm failed to ovulate. In contrast, 90% of fish with 500 μm oocytes spawned within 36 h and 40% of this group ovulated a second time. All of the females containing oocytes > 550 μm ovulated. In a second experiment, females with uniformly vitellogenic oocytes (> 500 μm) and implanted with 50 μg LHRHa ovulated substantial numbers of eggs (45,000-192,000 eggs/kg body weight (BW), but fertility was consistently low (0-15%). In a third experiment, 19 of 39 females receiving implants containing 6.3-23.6 μg LHRHa/kg BW during the spawning season ovulated, but fecundity (17,000-339,000 eggs/kg) and fertilization (0-98%) were highly variable. When fish were grouped by developmental index, calculated as the number of oocytes with diameters > 400 μm/total number of oocytes measured, there were no statistical differences among groups with respect to the number of spawns, fecundity or fertilization success. In a fourth experiment, 11 of 13 females with a clutch of fully vitellogenic oocytes that were injected with 20 or 100 μg/kg BW LHRHa ovulated between 1 and 2 times on consecutive days. Five of seven given an implant containing 12.5 μg LHRHa ovulated one or more times. Fish implanted with shams or injected with vehicle alone did not ovulate in any of the experiments. No differences were found in the number of spawns, fecundity or fertilization success from fish receiving different doses of injected or implanted LHRHa. Incubation of pooled eggs produced 155,000 larvae (60% hatch) and 95,000 one-gram juveniles. These results demonstrate that injected or implanted LHRHa is effective for inducing ovulation in black sea bass with maximum oocyte diameters > 500 μm.