Progress in controlled breeding of Nassau grouper ( Epinephelus striatus) broodstock by hormone induction

Abstract

Human chorionic gonadotropin (HCG), luteinizing hormone-releasing hormone analogue (LHRH-a), and carp pituitary homogenate (CPH), used alone or in various combinations, were tested as spawning agents in captive E. striatus broodstock. Fifty hormone-induced strip-spawning trials were attempted using a two-injection sequence in which a priming dose (PD) was followed 24 h later by a resolving dose (RD). Hormone treatment strategies tested included, HCG alone (PD = 1000 IU kg −1 bw, RD = 500 IU kg −1 bw), LHRH-a alone (PD = 50–100 μg kg −1 bw, RD = 100–200 μg kg −1 bw), HCG (500 IU kg −1 bw) in combination with LHRH-a (50–100 μg kg −1 bw) as priming or resolving doses, and CPH (PD = 10 mg kg −1 bw) in combination with LHRH-a (RD = 50–100 μg kg −1 bw). As an alternative to hormone injection, intramuscular implantation of a cholesterol pellet containing LHRH-a (200–250 μg) was tested in two females. Females with mean oocyte diameters ranging from 482 to 561 μm were suitable for hormone-induced spawning. Oocyte diameter increased to 524–708 μm within 24 h of the priming dose and to 852–945 μm within 9–16.4 h following the resolving dose. Average diameter of spawned (water hardened) eggs ranged from 879–978 μm. Although fertilization rate (0–94.7%) varied widely among trials, successful spawnings (fertilization rate ≥ 50%) were obtained in all of the hormone strategies tested. Use of different hormones in combination showed no advantage over a single-hormone strategy. As HCG appeared to cause an immune response, LHRH-a is recommended for repeated application. Implantation of LHRH-a produced variable results, inducing ovulation in one female, but apparently inducing sex reversal in the other.