Efficacy of two exogenous hormones (GnRHa and hCG) for induction of spontaneous spawning in captive yellowfin bream, Acanthopagrus australis (Sparidae) and influence of sex ratio on spawning success

Yellowfin bream (Acanthopagrus australis) are considered a prime candidate for aquaculture and for release into estuaries to enhance wild stocks and recreational fishing along much of the east coast of Australia. The acclimation of wild yellowfin bream to captivity and the development of reliable protocols for inducing consistent multiple spawns for the mass production of larvae have not previously been reported. Four replicate trials were conducted to assess the efficacy of gonadotropin releasing hormone analogue (GnRHa) and human chorionic gonadotropin (hCG), to induce spontaneous spawning. In each trial, females were injected with a single dose of either saline (control), GnRHa (25, 50, 75, 100μgkg−1) or hCG (250, 500, 750, 1000IUμgkg−1). Control fish did not spawn, whereas treatment with either GnRHa or hCG induced spawning. However, the number of spawns and eggs produced from hCG treated females was not statistically significant from controls. Treatment with GnRHa at a dose of 75μgkg−1 resulted in the most consistent spawning response with both the mean number of spawns (3.0±0.0 SD) and eggs produced (755,000±152,000 SE) significant elevated from controls. However, the quality of eggs from GnRHa treated fish was variable. Egg fertilization rates of the first spawns from GnRHa and hCG treated females were inversely related to latency period, indicating that delayed spawning resulted in poor quality eggs. A second experiment was performed to examine if improvements in the quality of eggs from females (injected with GnRHa at a dose of 75μgkg−1) could be achieved by increasing the number of males placed with a single female. When a 3:1 male to female spawning ratio was used, the proportion of fertilized egg spawned improved over females spawned with a single male.