Hormone Treatment Efficacy for Induction of Spawning Captive Yellowfin Bream ('Acanthopagrus australis') and the Effect of Salinity on Egg Fertilization Hatching, and Early Larval Development

Abstract

This study assessed the efficacy of two exogenous hormones, gonadotropin releasinghormone analogue (GnRHa) and human chorionic gonadotropin (hCG) to induce spermiation and spontaneous spawning in captive yellowfin bream 'Acanthopagrus australis' (Sparidae). The effect of activating gametes at different salinity levels on egg fertilization, hatching, larval development and survival was also examined to determine the feasible salinity range of water that could potentially be used by hatchery operators for spawning in captivity, egg incubation and early larval rearing until the time of first feed. Adult yellowfin bream underwent gametogenesis in captivity and by the onset of the natural spawning season males were sperimating and females had developed vitellogenic oocytes. Males and females were injected on a body weight (bw) basis with either saline (control) or a single dose of either GnRHa (25, 50, 75, 100 μg kg⁻¹) or hCG (250, 500, 750, 1000 IU kg⁻¹). Milt and blood samples were collected from males to assess the effects of hormone treatment. Males did not respond to saline or treatment with hCG. Whereas, treatment with GnRHa at a dose of 100 μg kg⁻¹ bw significantly increased milt volume at 48 hours post injection (h p.i). The cumulative number of sperm produced by the 100 μg kg⁻¹ bw over the 48 h sample period was also significantly elevated. In contrast to saline and hCG treated males, all GnRHa treatment groups had elevated plasma levels of and 11-ketotestosterone (11-KT) by 24 and 48 h p.i. Levels of testosterone were not elevated among treatment groups. These results suggest that as for other teleosts, gonadotropin-dependent production of 11- KT is the major mediator of spermatogenesis in the yellowfin bream.