Induced Spawning of F1 Wreckfish (Hapuku) ¯ Polyprion oxygeneios Using a Synthetic Agonist of Gonadotropin-Releasing Hormone
Wild-caught hapuku ( ¯ Polyprion oxygeneios) spawn readily in captivity, but although first filial (F1) hapuku complete vitellogenesis, females fail to undergo oocyte maturation and spawn or produce poor quality eggs. This study investigated whether administration of a synthetic agonist of gonadotropin-releasing hormone (GnRHa) could improve F1 hapuku spawning and complete the life-cycle in captivity. Spawning trials were conducted over 2 years in 2013 and 2014, when F1 were aged five and six
... aged five and six years. In 2013, females previously conditioned under a variable or constant temperature regime were implanted with GnRHa (100 µg/kg−1) or blank implants constructed of powdered cellulose and cholesterol. Spawning was erratic and egg quality very poor in all tanks. No F2 offspring were produced by communal spawning. In contrast, viable F2 larvae were produced by strip-spawning and in vitro fertilization after a series of GnRHa injections. In 2014, two additional trials were conducted: females received ethylene-vinyl acetate copolymer (EVAc) matrix implants containing GnRHa (100 µg/kg−1) or blank implants and in the second trial, two GnRHa doses (100 µg/kg−1 and 50 µg/kg−1) were tested. Eggs were first detected in all tanks 12–17 days post-implantation when females received 100 µg/kg−1 GnRHa implants, but not in the lower dose or control tanks. In summary, this study achieved induction of female spawning with GnRHa implants (target dose 100 µg/kg−1) and the successful production of F2 hapuku in captivity by strip-spawning.