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Induced Spawning of F1 Wreckfish (Hāpuku) Polyprion oxygeneios Using a Synthetic Agonist of Gonadotropin-Releasing Hormone

Wild-caught hāpuku (Polyprion oxygeneios) spawn readily in captivity, but although first filial (F1) hāpuku 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 hāpuku 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 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 hāpuku in captivity by strip-spawning.