The use of gonadotropin-releasing hormone analogue (GnRHa) to induce reproduction in captive yellowbelly flounder (Rhombosolea leporina)

Abstract Recent interest in aquaculture of the endemic New Zealand yellowbelly flounder (YBF) has highlighted the need to develop hatchery technology for this species. However, knowledge of the reproductive biology of YBF is limited, and controlled reproduction in captivity is yet to be established. Previous work indicates that wild-caught YBF commonly fail to adapt to captivity and exhibit high mortality post capture. In this work, a pilot investigation to induce reproduction in wild fish caught at the onset of the breeding season was conducted. Twenty-seven wild-caught adult females and 12 males were placed into indoor tanks. Females were administered either a sham (saline) or gonadotropin-releasing hormone analogue (GnRHa) treatment (50 µg kg −1 or 100 µg kg −1 ). Ovulation only occurred in GnRHa-treated fish with the greatest response in the 50 µg kg −1 group (3 ovulations detected versus 1 in the 100 µg kg −1 group). Compared to controls, fish in the 50 µg kg −1 treatment completed final oocyte maturation (FOM) to produce hydrated oocytes ( p < 0.02). Fertilisation rates in excess of 80% were achieved in fish from both the 50 and 100 µg kg −1 GnRHa treatments via in vitro fertilisation using pools of motile sperm, suggesting that high quality gametes may be achievable using hormone-induced reproduction. In contrast, control fish appeared to arrest oocyte development at FOM. These results indicate that induction of maturation using GnRHa could be a viable methodology to support the hatchery production of wild YBF caught at the end of the pre-spawning season until captive acclimated broodstocks are available.