Sex identification in captive hapuku (Polyprion oxygeneios) using ultrasound imagery and plasma levels of vitellogenin and sex steroids

Identifying the sex of captive fish is crucial to aquaculture broodstock management. Hapuku (Polyprion oxygeneios) are sexually monomorphic fish that are reared in New Zealand as a potential aquaculture species. In order to identify the sex of 23 F1 captive hapuku, three methods, namely ultrasound imaging, plasma vitellogenin (Vtg) enzyme-linked immunosorbent assay (ELISA) and plasma sex steroid (17β-estradiol (E2) and 11-ketotestosterone (11-KT)) radioimmunoassay (RIA), were compared. Results suggest that all three methods may be used two months prior to- and during the -spawning season of adult captive broodstock (which occurs between August and December) when used on sexually developing fish. Furthermore, ultrasound and RIA showed the potential to identify the sex of sexually undeveloped fish. Only repeated ultrasound scans allowed for very high sex identification accuracy (95%). Vtg analysis yielded a 92% positive identification of samples but there was a narrow cut-off margin between males and females (relative absorbance values: 0.0043–0.022). However, compared to RIA, this method allowed a larger number of samples to be tested. The sex steroid ratio method using RIA was more accurate (100%) and robust than the Vtg analysis as the cut-off margin between males and females was more distinct (11-KT/E2 ratios of between 0.17 and 0.83). Overall, a combination of the methods provides validation and increases the accuracy of identification. This paper also provides the first evidence of the sexual development of captive reared hapuku.

► Hapuku (Polyprion oxygeneios) is a new aquaculture species in New Zealand.
► Ultrasound, plasma levels of Vtg and steroids were used to identify sex of hapuku.
► All methods successfully identified the sex of sexually developing F1 fish.
► The ratio of the sex steroids 11-KT/E2 was the most accurate and robust method.
► This is the first report on sexually developing farmed F1 hapuku.