Identification of gender and reproductive maturity in the absence of gonads: muscle tissue levels of sex steroids and vitellogenin in gag (Mycteroperca microlepis)

Gag (Mycteroperca microlepis) are often landed eviscerated, so their gonads are not available for histological verification of gender and stage of mat urity. Information on gender is particularly important for the management o f hermaphroditic grouper, where increased mortality through fishing can dir ectly affect sex ratio and therefore the reproductive capacity of the popul ation. Alternative techniques for evaluating fish gender and maturity there fore need to be developed for gag and other grouper. We utilized sensitive immunoassays to measure levels of the sex steroids estradiol-17 beta (E-2), testosterone (T), and 11-ketotestosterone (11KT) and the egg-yolk precurso r vitellogenin (VTG) in gag on a quarterly basis. Plasma and muscle levels of E-2, T, and VTG in females were lowest during summer, rising in winter t o reach peak values in spring. During winter and spring, plasma and muscle levels of 11KT were significantly higher in males than in adult females or immature fish. Combined measurement of VTG and 11KT in gag muscle proved us eful for differentiating between males, adult females, and immature fish be tween December and April, the period of active gonadal recrudescence. This technique should prove useful in cases where fishery data are primarily col lected through port sampling and gonads are not available for analysis.