Gag (Mycteroperca microlepis) are often landed eviscerated, so their gonads are not available for histological verification of gender and stage of maturity. Information on gender is particularly important for the management of hermaphroditic grouper, where increased mortality through fishing can directly affect sex ratio and therefore the reproductive capacity of the population. Alternative techniques for evaluating fish gender and maturity therefore need to be developed for gag and other grouper. We utilized sensitive immunoassays to measure levels of the sex steroids estradiol-17beta (E2), testosterone (T), and 11-ketotestosterone (11KT) and the egg-yolk precursor vitellogenin (VTG) in gag on a quarterly basis. Plasma and muscle levels of E2, T, and VTG in females were lowest during summer, rising in winter to 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 useful for differentiating between males, adult females, and immature fish between December and April, the period of active gonadal recrudescence. This technique should prove useful in cases where fishery data are primarily collected through port sampling and gonads are not available for analysis.
Pituitary–ovarian axis during lactational amenorrhoea. I. Longitudinal assessment of follicular growth, gonadotrophins, sex steroids and inhibin levels before and after recovery of menstrual cyclicity
