Identification of gender and reproductive maturity in the absence of gonads: muscle tissue levels of sex steroids and vitellogenin in gag (Mycteroperca microlepis)
Sa. Heppell et Cv. Sullivan, Identification of gender and reproductive maturity in the absence of gonads: muscle tissue levels of sex steroids and vitellogenin in gag (Mycteroperca microlepis), CAN J FISH, 57(1), 2000, pp. 148-159
Citations number
42
Categorie Soggetti
Aquatic Sciences
Journal title
CANADIAN JOURNAL OF FISHERIES AND AQUATIC SCIENCES
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.