Sex differentiation and early sex identification in hatchery produced greater amberjack (Seriola dumerili) reared in sea cages

Abstract The histological process of gonadal differentiation together with the endocrine changes of glucocorticoids and sex steroids was studied in hatchery produced greater amberjack (Seriola dumerili) from 101 until 408 days post-hatching. In the samplings, which were conducted every 50 days, no size dimorphism was observed between the sexes and sex ratio was 1:1, suggesting that there was no influence of early rearing in captivity on sex differentiation. Plasma concentrations of cortisol, cortisone, adrenosterone (Ad), androstenedione (Δ4), 11-ketotestosterone (11ΚΤ), testosterone (Τ), estradiol (Ε2), progesterone (P4) and 17,20β-dihydroxyprogesterone (DHP) were measured in males and females with the use of liquid chromatography tandem mass spectrometry (LC-MS/MS) to examine their role in the sex differentiation process. From the nine hormones, the only one that exhibited differences between the sexes was 11-KT. However, variations were observed in the mean values of cortisol, Ad, Δ4, 11-KT, T, P4 and DHP over time in one or both sexes, indicating their involvement in the sex differentiation process. Moreover, the 11-KT/E2 ratio was found to be a useful diagnostic biomarker for greater amberjack sex, from as early as 150 dph.