This study aimed to document the seasonal cycle of steroid levels in the plasma and ovary, including testosterone (T), estradiol-17β (E2) and 17α, 20β-dihydroxy-4-pregnen-3-one (DHP) in relation to ovarian development in wild populations of female blue tang fish. The gonadosomatic index (GSI%) maintained high values from April to July and increased from the II to IV ovarian stages and dropped in the V stage. Levels of plasma, ovary T and E2 and DHP were high from March to July. Plasma T and E2 levels were low in the II stage when most oocytes were previtellogenic, reaching a peak during spawning, and decreased in the V stages when fish were going to late spawning and termination. DHP was detected in all stages of the ovary with a higher level in spawning fish but decreased after spawning. These results revealed that T, E2 and DHP could be involved in ovarian development and DHP may play a significant role as a maturational inducing hormone in blue tang fish.
Keywords: ELISA; GSI; ovarian development; steroid hormones; wild blue tang.