Induction of sex inversion in common snook (<i>Centropomus undecimalis</i>) males, using 17-β oestradiol implants

Abstract

The common snook (Centropomus undecimalis) is a protandric hermaphrodite fish that has potential for aquaculture due to its high value and market acceptance. One of the difficulties to its reproduction in captivity is that females are older and bigger than males. The objective of this study was to use 17-β oestradiol (E2) hormone implants to induce sex inversion in adult males. Fish with an initial body weight of 383 ± 83 g (mean ± SD), individually tagged were used in the experiment. Four E2 dosages (n = 7) were tested (0.5, 1.0, 4.0 and 8.0 mg kg−1) in Ethylene-vinyl-acetate (EVAc) implants, and a control group (n = 7) implanted without hormone. The parameters evaluated were: survival, weight gain, hepatosomatic and gonadosomatic indices (GSI and HSI) and plasma levels of testosterone (T) and 17-β oestradiol (E2). Also, liver and gonad morphology was observed through histological sections. GSI was higher in E2 treated than in control fish. All E2 treated fish had completely developed ovaries with oocytes at the perinucleolar stage, while all fish in the control group remained males with evidence of active spermatogenesis. After 15 days, plasma levels of E2 were correlated with the hormone dosage. T levels in the control group were higher than in E2 treated fish, at all sampling times. In conclusion, 0.5 mg kg−1 of E2 in EVAc implants is effective to induce sexual inversion in common snook males, which could be useful to obtain broodstock females smaller than in the wild in a reduced time.