Assessing the feasibility of exogenous 17β-estradiol for inducing sex change in white snook, C. viridis: From growth, resting and maturation studies

Abstract

This study evaluated growth, survival, and oogenesis before and after 17β-estradiol (E2) treatments. During the growth period, C. viridis reached a total length of 65 ± 4.2 cm and a weight of 2.5 ± 0.66 kg BW. To induce sex change in males, we implanted silastic tubing loaded with 0 (control), 0.5, or 1.5 mg of E2 kg−1, at days 0, 30, 60, and 90. Blood samples were collected before treatment (day 0) and on days 30, 60, 90, and 120. Initially, 23% of the selected males expressed milt. At 60 days post-treatment 13% in the control and 4.3% in both, 0.5 and 1.5 mg E2 kg−1 BW treatments. After 120 days we observed histological evidence of sex change in 50% of the histology-tagged fish in the 1.5 mg E2 kg−1 treatment. The gonadosomatic index and condition factor did not differ significantly (P > 0.05) between the control and the treatments. However, the mean individual fish weight differed significantly across all sampling times (P < 0.05). The control and 1.5 treatment groups had a 100% survival rate, while the 0.5 treatment showed a 95.6% survival rate. Steroid profiling showed high cortisol levels throughout the experiment but there was no relationship with E2 treatment or sampling point. After the first E2 dose, we observed inhibition of 11-ketotestosterone (11-KT), which persisted until the end of the experiment. At the end of a 150-day rest period, biopsy samples from the fish showed 0%, 29%, and 87% of females with primary growth oocytes in the control, 0.5, and 1.5 treatments, respectively. After 353 days of the maturation period, feminized fish did not reach vitellogenesis. The availability of C. viridis vitellogenic females after induced sex change remains unpredictable. More research is needed to encourage vitellogenesis in hormonally feminized fish of this species.