Hormonal sex inversion in striped bass and white bass x striped bass hybrids

The goal of the study was to determine the optimal androgen treatment to produce sex inversion in striped bass Morone saxatilis and white bass M. chrysops x striped bass hybrids. The androgen 17 alpha-methyltestosterone (MT) was orally administered to fish with a dry diet or with nauplii of brine shrimp Artemia sp. for 30 or 40 d within 33-132 d after hatching (d.a.h.). The sex ratios in all of the control groups were close to 1:1. In MT-treated groups, the proportions of males varied from 59% to 100%, depending on the timing of hormone administration. The following regimes of MT-treatment are recommended for practical application: for hybrids, feed fish with a dry diet containing MT at 30 mg/kg from 92-98 d.a.h. through 128-132 d.a.h.; for striped bass, feed fish with a dry diet containing MT at 30 mg/kg from 63 through 93 d.a.h. Histological analysis revealed that inverted males primarily developed testes with some morphological features of ovaries. With further development, the gonads of inverted males transformed towards normal testes.