Sex ratios in offspring of sex-reversed sea bass and the relationship between growth and phenotypic sex differentiation

摘要

Two groups of 60 sexually undifferentiated sea bass (Dicentrarchus labrax) were given 17alpha-methyltestosterone (10 mg/kg) from day 126 to day 226 after fertilization. The percentage of males was increased in comparison with untreated controls (100250L? vs. 79±3%). Spermatozoa from the 13 phenotypic males from the 17alpha-methyltestosterone-treated group were used to fertilize ova from 2 unrelated females. The offspring of each male were reared separately and sampled at 11 and 15 months of age. Females predominated among the larger fish; males and undifferentiated fish predominated among the smaller fish; intersexes were intermediate in size. All fish with body lengths of less than 12 cm were undifferentiated. It is concluded that sex determinationwas more dependent on length than age. At 15 months of age the sex ratios in all families except 1 were male biased. Only 2 families had sex ratios that differed from 1:1. It is concluded that the mechanism of sex determination is not an XX/XY or ZW/ZZ type. It is suggested that environmental factors may act epigenetically on the sex determining mechanisms.