Masculinization of northern pike fry using the steroid 11 beta-hydroxyandrostenedione

Morphological and histological studies of gonads demonstrated that 11 beta -hydroxyandrostenedione (11 beta -HA) can be used to control the phenotypic sex in northern pike Esox lucius. Oral administration of 11 beta -HA (30 m g/kg pelleted food) to northern pike juveniles (average total length +/- SD = 2.80 +/- 0.18 cm) for 2 weeks resulted in sex reversal of most of the fe males and produced a stock that consisted of 87% males and 13% bisexual ani mals. Testes of hormone-treated fish possessed seminal ducts and were chara cterized by a regular morphology, but histological observations showed that germ cells differentiated earlier in ontogeny than we observed in the gona ds of untreated fish. Gonads of bisexual fish were morphologically ovaries or testes but in either case contained both female and male germ cells, alt hough in some individuals atrophy of individual oocytes was observed. We ob tained practical information on effectiveness of the androgen application ( timing, duration, and dose) to northern pike juveniles.