| Summary: | Monosex stocks of fish become increasingly important in the aquaculture. In fish with male heterogamety, mating females with neo-males i.e. hormonally sex reversed (masculinized) females results in “all-female” stocks. Masculinization is usually performed by administration of androgens such as 11β-hydroksyandrostenedione (OHA) to fish before or during their gonadal differentiation process. The main goal of the present research was to evaluate efficiency of OHA diet supplementation applied for the sex reversion in whitefish. Whitefish larvae 32 days post hatching (DPH) with body weight of about 0,096 (±0,031) g were reared in four groups: fish fed with 10 ppm of OHA (OHA10), fish fed with 20 ppm of OHA (OHA20) and fish fed without OHA (C1, C2). Fish from OHA10, OHA20 and C1 groups were reared in the separate RASs while fish from C2 group were reared in water from OHA20 group. The treatment with OHA lasted 9 weeks. During subsequent 12 weeks all fish were fed without any supplementation of OHA. 30 individuals from each group were then randomly chosen for the histological analysis. No gonadal females were found among sampled fish from any of OHA groups. Gonadal males constituted of 60% and 47% of the sampled fish from OHA10 and OHA20 groups, respectively. About 23% of the fish from OHA10, OHA20 and C1 and 47% of specimens from C2 were intersexual. Moreover, 27% of the fish from OHA20 were sterile. Lack of the females among fish from OHA groups suggested OHA disturbed growth and development of ovaries in whitefish. However, a very high percentage of the sterile fish in the OHA20 group indicated application of lower doses of OHA for masculinization of the whitefish. Unexpectedly high percentage of intersexual fish especially in both control groups suggested disturbances in the sexual differentiation process triggered by the environmental and genetic factors.
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