Gonadogenesis in early developmental stages of Acipenser naccarii and influence of estrogen immersion on feminization

Gonad development processes and the effects of a single 8‐hour immersion treatment with 17β‐estradiol (E2, 400 μg L^?1) on sex differentation in the Adriatic sturgeon, Acipenser naccarii, were investigated. After migration of germ cells, gonadal ridges appeared in 16‐ to 18‐day old larvae and undifferentiated gonads in 55‐ to 60‐day old larvae. Putative ovaries with notches in the germinal epithelium and presumed testes with smooth germinal epithelium appeared in 180–185‐day old juveniles. Ovaries with proliferating oogonia and early meiotic oocytes clusters were observed in 292‐day old juveniles. Testes did not exhibit germ cell mitosis until 430 days of age. Developmental stages in E₂‐treated animals closely followed those of controls up to 430 days. The treatment significantly increased the percentage of ovaries when administered to embryos about 1.5 day before hatching, while did not significantly altered the normal 1/1 sex ratio when administered to 1.5‐day old pre‐larvae and 10‐day old larvae. It is likely that in A. naccarii exogenous E₂ administration may act through a feedback mechanism of self‐supporting steroid production and that steroids are the physiological inducers of sex differentiation, as in most teleosts. The E₂‐immersion treatment, easier than time‐consuming administration through food, could be a good approach to control sex differentiation and caviar production.