Inhibition of Spermatogenesis and Vitellogenesis in Rainbow Trout by Hormonal Additives in the Diet

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Abstract
In 1976, groups of rainbow trout (Salmo gairdneri) that were prepuberal males and adult females undergoing their second reproductive cycle were given methyltestosterone (MT) or estradiol (E) in pelleted feed at dosages of 50 or 500 µg/kg of feed (groups offish received each dosage of each hormone) during the period of spermatogenesis and full vitellogenesis between 17 May and 21 November. This treatment completely inhibited gametogenesis. Although vitellogenesis did not occur in the females, no major changes were observed in the ovaries, which remained at the previtellogenetic stage with apparently normal oocytes and oogonia. Drastic changes in the male testes were found, however, with disappearance of spermatogonia at the highest doses of MT and E. In sexually mature fish, MT did not appear to be a growth promoter. In both males and females, E inhibited growth and induced high mortality.