The comparative effectiveness of the natural and a synthetic estrogen for the direct feminization of chinook salmon (Oncorhynchus tshawytscha)

11 pages, 4 figures

The natural estrogen estradiol-17β (E2) and the synthetic estrogen ethynylestradiol-17α (EE2) were administered in single-immersion treatments of 400 μg/1 for 1, 2, 4 or 8 h to groups of newly-hatched chinook salmon. The effects of these treatments on gonadal development were evaluated by histological analysis. One-hundred percent females were obtained with a 2-h treatment with EE2. However, higher doses progressively reduced the number of females to 83%. Estradiol-17β (E2) showed a clear treatment duration/response relationship, and 100% females were obtained with an 8-h immersion. Of the females in the EE2-treated groups 20.8 to 40% and 11.1 to 34.7% in the E2-treated groups had affected ovaries, which were characterized as having a reduced number of oocytes, a reduced crosssectional area and by the presence of the vascular system typical of males. Side effects included a slight decrease in survival to 86.8% (E2-treated groups) or 82.6% (EE2-treated groups), compared to a control value of 99%. Treatments also resulted in a slight increase of both weight and length. This increase was related to the hormone administered (EE2 > E2), but not to the duration of the immersion. Since monosex milt is only available at present for a limited number of genetic stocks of some commercially-important species, the present method, due to its simplicity and benefits, offers an alternative approach to the direct feminization of salmonids

FP was supported by a Scholarship from the Government of Valencia (Spain)

Peer reviewed