RESUMO
The unusual presence of vitellogenin in the plasma of male and nonvitellogenic female Siberian sturgeon has been demonstrated previously (Pelissero and Le Menn, 1988; Pelissero et al., 1989a) and was attributed to dietary effects. The present study examines estrogenic effects of dietary soya bean meal and of commercial trout diet on vitellogenesis in sturgeon. The 4-month study compared three diets, one commercial (T) and two experimental synthetic diets, one containing casein alone (SC for synthetic diet made on casein), and the other casein and soya bean (SS for synthetic diet made with soya bean) as protein sources. The dietary soya bean meal contained plant isoflavonic compounds which are well known to mimic the effects of estrogens in mammals. The SC diet, free of estrogenic compounds, served as the reference diet. When fed with the SC diet, sturgeons showed significantly lower plasma vitellogenin levels (0.0045 +/- 0.0012 mg/ml) compared with those fed the commercial diet (1.24 +/- 0.37 mg/ml). The SS diet had a very pronounced effect on the plasma vitellogenin level, which at the end of the experiment had reached 6 mg vitellogenin/ml. In no case was estradiol detectable in the plasma. Plasma androgen levels were high in all the three groups throughout the study period, and not significantly different from one another. Sturgeon fed the T diet had larger livers, with enlarged hepatocytes, compared with those fed the SS and SC diets.
