The effects of long-term estradiol-17beta treatment on the growth and physiology of female triploid brook trout (Salvelinus fontinalis).

Triploid female fish show impaired gonadal development, which results in the production of only a few oocytes relative to diploids. The rate of maturation of these few oocytes in much slower relative to those of diploids and is attributed to an insufficient estradiol-17beta (E(2)) stimulus. Female triploid brook trout, aged 2+, were fed E(2) for seven months (i.e., July 1998 to February 1999) in an attempt to increase plasma E(2) comparable to diploid levels and thereby accelerate rates of oocyte growth. Compared to triploids fed a normal diet (i.e., control-triploids), the administration of 30 mg E(2)/kg feed to triploids (i.e., E(2)-treated-triploids) led to the development of secondary sex characteristics, a significant reduction in hematocrit and total blood hemoglobin level, a decrease in plasma testosterone and no weight gain. Plasma vitellogenin was significantly higher in E(2)-treated-triploids than in control-triploids and diploids at every month except October 1999. Although greater than in the control-triploids, plasma E(2) for the E(2)-treated-triploids did not attain the high levels shown by the diploids during the months of peak vitellogenesis (i.e., September and October). Following maturation and spawning of diploids, sacrificed E(2)-treated and control-triploids showed no differences in ovarian development or liver size. The E(2) dose for the treated-triploids was increased to 80 mg E(2)/kg feed for approximately seven more weeks in a further attempt to increase plasma E(2), with no success. It is suggested that the low plasma E(2) of the treated-triploids was the result of a high metabolic clearance rate. Copyright 2003 Elsevier Science (USA)