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

Abstract

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-17β (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.