Endocrine Aspects of Salmonid Culture

SYNOPSIS Administration, by dietary supplement, of ethylestrenol to rainbow trout and to salmon parr results in significant increases in growth rate; further treatment of smolts retained in fresh water reduces the growth rate. Treated parr develop into 1 + smolts in significantly lower proportion than controls, but have a higher condition factor. Stress induces in rainbow trout long-lasting reductions in plasma thyroxine levels and increases in serum cortisol concentrations. The origin and significance of these changes is discussed. The administration of 17β-oestradiol at 20 mg/kg of food for the first 30 days of feeding causes sex-reversal of male salmonids. Treatment with 17α-methyltestosterone at 3 mg/kg food for 90 days following first-feeding causes sex-reversal of female salmonids.