Dietary Androgen-Estrogen Combinations in Growth Promotion in Fingerling Rainbow Trout

Abstract

Eight semipurified diets containing various combinations (totaling 2.0 mg/kg diet) of the androgens 17α-methyltestosterone (MT) and 5α-dihydrotestosterone (DHT) and the estrogen estradiol-17β (ES) were fed to four replicate groups of rainbow trout (Salmo gairdneri) fingerlings (initial weight = 0.7 g) for 10 weeks to determine relative growth-promoting effectiveness. Fish fed MT alone or in combination with DHT gained 27.3% more body weight than controls (P < 0.05). Estradiol alone or in combination with DHT decreased body weight gain (P < 0.05) and inclusion of the estrogen in diets containing MT suppressed (P < 0.05) the anabolic effectiveness of this androgen. Dihydrotestosterone had no effect (P > 0.20) on body weight. Feed conversion (weight of feed fed/fish weight gained) and average weight gain were recorded over bimonthly periods to examine the effects of treatments on these characteristics. Methyltestosterone enhanced growth (P < 0.05) without changing feed utilization. Decreases (P < 0.01) in average weight gain were associated with increases (P < 0.05) in feed conversion of fish fed ES-treated diets, suggesting a negative effect of estrogen treatment on feed utilization or appetite at the levels used.