Changes in Dietary Protein to Metabolizable Energy Needs of 17α-Methyltestosterone Treated Juvenile Rainbow Trout1,2

Two consecutive feeding trials were used to examine optimum dietary protein to metabolizable energy (P:ME) and ME needs of juvenile rainbow trout fed semipurified diets supplemented with 2.0 mg 17^α-methyltestosterone (MT)/kg of dry ingredients. In trial 1, five diets containing 80,100, 120, 140, and 160 mg protein/kcal ME of dry diet at a constant 390 kcal ME/100 g of dry diet were used. In trial 2, four diets were prepared with 300, 340, 370, and 390 kcal dietary ME at a P:ME ratio of 100. Diets were prepared with and without MT and fed for 8 weeks to 5.4 g initial weight fish in trial 1 and 3.7 g initial weight fish in trial 2. Proximate composition of the whole body (WB) and empty carcass (EC = an eviscerated whole body) of fish was measured at the end of both trials. In trial 1, maximum efficient protein gain (MEPG) values of MT treated fish were correspondingly higher than the values obtained for controls at all dietary P:ME ratios fed except for those fish fed at a P:ME ratio of 80. The optimum P:ME ratio for MT treated fish was 100 and for control fish was 120. In trial 2, all MT treated fish fed diets containing 340 kcal ME/100 g and above had a higher MEPG value than all control fish. The diet containing an ME level of 340 kcal was considered optimum for growth of MT treated fish fed a dietary P:ME ratio of 100. MT treatment increased EC, but did not change WB fat content of fish in both trials.