Evaluation of Two Higher-Fat Diets and a Lower-Fat Diet for Rainbow Trout

Abstract

Rainbow trout, Oncorhynchus mykiss, were raised for 12 weeks at 13°C in flow-through outdoor tanks with ad libitum feeding by means of demand feeders. Diets tested were Zeigler Hi-Fat Trout Grower (ZTG; minimum 38% protein, 12% fat), Zeigler Experimental Diet 45/17 (ZED; minimum 45% protein, 17% fat), and EWOS Vextra Chinook EST 72 Extruded Feed (EVC; minimum 45% protein, 18% fat). Fish fed EVC and ZED performed similarly in many respects. such as length gain, length growth rate, and food conversion, but those fed EVC had significantly greater weight gain and lower phosphorus losses per unit feed and per unit weight gain. Fish fed ZTG had less whole-body fat than other diets but were significantly inferior to one or both other diets in weight gain (<EVC), food conversion (>both), and phosphorus loss per unit weight gain (>EVC). Better feed conversion and growth from higher-fat diets may make them preferable to lower-fat ones for rainbow trout.