Effects of varying dietary levels of digestible protein and digestible energy on growth performance in juvenile Yellowstone Cutthroat Trout (Oncorhynchus clarkia bouvieri)

Abstract

Cutthroat trout (Oncorhynchus clarkii) are widely cultured in state and federal hatcheries and private farms throughout the Western United States for stock supplementation or recreational fisheries. Cutthroat Trout culture techniques often rely on methods borrowed from the culture of closely related Rainbow Trout (Oncorhynchus mykiss). Even though commercial feeds for Rainbow Trout are commonly utilized, these formulations are unlikely to be optimal for Cutthroat Trout growth. Therefore, in an effort to determine an optimal digestible protein to digestible energy ratio for raising Cutthroat Trout more efficiently, eight diets formulated with 4 different levels of digestible protein (DP: 32.5 %, 37 %, 41.7 % and 46 %) and 2 different levels of digestible energy (DE: 4370 kcal/kg and 4770 kcal/kg) were fed to triplicate tanks of Yellowstone Cutthroat Trout and compared with a commercial Rainbow Trout diet over a 12 week study. All test diets performed better on indices of biomass accrual than the commercially available diet. Results suggest commercially available Rainbow Trout diets are less efficient formulations for Yellowstone Cutthroat Trout and new formulations should be considered. Optimizing digestibility, protein retention, minimizing lipid accrual, and maintaining high biomass gain in tanks, leads to the conclusion that a diet representing a DP:DE of 68.4 mg kcal−1 performed best. Moreover, protein retention decreased as DP:DE increased across test diets. Retention of lipids and gross energy did not appear to be significantly altered by dietary DP or DE.