Feed characteristics alter growth efficiency of cutthroat trout

Authors: HAM, B - Us Fish And Wildlife Service; SEALEY, W - Us Fish And Wildlife Service; MYRICK, C - Colorado State University; Barrows, Frederic; DUFF, G - Montana State University; YEOMAN, C - Montana State University; MASKILL, M - Us Fish And Wildlife Service

Submitted to: Journal of Fish and Wildlife Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/21/2014
Publication Date: 6/20/2015
Citation: Ham, B.R., Sealey, W.M., Myrick, C.A., Barrows, F., Duff, G.C., Yeoman, C.J., Maskill, M.G. 2015. Feed characteristics alter growth efficiency of cutthroat trout. Journal of Fish and Wildlife Management. 6(1):83-91.

Interpretive Summary: Cutthroat trout is a native species in many western states of the U.S., and is relatively undomesticated compared to rainbow trout. There is increasing interest in raising cutthroat trout both for pond stocking and food fish production. Due to the volatile feed ingredient prices current commercial trout diets contain higher levels of plant proteins than in the past. A feeding study was conducted to determine if cutthroat trout can tolerate higher levels of soybean products. Soybean meal and soy protein concentrate were both fed at levels increasing from 0 to 30% of the diet. The trout grew well with the higher soy inclusion levels, but inflammation in the intestine was observed in the fish fed the highest level of soy. Cutthroat trout do not appear to be significantly different from rainbow trout in sensitivity to dietary soy.

Technical Abstract: The shift in commercial Rainbow Trout Oncorhynchus mykiss diet formulations toward formulations with more plant ingredient inclusion, and specifically increased soy product inclusion, may have negative implications for less domesticated trout species fed these modern diets. Therefore, the objective of this study was to examine the effects of increasing dietary soybean meal and soy protein concentrate inclusion on growth efficiency and intestinal health of Cutthroat Trout. To achieve this objective, a feeding trial was conducted with juvenile Snake River Cutthroat Trout (Oncorhynchus clarkia behnkei) fed a practical type formulation with 0, 5, 10, 15 or 30% dietary soybean meal or soy protein concentrate. Feed and consumption, weight gain, proximate composition, intestinal health and survival were compared. Juvenile Snake River Cutthroat Trout (initial weight 28.1g/fish ± standard deviation of 1.0g) were stocked at 20 fish/tank in 200 L tanks with three replicate tanks per diet. Fish were fed their respective diets for 10 weeks. Final fish weight was affected by dietary soy inclusion level (P=0.0001) but not type (P=0.7790) and no interaction was observed (P=0.6019). Snake River Cutthroat Trout fed the diets with the highest level of soy protein inclusion (30%) were significantly larger than fish fed all other diets, with a final average fish weight of greater than 130 g (P=0.0001). Feed conversion ratios were higher in fish fed diets with 0 and 5% soy inclusion than fish fed the 10 or 30% inclusion diets (P=0.0044). No significant effect of soy inclusion level (P=0.0825) on feed intake was observed. Increased inflammation and decreased vacuolization, however, was observed in the intestine of Cutthroat Trout fed the 30% soybean meal and soy protein concentrate diets. Additional research is necessary to determine whether the intestinal pathology observed can predispose cutthroat trout to pathogenic disease and/or negatively affect growth with extended feeding.