Evaluation of dietary soy sensitivity in snake river cutthroat trout

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

Submitted to: North American Journal of Aquaculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/21/2014
Publication Date: 3/20/2015
Citation: Ham, B.R., Myrick, C.A., Barrows, F., Yeoman, C.J., Duff, G.C., Maskill, M.G., Sealey, W.M. 2015. Evaluation of dietary soy sensitivity in snake river cutthroat trout. North American Journal of Aquaculture. 77(2):195-205.

Interpretive Summary: In an effort to improve the growth rate and survival of farmed cutthroat trout a feeding study was conducted using feed with different physical characteristics. Most commercial trout feeds are very hard and float. This type of feed was along with a sinking feed a semi-moist soft texture feed and a flake feed as is used in aquariums. Result of the study showed similar results for two strains of cutthroat trout. The only difference detected was for the fish fed the flake feed and that they grew slower. This study demonstrates that for juvenile cutthroat trout flake feeds are not adequate.

Technical Abstract: Hatchery-cultured cutthroat trout fed some commercially available rainbow trout feeds display slow growth and increased mortality. Feed characteristics such as buoyancy and texture alter feed acceptance in some fish species but their effects have not been adequately addressed in cutthroat trout. Therefore, the objective of this study was to examine whether feed structure and behavior preferences explain the decreased hatchery performance of juvenile cutthroat trout. To achieve this, we conducted two feeding trials in which Westslope cutthroat trout Oncorhynchus clarkii lewisi and Snake River finespotted cutthroat trout O. clarkii behnkei were fed a single diet formulation manufactured to display four different characteristics (floating, sinking, semi-moist pellets, or a flake feed) and compared consumption, weight gain and survival. In the first feeding trial, Westslope cutthroat trout (initial weight 11.3 g ± 0.5 g) were stocked at 20 fish per tank. Two different sizes of tanks were used, with four replicate small tanks (54-L) and two replicate large tanks (96-L) per feed type. Results of the first trial demonstrated a significant effect of feed type but not tank size on weight gain of Westslope cutthroat trout with no interaction. Westslope cutthroat trout fed the flake feed gained less weight than fish fed any of the other feed types. Feed conversion ratio (FCR) was affected by both feed type and tank size with no interaction. In a second feeding trial, Snake River cutthroat trout (initial weight 19.5 ± 0.5 g) were stocked at 20 fish/tank in 96-L tanks with four replicate tanks per feed type. Results of the second trial demonstrated that Snake River cutthroat trout fed the flake feed grew less, had higher FCR, elevated hepatosomatic index and reduced muscle ratio compared to fish fed the other feeds. Results demonstrate that flake feeds are not adequate for cutthroat trout at this life stage. However, additional research is needed to address other culture-related limitations since only minor differences between fish fed other feed types were detected.