Evaluation of Dietary Soy Sensitivity in Snake River Cutthroat Trout

Abstract

The shift in commercial diet formulations for Rainbow Trout Oncorhynchus mykiss toward formulations that include more plant ingredients, specifically an increased inclusion of soy products, 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 O. clarkii. To achieve this objective, a feeding trial was conducted with juvenile Snake River Cutthroat Trout O. clarkii behnkei fed a practical type formulation that included 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, 28.1 ± 1.0 g/fish [mean ± SD]) were stocked at 20 fish per 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 and had 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 in fish fed the 10% or 30% soy 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 histological samples of 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.

Prebiotic Supplementation has Only Minimal Effects on Growth Efficiency, Intestinal Health and Disease Resistance of Westslope Cutthroat Trout Oncorhynchus clarkii lewisi Fed 30% Soybean Meal

“…The lack of effect of soybean meal on growth of cutthroat trout recapitulates the results of our previous study in cutthroat trout ( 38 ). It is generally accepted that low to moderate levels of soybean meal may be included in salmonid diets without serious negative effects on growth or feed utilization ( 60 , 61 ) as long as diets are formulated to meet the fish’s nutritional needs, but inflammatory responses of the gut still will be present ( 62 ).…”

“…It is generally accepted that low to moderate levels of soybean meal may be included in salmonid diets without serious negative effects on growth or feed utilization ( 60 , 61 ) as long as diets are formulated to meet the fish’s nutritional needs, but inflammatory responses of the gut still will be present ( 62 ). The soybean levels investigated in the current study demonstrated soybean meal-level-dependent negative effects on gut health similar to that previously observed for juvenile rainbow trout ( 39 , 40 ) and more recently in cutthroat trout in our laboratory ( 38 ). Iwashita et al ( 63 ) attributed similar effects on gut histology to soybean lectins and saponins when these anti-nutrients were included at a level equivalent to 50% SBM inclusion even though growth rate was not impaired.…”

“…Previous research in our laboratory demonstrated that normal growth rates in Snake River cutthroat trout ( Oncorhynchus clarkia behnkei ) fed 30% soybean meal in a 10-week feeding trial ( 38 ). However, the histopathology data in that study demonstrated soy-level-dependent negative effects on gut health similar to that previously observed for juvenile trout ( 39 , 40 ).…”