Soybean meal is a widely used protein source in finfish feeds, however, high inclusion rates of soybean meal (above 20-25%) can lead to gut inflammation and reduced growth efficiency in many carnivorous species. High-protein feed products extracted from yeast fermentation of corn (HPF-YFC) are potential alternatives to soybean meal that could meet the dietary protein demands of carnivorous finfish without the drawbacks commonly associated with soybean meal. This investigation examined the culture performance, intestinal histology, and expression of gut inflammation markers in rainbow trout fed experimental diets with graded levels of soybean protein and a HPF-YFC.
Rainbow trout (48.9±1.3g) were randomly distributed to twelve 100-L tanks within a recirculating aquaculture system (9 L/min inflow in tanks) with an initial stocking density of 30 fish/tank. Fish were fed four experimental diets for 70 days on a restricted feeding regime (1-3% biomass/day), and tanks were weighed and every 14 days. The four experimental diets were formulated to contain 40% protein and 20% lipids. The diets had 0% (Control), 25%, 50%, or 100% replacement of soybean meal with HPF-YFC
The mean weight, specific growth rate, and feed conversion ratio of fish were not significantly different (α=0.05) between diet groups after 69 days of feeding (139.6±7.5g final weight). Histological analysis of distal intestines showed a significant increase in villi length (p=0.012) and villi length:width ratio (p=0.005) associated with the 100% HPF-YFC diet group (Figure). The expression of gut inflammation markers TNF-α, IL10, and MMP9 tended to be lower in the 50% and 100% HPF-YFC diet groups, relative to the soybean control group, although these differences were not statistically significant. These results suggest that the replacement of soybean protein with HPF-YFC protein in rainbow trout diets does not impair growth performance and improves gut health.