Partial and total replacement of soybean meal with a corn‐fermented protein product in Rainbow Trout feeds.

Objective: Corn‐fermented protein products (CFP) from the bioethanol industry have strong potential as alternatives to traditional plant protein sources in finfish diets. This study examined the culture performance, apparent digestibility, intestinal histology, and expression of gut inflammation markers in juvenile Rainbow Trout Oncorhynchus mykiss fed experimental diets with graded levels of soybean meal and CFP. Methods: Four experimental diets were formulated to contain 40% protein and 20% lipids, and the diets incrementally replaced soybean meal with CFP (0% [Control], 25%, 50%, or 100% replacement). Juvenile Rainbow Trout (48.9 ± 1.3 g) were randomly distributed to 12 100‐L tanks within a recirculating aquaculture system (30 fish/tank). Fish were fed one of the four experimental diets on a restricted feeding regime (1–3% biomass/day), and tanks were weighed every 14 days for 70 days. Result: The mean weight, specific growth rate, feed conversion ratio, survival, and proximate composition of fish were not significantly different (α = 0.05) between the diet groups after 70 days of feeding (139.6 ± 7.5 g final weight). Apparent protein digestibility was significantly higher in the 50% CFP diet group than the Control group (80.3 ± 1.2% and 77.6 ± 1.2%, respectively). Histological analysis of distal intestines showed significantly larger villi lengths and villi length‐to‐width ratios in fish fed the 100% CFP diet, relative to fish fed the Control and 25% CFP diets. The expression of gut inflammation markers tumor necrosis factor alpha (TNF‐α), interleukin (IL)10, and matrix metalloproteinase‐9 (MMP9) trended lower in the 50% and 100% CFP diet groups compared to the Control group. The expression of the nutrient absorption markers PepT1 and FABP2 trended higher in the 50% and 100% CFP diet groups relative to the Control group. Conclusion: The results of this study suggested that the replacement of soybean meal with CFP in Rainbow Trout grow‐out diets did not impair growth performance and improved overall protein digestibility and gut health. Impact statementThis study evaluated the use of a value‐added corn ethanol by‐product as a protein and fat source in Rainbow Trout feeds. This new ingredient could be more affordable than traditional plant protein and fat sources in trout feeds and would not divert a potential human food crop (soybean) towards animal feeds. The study found that replacing soybean‐based protein and fat sources in trout feeds with the value‐added corn ethanol by‐product did not affect fish growth rates but did improve gut health and protein digestibility. These results support the use of this new ingredient in trout feeds and the study offers a good launch point for future research on the topic. [ABSTRACT FROM AUTHOR]