Dietary Supplementation With DDGS in Juvenile of Rainbow Trout (Oncorhynchus mykiss): Effects on Growth Parameters, Digestive Physiology, and Gene Expression

In this study, the effects of using the distiller’s dried grains with solubles (DDGS) instead of soybean meal on rainbow trout (Oncorhynchus mykiss) were investigated. Four different experimental diets were prepared with isonitrogenous (43%) and isolipidic (19%) values, incorporating DDGS at levels of 0%, 10%, 20%, and 30%. Fish were weighed (18.5–20.2 g) and randomly distributed in 12 tanks (140 L water) with 22 fish in each tank. The feeding trial lasted 60 days and was conducted in triplicate. The best weight gain (WG), specific growth rate (SGR), and feed conversion ratio (FCR) were observed in the DDGS20 experimental group. While viscerosomatic index (VSI) and hepatosomatic index (HSI) values were found to be the highest in the DDGS30 experimental group, the spleen-somatic index (SSI) was found to be the highest in the DDGS10 experimental group (p <0.05). It was found that the nutrient digestibility ratio values and fish meat chemical composition values of the experimental diets were similar between the groups (p >0.05). Additionally, it was analyzed that the use of DDGS protein sources in diets did not negatively affect the coloration of the experimental fish. While DDGS percentage increased in the diet, hepatocyte nucleus diameter was decreasing (p <0.05). In the distal intestine, the DDGS10 and DDGS20 groups gave results that are more likely to be digestible, which depends on villi length. The results of the DDGS30 groups had no negative effects on both liver and distal intestine. The genes interferon gamma (IFN-γ), tumor necrosis factor alpha (TNF-α), interleukin 8 (IL-8), and superoxide dismutase 2 (SOD2) exhibited higher fold changes when DDGS2 contribution was present in the liver, whereas the interleukin 1 beta (IL-1β) gene exhibited lower fold change. Furthermore, the mean fold changes increased with the proportion of the DDGS additive in the immunoglobulin M (IgM) heavy chain and immunoglobulin T (IgT) genes but decreased in the catalase (CAT) and glutathione peroxidase 1 (GPX1) genes. TNF-α and SOD2 genes showed the lowest fold changes in the head kidney in the presence of DDGS20, whereas IL-1β and GPX1 genes exhibited the highest fold changes in the presence of DDGS10. Moreover, the utilization of feed additives extracted from DDGS in feed formulations resulted in cost reductions, thereby positively influencing the production cost per kilogram of feed. Among the trials, the incorporation of DDGS20 had the most beneficial impact on the cost per kilogram of fish due to its comparatively lower cost.