Effects of Substituting Fishmeal with Soy Protein Concentrate Supplemented with Essential Amino Acids in the Olive Flounder (Paralichthys olivaceus) Diet on the Expression of Genes Related to Growth, Stress, Immunity, and Digestive Enzyme.

Simple Summary: This experiment was conducted in accordance with the prevailing trend of identifying alternative sources of nutrition to compensate for the economic shortcomings of fish meal in the aquaculture industry. The experiment employed soybean-based concentrated protein, which is approximately half the cost of fish meal, and focused on investigating its impact on growth and physiological processes. Three experimental diets were prepared: the control diet (Con) contained 60% FM, and the experimental diets contained 25% (SPC25) and 50% (SPC50) FM replaced by SPC. Following the 140-day feeding period, no significant differences in growth performance were observed. However, an increase in the replacement rate was associated with a reduction in stress and immune sensitivity, while the SPC25 treatment exhibited elevated levels of digestive enzyme-related genes. Therefore, substituting 25% FM with SPC was most effective for commercial fish farming. This study identified the effects of substituting fishmeal (FM) with soy protein concentrate (SPC) supplemented with lysine and methionine in the olive flounder (Paralichthys olivaceus) diet on the expression of genes related to growth, stress, immunity, and digestion. Three experimental diets were prepared; the control diet (Con) contained 60% FM, and the experimental diets contained 25% (SPC25) and 50% (SPC50) FM replaced by SPC. After the 140-day feeding period, weight gain, specific growth rate, feed availability, biological indices, and chemical composition of the muscle were not significantly affected by the dietary treatments. The gene expression levels of growth-related genes (IGF, GFB-3), immune-related genes (IL-8 and caspase), and stress-related genes (SOD, GPX, PRX, TRX) were higher in Con fish than in those fed the SPC25 and SPC50 diets. Chymo-TRY2, TRY2, and TRY3 in the stomach of fish fed the SPC25 diet were higher than fish fed the Con or SPC50 diets. TRY2 and lipase of fish fed the SPC25 diet were higher than those of fish fed the other diets but TRY3 was not significantly affected by the treatments in the intestine. In conclusion, substituting 25% FM with SPC was the most effective diet for the expression of growth, immune, stress, and digestive enzyme genes. [ABSTRACT FROM AUTHOR]