Abstract
The enzymatic hydrolysis of soybeans could enhance their application as an ingredient and alternative to fishmeal in aquafeeds. Here, a 10-week feeding trial was conducted to evaluate the impacts of different dietary inclusion levels of enzymatically hydrolyzed compound soy protein (EHCS) on the growth performance and intestinal health of juvenile American eels (Anguilla rostrata). Five experimental diets were formulated with graded EHCS inclusion levels at 0% (EHCS0), 8% (EHCS8), 16% (EHCS16), 24% (EHCS24), and 32% (EHCS32). Each diet was randomly assigned to four replicate tanks. The results showed that eels fed the EHCS8 diet exhibited superior growth performance, decreased serum lipid content, and increased immunity compared to those fed the EHCS0 diet. Eels fed the EHCS8 diet also displayed improved intestinal histology, enhanced antioxidant capacity and balance of intestinal microbiota as well as an enhanced proliferation of probiotics compared to those receiving the EHCS0 diet. Compared with eels fed the EHCS0 diet, those fed the EHCS16 diet exhibited comparable growth performance and values for the aforementioned markers. The quadratic regression analysis of weight gain rate and feed efficiency against the dietary EHCS inclusion levels determined the maximum levels of dietary EHCS inclusion for American eels range from 17.59% to 17.77%.