Beneficial effects of dietary papain supplementation in juvenile sterlet (Acipenser ruthenus): Growth, intestinal topography, digestive enzymes, antioxidant response, immune response, and response to a challenge test

Abstract

Juvenile sterlet (Acipenser ruthenus) were fed commercial feed (group C) and experimental feed supplemented with papain in doses of 10 g kg−1 feed (P1) and 20 g kg−1 feed (P2) for eight weeks. Growth, digestive enzyme activity, immunity parameters, pathological changes of the liver and intestine, proximate body composition, and oxidative response were assayed. A challenge test with Yersinia ruckeri was also performed. The final body weights of groups P1 (107.07 ± 7.66 g) and P2 (111.98 ± 1.93 g) were significantly (P < 0.05) higher compared to the control group (99.73 ± 2.71 g). The height of the intestinal enterocytes was the greatest in group P2, and the highest supranuclear surface of the intestinal enterocytes was noted in groups P1 and P2. The activities of α-amylase, trypsin, lipase, and leucine aminopeptidase were significantly (P < 0.05) higher in the posterior intestine of the fish from group P2 than in the other dietary treatment groups. Ceruloplasmin, total immunoglobulin (Ig), the metabolic activity of splenic macrophages (PMA), and the potential killing activity of splenic phagocytes (PKA) were significantly higher in groups P1 and P2 compared with the control group. The proliferative activities of spleen T and B-lymphocytes were significantly (P < 0.05) higher in group P2 in comparison to the control group and group P1. Total antioxidant status (TAS), superoxide dismutase (SOD), and glutathione peroxidase (GPx) were significantly increased in groups P1 and P2 compared with the control group. The glutathione reductase (GLURED) activities decreased significantly (P < 0.05) with increasing levels of papain supplementation. Furthermore, during the challenge test, fish survival was significantly higher in groups fed feed supplemented with papain. Finally, the current study indicated that supplementing feed with doses of 10 g and/or 20 g papain kg−1 for a period of 56-days improved growth efficiency and feed utilization and also stimulated immunity in aquaculture conditions.