Juvenile sterlet (Acipenser ruthenus) were fed commercial feed (group C) and experimental feed supplemented with papain in doses 10 g kg-1 (P1) and 20 g kg-1 (P2) feed for 8 weeks. Growth, digestive enzyme activity, immunity parameters, pathological changes of the liver and intestine, chemical body composition and oxidative response were assayed. Challenge test using Yersinia ruckeri was also performed. Final body weight of groups P1 (107.07 ± 7.66 g) and P2 (111.98 ± 1.93 g) was significantly (P < 0.05) higher compared to control group (99.73 ± 2.71 g). The highest intestinal enterocytes was detected in group P2, and the highest supranuclear surface of the intestinal enterocytes was found in groups P1 and P2. The activities of α-amylase, trypsin, lipase and leucine aminopeptidase were significantly (P < 0.05) higher in posterior intestine of fish fed group (P2) than other treatment groups. Ceruloplasmin, total Immunoglobulin (Ig), metabolic activity of splenic macrophages (PMA) and potential killing activity of splenic phagocytes (PKA) were significantly higher in groups P1 and P2 compared with control group. While, the proliferative activity of spleen T and B-lymphocytes were significantly (P < 0.05) higher in group P2 in comparison to the control and group P1. Total antioxidant status (TAS), superoxide dismutase (SOD) and glutathione peroxidase (GPx) were significantly increased in groups P1 and P2 compared with control group. The activities of glutathione reductase was significantly (P < 0.05) decreased with increasing levels of papain supplementation. Furthermore, during challenge test, survival of fish was significantly higher in groups 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-day improved growth efficiency and feed utilization, and also stimulated immunity in aquaculture conditions. |
