Effects Of Chitosan On Non-specific Immunity And Growth Of Yellow Catfish

Changes of the peritoneal exudate leukocytes (PEL) of the yellow catfish (Pelteobagrus fulvidraco) after chitosan injection were studied. Chitosan was injected intraperitoneally at the dose of 2 mg per fish, and the PEL were collected at 2, 4, 6 or 10 d after injection. Then the microstructure and ultrastructure, differential leukocyte counting and phagocytosis of PEL were investigated. The results showed that: (1)the PEL included neutrophils, macrophages and lymphocytes. Numerous vacuoles in macrophages were appeared after chitosan injection; (2)the percentage of neutrophils were increased continuously and the percentage of macrophages were decreased continuously. But there were no changes in the percentage of the lymphocytes; (3)the phagocytic activity in the PEL were increased significantly.Method of incorporation of chitosan in the diet was used to study effects of chitosan on the non-specific immunity and growth of yellow catfish. Chitosan was incorporated into diet in a concentration of 0 g/kg, 5 g/kg, 10 g/kg, 20 g/kg. The chitosan containing diet was administrated at 3% of body weight per day for 60 days. Fish of each group were randomly sampled at 10, 20, 30 or 60 d. The lysozyme activity, contents of complement 3 and 4 (C3 and C4), phagocytic activity, leukocyte number, activity of head kidney phagocytes were examined. The immunoprotection rate and the specific growth rate (SGR) were performed at 60 d. The results showed that: (l)no significant changes in the peripheral leukocyte number by long-term oral administration of chitosan. But the percentage of lymphocyte in differential leukocyte counting from 20 d were significantly increased (P<0.05); (2) the chitosan could significantly increase the phagocytic activity of the peripheral leukocyte. Compared with the control groups, the phagocytic activity in the 10 g/kg and 20 g/kg groups were increased significantly (P<0.05) from 10 d, but in 20 g/kg group the increase at 60 d disappeared; (3) the serum lysozyme activity was increased significantly (p<0.05) at 10, 20, 30 d, but the increase at 60 d disappeared; (4) C3 and C4 contents in serum were increased significantly from 10 d, but the significant difference in 5g/kg and 10g/kg group at 60 d and in 20g/kg group at 30 d vanished; (5)chitosan improved the phagocytic and bactericidal abilities of the head kidney phagocytes, while had no influence on the chemotaxis of the phagocytes. The most effective concentration of administration of chitosan was 5-10g/kg; (6)the immunoprotection rate in 5 g/kg group was (88.45±2.16)%, (82.24±2.31) % in 10 g/kg group and (70.19±1.21) % in 20 g/kg; (7) the SGR in 5g/kg or 10g/kg groups increased significantly, but no changes in 20g/kg group. It can be concluded that the chitosan incorporated in a concentration of 5 g/kg and 10 g/kg in diet can significantly improved the non-specific immunity and growth of yellow catfish.