Immunomodulatory effects of dietary intake of chitin, chitosan and levamisole on the immune system of Cyprinus carpio and control of Aeromonas hydrophila infection in ponds

To determine the effect of chitin, chitosan and levamisole on the immune response and growth of common carp ( Cyprinus carpio) under field conditions, fish were fed with these compounds for a period of 90 days and then challenged with Aeromonas hydrophila. Dietary supplementation of chitosan, levamisole and chitin enhanced the growth of all treated fish significantly ( P < 0.05) compared to fish fed with non-supplemented diet. The highest growth was recorded in the chitosan fed fish (94.92 ± 9.36 g) followed by levamisole (93.25 ± 8.4 g) and chitin (63.54 ± 4.7 g). Lysozyme, white blood cell count (WBC) and NBT assay were studied to assess the immune response of carps. Dietary supplementation of chitin, chitosan and levamisole significantly stimulated the lysozyme activity ( P < 0.001), and NBT reduction ( P < 0.001). When the treated fish were challenged with A. hydrophila on the 45th day, the relative percentage survival (RPS) was significantly higher in chitosan fed fishes (80%) followed by levamisole (66.7%), and chitin (40%). However, the RPS decreased to 68.9%, 57.8% and 37.5% on the 90th day after the challenge with A. hydrophila. The results indicate that dietary intake of chitosan enhances the innate immune system and survivability of common carp ( C. carpio) in ponds. The role of chitosan, chitin and levamisole as immunostimulants with regard to protection against A. hydrophila infection is discussed.