Immunomodulatory effects of dietary intake of chitin, chitosan and levamisole on the immune system of rainbow trout (Oncorhynchus mykiss) and control of Aeromonas hydrophila infection in ponds

Objective: Aeromonas hydrophila is associated with disease in important cultural fish and produces stress related diseases with the common bacterial symptoms. Immunostimulation is one of the useful tools in aquaculture where vaccination or treatment by injections are difficult and laborious processes, and where repeated chemotherapy poses a problem of developing drug resistant strains of pathogens. Immunostimulants such as levamisole, chitin, chitosan, and other combinations, have the ability to increase resistance to bacterial infections. The present study was undertaken to evaluate the comparative efficacy of chitin, chitosan and levamisole on enhancing nonspecific immunity in challenged with A. hydrophila. Method & Materials: A. hydrophila (RI), were routinely grown in TSA at 22Cº. Immature O. mykiss, were kept in 200 l tanks with optimal condition. Chitin, chitosan and levamisole (1 g/kg), were incorporated with commercial trout pellets. Each of treatment fish, except for control group, were fed (3% BW), with pellets contains chitin, chitosan and levamisole for 45 days. After 45th day, 40 fish of each group were challenged with 1.5±0.3×106 cfuml-1 of A. hydrophila and reared in separate tank. Relative percentage survival, WBC and lysozyme activity was recorded after 15 days challenge. Results & Conclusion: The results of the present study clearly show that oral administration of the chitosan, levamisole and chitin results in enhancement of leucocyte function and 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 and white blood cell count were studied to assess the immune response of rainbow trout. 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 (84%) followed by levamisole (62%), and chitin (38%). The results indicated that dietary intake of chitosan enhances the innate immune system and survivability of rainbow trout (O. mykiss) in tanks. The role of chitosan, chitin and levamisole as immunostimulants with regard to protection against A. hydrophila infection is discussed. In conclusion, the present study has shown that these immunostimulants in the diet increased the non-specific immunity and significantly decreased mortality when O. mykiss were experimentally infected with A. hydrophila, a bacterial pathogen.

کلیدواژه ها:

Aeromonas hydrophila ، Immunostimulant ، Survival ، Hematology ، growth