BACKGROUND: Recently chitosan nanoparticles have been applied as an immunostimulant and adjuvant in biomedical fields. OBJECTIVES: In this study the adjuvant effects of nanochitosan, derived from shrimp shell's chithin, on immunogenicity of Aeromonas hydrophila vaccine in common carp were evaluated. METHODS: Totally 300 juvenile common carp (51±5.6 g, Mean ±SD) were randomly divided into four groups each contained three subgroups with 25 fishes. Groups 1, 2 and 3 were immunized intraperitoneally with A. hydrophila vaccine. No adjuvant used in group 1, but nanochitosan and freund adjuvant were used with vaccine in groups 2 and 3 respectively. Group 4 (Control) injected with normal saline instead of vaccine. Fish were immunised at days zero and 14 and fishes were reared in the same situation for 6 weeks. Serum samples were taken every other weeks and immunological parameters including WBC, serum lysozyme and bactericidal activity, serum complement activity, NBT reduction activity, total protein and globulin levels and anti A.hydrophila antibody titer were compared among the groups. At the end of experiment all groups were challenged with LD50 concentration of A. hydrophila and mortality recorded for ten days. RESULTS: WBC, serum lysozyme and complement activity, NBT activity, globulin level and anti A.hydrophila antibody titer were increased in nanochitosan and freund groups compare to control group (P<0.05). Serum bactericidal activity and serum albumin level showed no significant change among the groups (P>0.05). Challenge mortality decreased in immunised groups compare to control. CONCLUSIONS: Nonochitosan posses proper adjuvant effects which is comparable with freund adjuvant and can be a good candidate as an alternative to current adjuvant in fish vaccines.

Introduction: Immune-potentiating functions of Lactobacillus plantarum strains in the common carp were evaluated. Material and Methods: Fourteen days of feeding fish dry diet supplemented with the bacteria provided parameters of nonspecific humoral immunity (lysozyme, ceruloplasmin, γ-globulin, total protein levels, and serum bactericidal activity) and cellular immunity (pinocytosis, respiratory burst activity, and potential killing activity of organ phagocytes), as well as the proliferative response of organ lymphocytes stimulated with mitogens. The resistance of fish to infection with Aeromonas hydrophila was also determined. Results: Dietary supplementation with L. plantarum had a substantial influence on the activity of organ phagocytes, especially the potential killing activity of head kidney cells. A significant increase in the proliferative activity of LPS-stimulated B lymphocytes and in the levels of γ-globulins and total protein was observed. The supplemented diet conveyed higher resistance than the control diet as the cumulative fish mortalities after infection with A. hydrophila were 65% and 85%, respectively. Conclusion: The results indicate that dietary supplementation with L. plantarum stimulates the antibacterial resistance of common carp and may reinforce defence against bacterial infections, but further studies need to be conducted.