Comparison of the adjuvant effect of propolis and Freund on the efficacy of Aeromonas hydrophila vaccine in common carp (Cyprinus carpio)

The success of many vaccines relies on their association with selected adjuvants in order to increase their immunogenicity and ensure long-term protection. Propolis is a natural compounds, are mostly known for their immunostimulatory  properties. In this study the adjuvant effects of propolis in combination with formalin-killed A. hydrophila vaccine in Common carp (Cyprinus carpio) were evaluated and compared with Freund’s adjuvant. Three hundred juvenile carp (weighing  50.4 ± 3.2 g) were divided randomly into four groups in triplicates. The fish were intraperitonealy injected with Aeromonas hydrophila bacterin (A.h) in combination with normal saline (Formalin Killed Bacterin, FKB group), Freound (FKB +F group), and Propolis (FKB +P group) respectively. Control group  were injected with normal saline.  Serum samples were taken from fish in each group every other weeks (days 0, 14, 28 and 42) of experiment and immunological parameters including anti A.h antibody titer, serum lysozyme and antibacterial activity, complement activity, Nitro blue tetrazolium activity and serum total protein and globulin were compared among the groups. At the end of study remind fish in each group were challenged with virulent A. hydrophila and mortality recorded for 10 days and Relative Percentage Survival (RPS) calculated and compared among the groups. Results showed that not only the antibody titer, but none specific immune responses of  propolis adjuvanted groups was significantly higher than the control group (P<0.05). Besides no significant change observed in mortality rate following the challenge in propolis adjuvanted group compare to FKB group (P>0.05). According to results and based on the effect of propolis on specific (Ab titer), none specific immune response and protection rate (RPS) of common carp against A.hydrophila vaccine, it can be concluded that although  propolis as an adjuvant can promote some immune responses of common carp, it can't affect efficacy of vaccine and Ab titer of injected antigens, so it seems more work needs to present propolis as a proper candidate for development of a natural adjuvant in fish vaccines.