Modulation of systemic and mucosal immune responses of Catla catla (Hamilton, 1822) experimentally challenged with gill monogeneans.

The present study investigated the modulation of systemic and mucosal immunity of catla (Catla catla) experimentally challenged with gill monogeneans. Fingerlings of catla (24.2 ± 1.5 g) without any parasites were randomly distributed into two groups each comprising quadruplicate tanks (10 fish per tank). The fish in the infected group were challenged with gill monogeneans by cohabitation method. The control group fish were not exposed to parasites. Serum and mucus were collected from both control and infected fish and different immunological parameters were measured at weekly interval for four weeks. Monogeneans on the fish gills were also quantified from infected fish at weekly interval. Different systemic immunological parameters viz. myeloperoxidase content, alkaline phosphatase and hemolytic activity of serum showed a significant increase (p < .05) in infected group. However, respiratory burst activity, total serum protein and anti-protease activity did not show any significant enhancement (p < .05) in infected group compared to control. In case of mucosal parameters, myeloperoxidase content, alkaline phosphatase activity, total protein content and anti-protease activity of mucus showed significant enhancement (p < .05) in infected group compared to control. Parasite prevalence was 100% in the infected group in all the sampling weeks. The mean intensity of parasites was progressively increased and the highest number of monogeneans per gill (45 ± 4.56) was observed during 4th week post challenge. Control group had mean intensity and prevalence of zero. In conclusion, there was the participation of immune system components against monogenean infection in catla. However, the progressive increase in monogenean intensity indicates some immune evasion mechanism available with the monogenean to co-exist with the host in the face of host's immune responses.