Seasonal immune rhythm of leukocytes in the freshwater snakehead fish, Channa punctatus.

Annual rhythms are observed in many physiological processes and are an important approach to cope with seasonal stressors. The use of lower vertebrates as an experimental model is crucial to understand the evolution of this biological clock. This study aims to characterize the seasonal variability in the leukocyte immune responses in Channa punctatus. Leukocytes were harvested from peripheral blood and respiratory burst activity, leukocyte phagocytosis, and nitrite production were assessed to study innate immunity. Peripheral blood lymphocytes were segregated by centrifugation (density gradient) and proliferative responses of lymphocytes, in the presence of mitogens, were used to study cell-mediated immunity. Annual rhythms were validated in superoxide anion production, nitrite release and phagocytosis. Cosinor analysis revealed a differential pattern of lymphocyte proliferation which was dependent upon season and mitogen used. It was concluded that seasonal variation in immune activity might be associated with annual adaptation against diseases and the optimum immune status of seasonal breeders like fish helps them fight seasonal changes.