Photoperiodic alteration modulates immune responses of freshwater snakehead teleost, Channa punctatus.

In fish, photoperiod has a significant influence on health by modulating physiological processes, including reproduction, growth, and stress response. However, its impact on the immune system is still unexplored. This study aimed to find the effect of different photoperiodic regimes on immune responses in Channa punctatus. Innate immune functions were evaluated by analyzing superoxide anion production, phagocytosis, and nitrite production in head kidney and spleen cells. Cell-mediated immune function was assessed by lymphocyte proliferation assay. The findings demonstrated that splenic phagocyte activity increased in fish kept in 8L:16D photoperiod, while respiratory burst activity decreased. Nitrite production was significantly reduced in the animals kept in either long (16L:8D) or short (8L:16D) photoperiods when compared with 12L:12D animals. Further, mitogen-induced splenic and head kidney lymphocyte proliferations were enhanced in both long and short photoperiods. The results indicate that the head kidney and spleen cells respond differently to photoperiodic modulation, reflecting the distinct immunological roles of these organs. The altered photoperiod may play a crucial role in the modulating immune functioning, which may be of adaptive significance in fluctuating environmental conditions.