ABSTRACT
Estuaries are considered as highly potential area for that including feeding, spawning and nursery rearing of most of the finfishes and shellfishes. In the present investigation, two species of catfish (M.gulio and M.vittatus) were selected to study the impact of season on their immune organs (kidney and spleen) and selected immune response from Vellar estuary. The physico-chemical parameters (pH, temperature, salinity and rainfall) were measured during the sampling period 2009-10. The non-specific immune parameters (WBC count, lysozyme activity and NBT assay) were analyzed. The immune organs (head-kidney and spleen) variation was also observed by histological studies. Our results stated that the WBCs count of M. gulio and M. vittatus increased during summer (10.3 and 10.1 X 106 ml-1) season and decreased in monsoon (6.8 and 7.0 X 106 ml-1). In contrast, lysozyme activity was highest in post monsoon (1540 and 1525 U min-1 ml-1) and lowest in summer (1000 and 960 U min-1 ml-1). The activity of NBT was highest in monsoon (0.68 and 0.65 at 540 nm) and lowest in summer (0.012 and 0.2 at 540 nm). The histological observation implies that the cell variations were different in respect to different seasons.