Variations in immunological stress responses in Heteropneustes fossilis to short term and long term hypoxia

The effects of stress on organisms are wide ranging and so are the responses. In this study, exposures to different durations and intensity of hypoxia stress and their effects were considered. The present investigation focusses on the effects of short (<3h) and long term (8-12h) exposure to moderate (30-50% O2 saturation) as well as acute (<30% O2 saturation) hypoxia conditions on the haematological and immunological parameters in an airbreathing fish, Heteropneustes fossilis (Bloch, 1872). A significant increase (p<0.05) in erythrocyte numbers was observed during exposure to both short and long term moderate hypoxia whereas WBC counts and haematocrit values showed significant (p<0.05) increase during exposure to short term acute hypoxia. The immunological parameters showed a significant decrease (p<0.05) in total WBC counts, lymhopenia during short term exposure to moderate hypoxia and significant increase in total WBC count and neutrophilia, upon exposure to short term acute hypoxia. N/L (neutrophil/lymphocyte ratio) ratio – an important stress biomarker, was found to be increased significantly in the fishes exposed to short term acute hypoxia condition. H. fossilis, an airbreathing fish is adapted to living in low oxygen environments. An immunological stress is observed in this fish upon exposures to short duration (<3h) of both – moderate and acute hypoxia but not to exposures to long duration (8-12h). The results of this study are interesting as to how the duration and intensity of a stressor may exert variable influences in fish. The findings also appear significant in the light of adaptive mechanisms for stress tolerance operating in organisms.