Histopathology and oxidative stress responses of Nile tilapia Oreochromis niloticus exposed to temperature shocks

Temperature shock is a major natural cause of mass mortality of global fish. Nile tilapia Oreochromis niloticus, one of the most widely cultured species, with high resistance against severe environmental conditions, is also affected by rapid temperature changes. This research was conducted to investigate histopathological changes and oxidative stress in O. niloticus in response to temperature shock. The malondialdehyde levels in the serum, gills and brain, the histopathology of the gills and brain, and the histochemical characterization of the gills' mucosubstances were measured in the fish exposed to heat shock and cold shock conditions. The results showed that the fish could not survive under 37 degrees C for 24 hours. Malondialdehyde levels in the gills, brain and serum increased significantly when compared to those of the controls. Moreover, histopathological changes and a decrease in the number of neutral and acidic mucous cells was observed in the gills of fish in both the heat shock and cold shock groups. Histopathological alteration, vacuolated neuropil in the brain, was observed only in the fish in the cold shock groups. The results from this study indicate that rapid 4 degrees C changes in water temperature (25-21 and 25-29 degrees C) evoked oxidative stress and histological damage to O. niloticus, whereas extreme 12 degrees C changes (25-13 and 25-37 degrees C) severely affected their oxidative stress and histopathological condition.