ACUTE RESPONSES OF BLOOD PARAMETERS AND COMATOSE EFFECTS IN SALT-ACCLIMATED TILAPIAS EXPOSED TO LOW-TEMPERATURES

1. Changes in the time course of blood hemoglobin, hematocrit, leucocrit, chloride, osmolarity, lactate, glucose and cortisol concentrations were monitored in salt-acclimated tilapias (0, 5, 10 and 20 ppt salinity), Oreochromis niloticus exposed to low temperatures (from 24 degrees C to 12 degrees C). 2. Salinity significantly caused the decreases of hemoglobin concentrations but the increases of lactate, chloride and osmolarity levels in tilapias cultured at 24 degrees C. 3. Low temperature (12 degrees C) caused the increases of glucose, lactate and cortisol levels in the freshwater tilapias while no changes of hemoglobin, hematocrit, chloride and osmolarity were observed. On the contrary, the decreases of hematocrit, leucocrit and lactate levels and the increases of chloride, osmolarity and glucose concentrations were significantly detected in salt-acclimated tilapias exposed to low temperatures. 4. Tilapias cultured in salt water were easy to demonstrate comatose behavior at low temperatures (12-7 degrees C) as compared with freshwater tilapias. 5. It is concluded that low temperatures have the significant effects of either increasing or decreasing direction on the changes of various blood parameters in tilapias depending on the environmental salinity. Salt-acclimated tilapias are suggested to be less tolerant to the low temperatures on the basis of the data of hematocrit, leucocrit, chloride, osmolarity and comatose responses.