Effect of increasing water temperature on the physiology and gill histology of Barramundi, Lates calcarifer (Pisces, Perciformes) fingerlings

Barramundi, Lates calcarifer is one of the commercial fish in Indonesia and other Southeast Asian countries. The species inhabits the coastal waters and is vulnerable to changes in the terrestrial environment due to coastal degradation, pollution, and global warming. The increase in temperature as a consequence of global warming affects the distribution and survival of aquatic organisms including fish. Therefore, this study aims to examine the effect of increasing water temperatures on the physiological conditions and gill histology of barramundi. The fish were exposed to eight levels of water temperature, ranging from 28oC to 35oC, for 15 days. The initial temperature was 28oC, which increased gradually by 1oC per 12-hour. Blood samples were taken at the end of the experiment for hemoglobin, glucose, cortisol, erythrocytes, leucocytes, and blood abnormality analyses. Gill samples were also taken for histological analysis. The results showed that water temperature significantly affected the level of glucose, cortisol, and erythrocyte cells (P<0.05), but did not influence hemoglobin levels and survival rate (P>0.05). A rapid increase in glucose and cortisol levels was also discovered at a temperature of 31oC above. The highest erythrocyte cell count was found at 35oC, gill cell abnormalities were occurred at temperature of 31oC and above, and the blood abnormalities increased linearly with water temperature. Based on these results, it is concluded that the water temperature did not affect the survival rate but the increase in temperature causes intense physiological stress.