Effect of water temperature on the physiological responses in Betta rubra, Perugia 1893 (Pisces: Osphronemidae)

Water temperature is a limiting factor in fish health and plays a crucial role, especially in endemic species that are more sensitive to ambient temperature changes. The objective of the present study was to examine the effects of temperature on growth patterns, survival, blood glucose, gill histology, and erythrocyte cell abnormality of Betta rubra, an endemic species in Aceh and Northern Sumatra, Indonesia. The fish sample was collected from Nagan Raya, Aceh Province, Indonesia. The fish were acclimatized for three days prior to experimental trials at five temperature levels; 24 °C, 26 °C, 28 °C, 30 °C and 32 °C for 14 days. Fish were taken randomly from every treatment to measure blood glucose levels and gill samples were taken at the start and end of the experiment. The results showed the highest survival at a temperature of 28 °C (83.33%). The lowest blood glucose level was also found at a temperature of 28 °C. In addition, an increase and decrease in temperature exceeding 28 °C caused gill damage. Higher temperatures caused an increase in the abnormality of erythrocyte cells, with the highest percentage of abnormality found at 32 °C. Overall, this study confirmed that exposure to lower and higher temperature than the optimal is stressful to B. rubra.