Deleterious impacts of heat stress on steroidogenesis markers, immunity status and ovarian tissue of Nile tilapia (Oreochromis niloticus)

The water temperature of aquacultures is a primary factor of fish welfare, reproductive patterns, and immunity. To elucidate the molecular and biological processes of the temperature modulation of reproduction and immunity, female Nile tilapia (190 +/- 10g) were allocated into five groups following acclimatization (150 females, three replicates, each n = 10). Each group was subjected to various temperatures (28 degrees C, 30 degrees C, 32 degrees C, 34 degrees C, and 37 degrees C), the group at 28 degrees C representing the control. Their serum levels of estradiol, cortisol, and vitellogenin were measured as well as serum triiodothymnine (T3) hormone, thyroxine (T4) hormone, and non-specific immunity (phagocytic and lysozyme activity). In addition, stemidogenic acute regulatory protein (STAR), vitellogenin gene receptor, and heat shock protein 70 (HSP70) gene expression were evaluated. The serum levels of estradiol, cortisol, and vitellogenin markedly declined (P < 0.05) in fish group at higher temperatures. In addition to T3, T4 was significantly affected (P < 0.05) in the control group. The expressions of the STAR gene (steroidogenesis) and vitellogenin receptors were also considerably down-regulated. The histopathological photomicrograph of fish subjected to high water temperature revealed injuries in ovary tissues, demonstrating its harmful effects. The experimental results verified the possible role of water temperature as a main stressor on Nile tilapia' physiology through modulation of steroidogenesis-related gene expression and immunity.