Interactive effects of temperature and mercury exposure on the stress‐related responses in the freshwater fish Ctenopharyngodon idella.

Aquatic organisms are affected by both water temperature fluctuation and the waterborne pollutants such as heavy metals. In this study, we investigated the effects of water temperature and/or mercury (Hg) on antioxidant parameters (SOD, superoxide dismutase; CAT, catalase; MDA, malondialdehyde; TAOC, total antioxidant capacity), the stress proteins (HSP70, heat shock protein 70; MTs, metallothionein) and the stress hormone (COR, cortisol hormone), as well as the related genes expression of grass carp, Ctenopharyngodon idella. Fish (45.37 ± 3.58 g) were acclimated to 15, 20, 25, 30 or 35°C and co‐exposed to 0.0 or 0.039 mg/L HgCl2 for 4 weeks in triplicates. Three‐way ANOVA revealed that all variables were significantly affected by water temperature, Hg exposure, exposure time and their interactions. The activities of antioxidant enzymes increased significantly by increasing water temperature up to 30°C, after which they decreased significantly at 35°C. The levels of HSP70 and MTs increased with increasing water temperature up to 35°C, but Hg‐exposed fish showed lower levels of two stress proteins as compared to Hg‐free fish groups. Additional, the cortisol content was not positively correlated with temperature. Our data provide evidences that warmer temperatures can potentiate Hg toxicity. Due to the complex mechanism of the toxicity of temperature coupled pollutants on aquatic organisms, more detailed experiments in laboratory need to be performed before these parameters are used as special biomarkers for monitoring aquatic environment. [ABSTRACT FROM AUTHOR]