Effects of short-term thermal stress on the plasma biochemical profiles of two Antarctic nototheniid species

Thermal elevation records in the Austral Ocean have raised questions about the physiological impacts on Antarctic organisms which have evolved under cold and stable water temperatures. Some notothenioid fishes exhibit species-specific responses to elevated temperature, yet the mechanisms involved in restoring homeostasis are unclear. Our study focused on the physiological effects of short-term (2–144 h) exposure to water temperatures of 8 °C on the plasma biochemical profiles of Notothenia coriiceps and Notothenia rossii, species that are abundant in Admiralty Bay, King George Island, Antarctic Peninsula, a region where increasing temperatures have been detected. Despite being phylogenetically similar, these species responded differently to thermal stress. N. rossii showed no changes in cortisol levels, and transient hyperglycemia was likely triggered by elevated catecholamine levels; conversely, metabolic and antioxidant defense parameters were unaffected. Increased gill Na+/K+-ATPase activity was observed only in N. rossii after 24 h at 8 °C, which assists in maintaining ionic homeostasis. In N. coriiceps, cortisol accurately indicated thermal stress. Increased cortisol levels in N. coriiceps additionally resulted in transient secondary responses such as hyperglycemia and hyperlactemia, as well as reduced levels of total protein, globulins and triglycerides. Unlike in N. rossii, catalase activity in N. coriiceps was modulated at 8 °C, and this parameter is thus considered a good biomarker of thermal stress. Results suggest that N. coriiceps is more sensitive to thermal stress than is N. rossii and that the former is a potential bioindicator for Admiralty Bay.