Effects of heat stress on the renal and branchial carbohydrate metabolism and antioxidant system of Antarctic fish
The objective of the present study was to assess the effect of short-term (2–144 h) heat stress (8 °C) on energy production processes and antioxidant defense systems in the kidneys and gills of Notothenia rossii and Notothenia coriiceps. Heat stress affected energy metabolism and oxidative stress parameters in a time-, tissue-, and species-dependent manner, and gills were more sensitive than kidneys to heat stress. N. rossii kidneys were able to stabilize carbohydrate metabolism after 12 h of heat stress, whereas the glycogen levels in N. coriiceps kidneys fluctuated in response to varying glucose-6-phosphatase (G6Pase) levels. The gills of N. rossii were able to stabilize their energy demand and aerobic metabolism under heat stress, whereas in the gills of N. coriiceps, changes in carbohydrate metabolic pathways depended on the exposure time: initially, anaerobiosis was activated after 6 h; the energy demand, characterized by glycogen consumption, increased after 72 h, and aerobic metabolism was activated within 144 h. With regard to the antioxidant defenses of the N. rossii kidney, it was found that levels of antioxidant enzymes were reduced during the first hours of heat stress, contributing to increased lipid peroxidation, whereas N. coriiceps kidneys did not show signs of oxidative damage. The gills of N. rossii exhibited more pronounced oxidative damage in response to heat stress than those of N. coriiceps despite the presence of increasing levels of antioxidants, likely due to tissue hypoxia.