Nitrite-induced reductions in heat tolerance are independent of aerobic scope in a freshwater teleost.

Nitrite is a widespread form of pollution that directly lowers the blood oxygen carrying capacity of aquatically respiring species. It is unknown if this impairment of oxygen transport translates into an increased susceptibility to elevated temperatures. We hypothesised that nitrite exposure would lower blood oxygen carrying capacity and decrease both aerobic scope (maximum-standard metabolic rate) and heat tolerance. To test these hypotheses, juvenile European carp (Cyprinus carpio) were exposed to two levels of nitrite (0 mmol l-1 or 1 mmol l-1) for 7 days and haematological parameters, critical thermal maxima (CTmax) and aerobic scope were assessed. Nitrite exposure reduced total haemoglobin by 32.9%. Aerobic scope remained unchanged in fish exposed to nitrite; however, marked declines in CTmax (1.2°C reduction) were observed in nitrite-exposed fish. These findings demonstrate that nitrite exposure can significantly impair heat tolerance, even when aerobic capacity is maintained.