Interaction of oxygen supply, oxidative stress, and molecular defence systems during temperature stress in fishes

Oxygen is the essential substrate for oxidative energy production, but oxygen exposure has to be limited because of the damaging effects of reactive oxygen specie (ROS). Thus, the regulation of oxygen homeostasis within a narrow physiological range is crucial for all aerobic life. In marine ectotherms, temperatures outside the species specific optimum range, which is enclosed by the pejus temperatures (Tp), are supposed to cause progressively decreasing oxygen levels in body fluids and tissues, i.e. functional hypoxia. When critical temperatures (Tc) are reached, transition to anaerobic energy production can be observed. It was hypothesised that temperature induced hypoxia entails oxidative stress, i.e. unbalanced ROS production. Moreover, temperature-induced hypoxia was suggested to induce physiological adjustments mediated by the hypoxia inducible transcription factor (HIF-1), i.e. the master regulator of oxygen homeostasis. In my doctoral studies investigated the effect of temperature stress, anticipated to induce functional hypoxia, on a wide array of oxidative stress parameters and on molecular defence systems, especially the hypoxic response, in marine fish from different latitudes. Different time scales of temperature exposure were studied, from temperature adaptation (evolutionary effects), seasonal acclimatisation and laboratory acclimation (long-term temperature effects of several weeks) to few hours of experimental temperature exposure (short-term effects). Moreover, the investigated temperature range, starting from optimal control conditions increasing to pejus, critical and finally extreme temperatures, allowed for distinguishing various degrees of functional hypoxia