Redband Trout Cardiac Function under Hypoxic and Thermal Stress

Aquatic hypoxia, or dissolved oxygen (DO) deficiency, has increased in frequency with rising water temperatures as a result of climate change. Temperature and DO are important factors that can affect many biotic processes for salmonids. Fish can adjust to environmental variables such as temperature change and hypoxia using phenotypic plasticity. Redband trout (Oncorhynchus mykiss gairdneri) have desert, cool montane, and cold montane ecotypes in Idaho. This research analyzed the effects of hypoxia and thermal stress, both in combined and isolated tests, on age-1 redband trout. These fish have been acclimated in a common garden at 21°C and 15°C, to model desert and cold montane habitats, respectively. The experiment examined cardiac phenotypic response using an electrocardiogram (ECG) to measure the heart rate of individuals when exposed to hypoxic conditions and acute thermal stress. The treatment started each individual’s acclimation temperature and 100% DO saturation. Hypoxia was initiated by bubbling N2 gas into the water at a constant rate to reduce DO to 50% saturation. The redband trout then experienced a temperature increase until their ECG displays arrhythmia, which marks the endpoint of the study. The results will show the heart rate at cardiac arrhythmia for each individual. Phenotypic plasticity is possible for hypoxia and acute temperature tolerance in redband trout. This could imply persistence for the species. However, if the combination of hypoxic and thermal stress has a synergistic effect, climate change could have worse consequences for fish than previously understood.