The hypoxic threshold for maximum cardiac performance in rainbow trout Oncorhynchus mykiss (Walbaum) during simulated exercise conditions at 18° C

Perfused rainbow trout Oncorhynchus mykiss hearts exposed to simulated exercise conditions (hypoxia, hyperkalemia and acidosis) at 18 degrees C experienced complete failure of maximum cardiac performance at oxygen tensions < 5.6 kPa and partial failure at < 6.7 kPa. This hypoxic threshold, which occurred in the presence of maximal adrenergic stimulation (500 nM adrenaline), is unusually high compared with previous results at a colder acclimation temperature. Cardiac failure was primarily due to significant decreases (P < 0.05) in heart rate rather than cardiac stroke volume at all hypoxia levels tested. (C) 2007 The Authors. Journal compilation (C) 2007 The Fisheries Society of the British Isles.