Cardiorespiratory status of triploid brown trout during swimming at two acclimation temperatures

At 14degreesC, standard metabolic rate (75.1 mg O-2 h(-1) kg(-1)), routine metabolic rate (108-8 mg O-2 h(-1) k(-1)), active metabolic rate (c. 380 mg O-2 h(-1) kg(-1)), critical swimming speed (U-crit 1.7 BL s(-1)), heart rate 47 min(-1)), dorsal aortic pressure (3.2 kPa) and ventilation frequency (63 min(-1)) for triploid brown trout Salmo trutta were within the ranges reported for diploid brown trout and other salmonids at the same temperature, During prolonged swimming (c. 80% U-crit), cardiac output increased by 2.3-fold due to increases in heart rate (1.8-fold) and stroke volume (1.2-fold). At 18degreesC, although standard and routine metabolic rates, as well as resting heart rate and ventilation frequency increased significantly, active metabolic rate and certain cardiorespiratory variables during exercise did not differ from those values for fish acclimated to 14degreesC. As a result, factorial metabolic scope was reduced (2.93-fold at 18degreesC v. 5.13-fold at 14degreesC. Therefore, it is concluded that cardiorespiratory performance in triploid brown trout was not unusual at 18degreesC, but that reduced factorial metabolic scope may be a contributing factor to the mortality observed in triploid brown trout at temperatures near 18degreesC. (C) 2002 The Fisheries Society of the British Isles.