Cardiorespiratory physiology and swimming energetics of a high-energy-demand teleost, the yellowtail kingfish (Seriola lalandi).

This study utilizes a swimming respirometer to investigate the effects of exercise and temperature on cardiorespiratory function of an active teleost, the yellowtail kingfish (Seriola lalandi). The standard aerobic metabolic rate (SMR) of S. lalandi (mean body mass 2.1 kg) ranges from 1.55 mg min(-1) kg(-1) at 20 degrees C to 3.31 mg min(-1) kg(-1) at 25 degrees C. This 2.1-fold increase in SMR with temperature is associated with a 1.5-fold increase in heart rate from 77 to 117 beats min(-1), while cardiac stroke volume remains constant at 0.38 ml beat(-1) kg(-1) and the difference in oxygen content between arterial and mixed venous blood [(Ca(O2)-Cv(O2))] increases marginally from 0.06 to 0.08 mg ml(-1). During maximal aerobic exercise (2.3 BL s(-1)) at both temperatures, however, increases in cardiac output are limited to about 1.3-fold, and increases in oxygen consumption rates (up to 10.93 mg min(-1) kg(-1) at 20 degrees C and 13.32 mg min(-1) kg(-1) at 25 degrees C) are mediated primarily through augmentation of (Ca(O2)-Cv(O2)) to 0.29 mg ml(-1) at 20 degrees C and 0.25 mg ml(-1) at 25 degrees C. It seems, therefore, that the heart of S. lalandi routinely works close to its maximum capacity at a given temperature, and changes in aerobic metabolism due to exercise are greatly reliant on high blood oxygen-carrying capacity and (Ca(O2)-Cv(O2)). Gross aerobic cost of transport (GCOT) is 0.06 mg kg(-1) BL(-1) at 20 degrees C and 0.09 mg kg(-1) BL(-1) at 25 degrees C at the optimal swimming velocities (U(opt)) of 1.2 BL s(-1) (opt) and 1.7 BL s(-1), respectively. These values are comparable with those reported for salmon and tuna, implying that the interspecific diversity in locomotor mode (e.g. subcarangiform, carangiform and thunniform) is not concomitant with similar diversity in swimming efficiency. A low GCOT is maintained as swimming velocity increases above U(opt), which may partly result from energy savings associated with the progressive transition from opercular ventilation to ram ventilation.