The metabolic rates (V(dot)O2) of three tropical tunas [yellowfin tuna (Thunnus albacares), kawakawa (Euthynnus affinis) and skipjack (Katsuwonus pelamis)] were estimated using a large water-tunnel respirometer. Experiments lasting up to 31 h were used to determine the effects of velocity (U) on tuna V(dot)O2 over a range of U (17-150 cm s-1) and temperatures (18­30°C). Replicate tests were carried out on several fish. The swimming V(dot)O2 of yellowfin is temperature-dependent (Q10=1.67, determined over intervals of 3­5°C). For yellowfin and skipjack, it was also possible to partition metabolic costs between maintenance and locomotion. The standard metabolic rate (SV(dot)O2) was estimated by extrapolation of the U/V(dot)O2 function to U=0. Comparisons of SV(dot)O2 for different size groups of yellowfin show that the mass-specific scaling exponent for V(dot)O2 is -0.40. The SV(dot)O2 of tuna is comparable to values determined previously by stasis respirometry and is approximately three times higher than that of salmonids. Further comparisons with salmonids show that the slope of the U/V(dot)O2 function is less for tunas, which demonstrate a greater swimming efficiency.

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