C. Sepulveda et Ka. Dickson, Maximum sustainable speeds and cost of swimming in juvenile kawakawa tuna (Euthynnus affinis) and chub mackerel (Scomber japonicus), J EXP BIOL, 203(20), 2000, pp. 3089-3101
Tunas (Scombridae) have been assumed to be among the fastest and most effic
ient swimmers because they elevate the temperature of the slow-twitch, aero
bic locomotor muscle above the ambient water temperature (endothermy) and b
ecause of their streamlined body shape and use of the thunniform locomotor
mode. The purpose of this study was to test the hypothesis that juvenile tu
nas swim both faster and more efficiently than their ectothermic relatives.
The maximum sustainable swimming speed (U-max, the maximum speed attained
while using a steady, continuous gait powered by the aerobic myotomal muscl
e) and the net cost of transport (COTnet) were compared at 24 degreesC in s
imilar-sized (116-255 mm fork length) juvenile scombrids, an endothermic tu
na, the kawakawa (Euthynnus affinis) and the ectothermic chub mackerel (Sco
mber japonicus), U-max and COTnet were measured by forcing individual fish
to swim in a temperature-controlled, variable-speed swimming tunnel respiro
meter, There were no significant interspecific differences in the relations
hip between U-max and body mass or fork length or in the relationship betwe
en COTnet and body mass or fork length. Muscle temperatures were elevated b
y 1.0-2.3 degreesC and 0.1-0.6 degreesC above water temperature in the kawa
kawa and chub mackerel, respectively. The juvenile kawakawa had significant
ly higher standard metabolic rates than the chub mackerel, because the tota
l rate of oxygen consumption at a given swimming speed was higher in the ka
wakawa when the effects of fish size were accounted for. Thus, juvenile kaw
akawa are not capable of higher sustainable swimming speeds and are not mor
e efficient swimmers than juvenile chub mackerel.