Scientific Journal Article Summary
Influence of Swimming Speed on Metabolic Rates of Juvenile Pacific Bluefin Tuna and Yellowfin Tuna
Jason M. Blank, Charles J. Farwell, Jeffery M. Morrissette, Robert J. Schallert, Barbara A. Block
Physiological and Biochemical Zoology (2007) 80:167–177
Tunas have a remarkable suite of morphological and physiological traits that enhance swimming performance, including a bullet-shaped body, thrust-producing lunate tail, and high cardiac output and metabolic rate. Bluefin tuna are even more specialized because they are endothermic, or warm-bodied, and therefore have higher body temperatures, heart rates, and cardiac outputs than tropical tunas like yellowfin. Bluefin tuna swim in near-freezing temperatures yet can maintain their muscle temperature up to 70ºF above the ambient water temperature.
To test the hypothesis that bluefin have higher metabolic rates than tropical tunas, this study measured the oxygen consumption rate of juvenile Pacific bluefin and yellowfin tuna swimming in a respirometer, a tank that allows monitoring of a fish’s physiology while it is swimming. A higher rate of oxygen consumption would imply a higher metabolism.
Bluefin tuna had higher oxygen consumption rates, and therefore higher metabolic rates, than yellowfin tuna at all swimming speeds tested. The minimum metabolic rate of swimming bluefin was 37% higher than that of yellowfin.
At a given speed, bluefin swam with higher tailbeat frequencies and shorter stride lengths (i.e., distance traveled per tail thrust) than yellowfin. The cost of transport, or oxygen consumption per distance traveled, was also higher in bluefin. The higher tailbeat frequency likely explains the bluefin’s higher metabolic rate and higher cost of transport.
Maximum speed for both species was the same due to limitations of the respirometer motor. Minimum speed was lower in yellowfin than in bluefin, likely due to the yellowfin’s larger pectoral fins, which may allow them to remain vertical at slower speeds. Individuals of both species experienced higher metabolic rates at slower speeds due to inefficiency.
The higher oxygen consumption recorded in Pacific bluefin tuna is consistent with the elevated cardiac performance and warm-bloodedness of these fish. Elevated metabolic rate is likely an essential component of the bluefin tuna’s ability to regulate its body temperature. These physiological traits likely underlie the bluefin tuna’s expanded range into cooler waters relative to tropical tuna species.
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| A tuna swimming in a respirometer. |