Swimming Speed and Oxygen Consumption in the Bathypelagic MysidGnathophausia ingens

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Abstract
The energetic costs of swimming were determined for the bathypelagic mysid Gnathophausia ingens. Individuals over a large size range spontaneously swam at speeds from 5 to 6.5 cm/s. To maintain this speed, smaller animals swam at much higher relative swimming speeds than did larger animals. Routine rates of oxygen consumption were thus considerably higher in the smaller instars. The relationship between standard rates of oxygen consumption and animal size was slightly less than the standard log-log allometric slope of 0.75. Within the speed range of 0-8 cm/s, oxygen consump tion appeared to increase as a linear function of speed. Cost of transport was very high at low speeds. At 5.5 cm/ s, cost of transport was lower than that measured for other crustaceans, but higher than that of fish. Swimming efficiency increased with speed. While the lower cost of transport and higher swimming efficiency may contribute to G. ingens' reduced rates of oxygen con sumption as compared to those of shallower-living crustaceans, the major factor appears to be G. ingens' lower level of swimming activity.