Effects of temperature on sustained swimming performance and swimming kinematics of the chub mackerel Scomber japonicus

摘要

The effects of a VC difference in water temperature on maximum sustained swimming speed, swimming energetics and swimming kinematics were measured in the chub mackerel Scomber japonicus (Teleostei: Scombridae), a primarily coastal, pelagic predator that inhabits subtropical and temperate transition waters of the Atlantic, Pacific and Indian Oceans. New data for chub mackerel acclimated to 18degreesC are compared with published data from our laboratory at 24degreesC. Twelve individuals acclimated to each of two temperatures (15.6-26.3cm fork length, FL, and 34-179g at 18degreesC; 14.0-24.7cm FL and 26-156g at 24degreesC) swam at a range of speeds in a temperature-controlled Brett-type respirometer, at the respective acclimation temperature. At a given fish size, the maximum speed that S.japonicus was able to maintain for a 30-min period, while swimming steadily using slow, oxidative locomotor muscle (U-max,U-c), was significantly greater at 24 than at 18degreesC (52.5-97.5cms(-1) at 18degreesC and 70-120cms(-1) at 24degreesC). At a given speed and fish size, the rate of oxygen consumption ((V)overdotO(2))was significantly higher at 24 than at 18degreesC because of a higher net cost of transport (1073-4617jkm-lkg7l at 18degreesC and 2708-14895Jkm(-1)kg(-1) at 24degreesC). Standard metabolic rate, calculated by extrapolating the log(V)overdot(2) versus swimming speed relationship to zero speed, did not vary significantly with temperature or fish mass (126.4+/-67.2 MgO(2)h(-1)kg(-1) at 18degreesC and 143.2+/-80.3mgO(2)h(-1)kg(-1) at 24degreesC; means S.D., N=12). Swimming kinematics was quantified from high-speed (120Hz) video recordings analyzed with a computerized, two-dimensional motion-analysis system. At a given speed and fish size, there were no significant effects of temperature on tail-beat frequency, tail-beat amplitude or stride length, but propulsive wavelength increased significantly with temperature as a result of an increase in propulsive wave velocity. Thus, the main effects of temperature on chub mackerel swimming were increases in both Un(max,c) and the net cost of swimming at 24degreesC. Like other fishes, S. japonicus apparently must recruit more slow, oxidative muscle fibers to swim at a given sustainable speed at the lower temperature because of the reduced power output. Thus, the 24degreesC mackerel reach a higher speed before they must recruit the fast, glycolytic fibers, thereby increasing U-max,U-c at 24degreesC. By quantifying in vivo the effects of temperature on the swimming performance of an ectothermic species that is closely related to the endothermic tunas, this study also provides evidence that maintaining the temperature of the slow, oxidative locomotor muscle at 6degreesC or more above ambient water temperature in tunas should significantly increase sustainable swimming speeds, but also increase the energetic cost of swimming, unless cardiac output limits muscle performance.