The respiratory metabolism of temperature-adapted flatfish at rest and during swimming activity and the use of anaerobic metabolism at moderate swimming speeds.

(1) The standard oxygen consumption and the oxygen consumption during measured swimming activity have been determined in three flatfish species at 5, 10 and 15 degrees C. (2) The relationship between weight and standard oxygen consumption for flatfish conform to the general relationship Y = aWb. On an interspecies basis, standard oxygen consumption of flatfish is significantly lower than that of roundfish. (3) A semilogarithmic model describes the relationship between oxygen consumption and swimming speed for the three species. Values for maximum oxygen consumption, metabolic scopes and critical swimming speeds are low in comparison to salmonids. (4) The optimum swimming speeds and critical swimming speeds of flatfish are similar. It is suggested that, over long distances, flatfish adopt a strategy of swimming at supercritical speeds with periods of intermittent rest to repay the accrued oxygen debt. (5) Elevated lactic acid levels in flounder white muscle after moderate swimming indicate an additional 15% anaerobic contribution to the cost of locomotion as calculated from aerobic considerations.