SOME EFFECTS OF TEMPERATURE AND OXYGEN PRESSURE ON THE METABOLISM AND ACTIVITY OF THE SPECKLED TROUT, SALVELINUS FONTINALIS

Abstract

Two levels of oxygen uptake were measured at temperatures from 5 °C. to 24 °C. on yearling speckled trout having a mean weight of 27 gm. These levels were the minimum resting rate in the diurnal cycle (standard rate) and the rate when induced to activity in a rotating chamber (active rate). The trout were thermally acclimated to the temperatures at which the experiments were performed. The standard rate of oxygen uptake increased with increasing temperatures up to the ultimate upper lethal temperature (25.3 °C.). The active rate of oxygen uptake increased with increasing temperatures up to approximately 19 °C. Above this temperature it fell again. The consequence of this difference in the response of the standard and active rates of oxygen rate to temperature is that the difference between these two levels increases rapidly up to a temperature of 16 °C. and falls again thereafter. This is interpreted as indicating that the optimum temperature for the activity of the speckled trout is in the neighborhood of 16 °C. The activity of speckled trout in relation to temperature was measured in terms of the maximum speed that they can maintain indefinitely. This speed was also found to be a maximum at a temperature of 16° to 20 °C., at which region occurs the greatest difference between the standard and active rates of oxygen uptake.The oxygen uptake of active speckled trout was measured over decreasing partial pressures of oxygen, and was found to become dependent on the oxygen pressure below a certain critical level. These critical pressures change with temperature from 100 mm. Hg at 5 °C. to 150 mm. Hg at 24.5 °C. Water containing less than 75% air saturation of oxygen reduces the activity of speckled trout at all temperatures. Above 20 °C. fully saturated water is required to allow full scope to the activity of speckled trout. The minimum oxygen requirements for existence of the speckled trout at the standard metabolic level are estimated to vary from 30 mm. Hg at 5 °C. to 79 mm. Hg at 24.5 °C. It must be emphasized, however, that these values are conservative. The lethal levels of oxygen were measured for speckled trout and found to rise from 19 mm. Hg at 3.5 °C. to 45 mm. Hg at 23 °C.