Respiratory Quotients in Goldfish and Rainbow Trout

The respiratory quotients (R.Q.) of goldfish and rainbow trout were measured at 20 and 15 C respectively under spontaneous and forced activity. In goldfish spontaneously active and acclimated to air saturation the R.Q. was 1.02 in ambient oxygen above 50% air saturation and rose to 1.94 below 25% air saturation. Rainbow trout under similar conditions displayed respective R.Q.'s of 0.96 and 1.4. The latter R.Q. could be sustained only for a short time. In both species the metabolic rate dropped at oxygen concentrations below 50% air saturation but spontaneous activity remained high. Goldfish acclimated to 15% air saturation displayed the same R.Q. as unacclimated fish and thus did not display any increase in anaerobic capacity. When forced to swim steadily in water above 50% air saturation both species showed an initial anaerobic phase. This phase was less marked in the rainbow trout and was followed by an aerobic steady state except that at low swimming speeds the goldfish appeared to continuously derive some energy anaerobically. At oxygen concentrations below 50% air saturation the R.Q. of goldfish increased with decreasing concentration during steady swimming. At the single level of steady swimming effort at which comparisons were made, the R.Q. of goldfish did not change with acclimation to 15% air saturation but the rate of oxygen consumption fell to about 50% of the value before acclimation. The rainbow trout was not acclimated to low oxygen for any test.