Routine oxygen uptake (QO2) by yolk-sac and firstfeeding larvae of herring (Clupea harengus L.) and plaice (Pleuronectes platessa L.) was studied after acute change of temperature (8°, 13°, 18°C) and salinity (5, 12.7, 32, 40‰). In both species, QO2 (μl mg-1 dry wt h-1) of both larval stages increased with increasing temperature. Salinity effect on QO2 varied: for yolk-sac larvae of both species a lower QO2 was found at lower combined salinities (5 and 12.7‰); for feeding larvae a lower QO2 was observed at 12.7‰ for both species, possibly due to the relatively smaller size of larvae used at this salinity. For both species, oxygen uptake increased as larvae grew and weight regression coefficients were between 0.74 and 1.33. At 32‰ S, no difference was found in oxygen consumption between species as a function of temperature.