A size dependent oxygen consumption of Ascidiella aspersa was registered in sub and supra normal salinities of 30, 25, 20 and 40 %o. Further a decrease in oxygen uptake occurred at both sub and supra normal salinities. It was found that the percentage oxygen uptake of small animal was higher than large animal. In subnormal salinities A. aspersa showed contraction of its body and siphons.

The amount of water transported by Ascidiella aspersa was a function of size in 34 %o and 30°C, the regression coefficient being 0.6975. The volume of water transported decreased with decrease or increase of salinity, but the size dependent pattern of water transport was noted in all salinities except . 20 %_o where there was no increase in transport with increase in size of animal. The pumping rate of larger animal was comparatively lower than that of small animal. The low water transport was associated with partial closure of siphons and shrinking of the body.

Calculation of the amount of water transported per ml of oxygen consumid by the animal showed decrease in sub and supra normal salinities, but the decrease was not proportionate to the corresponding decrease in salinities. The amount of oxygen uptake per litre of water transported was found to increase with change in salinities. The physiological stress due to reduction in salinity was observed to be compensated by the increase in the efficiency of oxygen extraction. However, it was found that such an increase in efficiency was not proportional to the magnitude of decrease in salinity. It is likely that decrease in water transport alone may not account for the low oxygen uptake by the animal in sub and supra normal salinities.