The effect of fluctuating salinity on the tissue water content of eight species of bivalve molluscs

Abstract

1. Eight species of bivalve molluscs were exposed both to gradual and abrupt salinity fluctuations and the changes in their tissue water content measured. 2. In 7 of the species studied the tissue water volume varied, but only by a small amount, compared to the amplitude of change of the external medium. 3. NormalMercenaria mercenaria showed no significant changes in tissue water level when exposed either to the gradual or the abrupt salinity regime. 4. Mytilus edulis exposed to fluctuating salinity for 1 week prior to sampling showed no significant changes in tissue water content. 5. Wedged-open specimens showed greater changes in tissue water content than did normal animals. 6. The tissue water content of low salinity acclimatedMya arenaria increased more quickly in high salinities and decreased more slowly in low salinities than did high salinity acclimatedMya. The amplitude of change in tissue water content was greater in low salinity acclimated animals than in high salinity ones. 7. None of the species studied showed an overshoot of the original tissue water content and it seems unlikely that volume regulation by animals exposed to short term salinity fluctuation is due to solute extrusion. 8. A model is presented to characterize each species according to its characteristic permeability.