ION-TRANSPORT IN THE FRESH-WATER ZEBRA MUSSEL, DREISSENA-POLYMORPHA

The blood solute concentration (36 mosm) of pondwater acclimated zebra mussels is among the lowest found in freshwater bivalves. Blood ion concentrations were Na (11-14 mM) and Cl (12-15 mM), with lesser amounts of Ca (4-5 mM), HCO3 (about 2-4 mM), and K (0.5 mM). Sodium, Ca and Cl transport rates were 20-30 mueq (g dry tissue . h)-1 for pondwater acclimated mussels. The influx of both Na and Cl was stimulated by exogenous serotonin (0.1 mM). Sodium transport in zebra mussels was not inhibited by amiloride. Zebra mussels became isosmotic in 30 mM NaCl solutions and did not survive beyond a week in 45 mM NaCl. Zebra mussels are well adapted to their dilute freshwater habitat, but are more stenohaline than other freshwater bivalves as reflected by their intolerance of elevated ion concentrations in the bathing solution.