RELATIONSHIP BETWEEN AMMONIA EXCRETION RATES AND HEMOLYMPH NITROGENOUS COMPOUNDS OF A EURYHALINE BIVALVE DURING LOW SALINITY ACCLIMATION

¹ Department of Zoology, University of Maryland, College Park, Maryland 20742

1. Free amino acid concentrations in the hemolymph increase rapidly in company with a decrease in the tissue free amino acid pool of propped-open M. demissus exposed to low salinity.

2. As acclimation proceeds, blood amino acid concentrations level off and an increase in both hemolymph ammonia concentration and external ammonia excretion occurs.

3. Finally, hemolymph amino acid concentrations decrease toward control levels, followed by hemolymph ammonia concentration and external ammonia excretion rates.

4. Following complete acclimation of mussels to high or low salinity, ammonia excretion rates are the same. However, hemolymph free amino acid concentrations are lower in animals adapted to low salinity.

5. These results show that during acclimation of mussels to low salinity, free amino acids are released intact from the cells into the hemolymph. The subsequent transitory increase in hemolymph ammonia concentrations and external ammonia excretion rates is probably due to degradation of the effluxed amino acids by some specific organ of the body.

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