Some aspects of electrolyte and water balance in three estuarine reptiles, the diamondback terrapin, American and “salt water” crocodiles

Abstract

1. 1. Diamondback terrapins ( Malaclemys terrapin) were caught in the wild at salinities between 11·3 and 31·8%. 2. 2. Acclimation of terrapins to sea water caused a 2·4-fold increasein the Na concentration of orbital fluid. Two species of crocodiles ( Crocodylus acutus, C. porosus) showed only a 1·4-fold increase. 3. 3. Sea water acclimation in terrapins caused a rise in plasma Na concentration. The increase was relatively small over a 6-week period of acclimation. Wild-caught terrapins had a higher plasma Na concentration. 4. 4. Maximum rates of salt gland secretion in sea water-acclimated terrapins measured by a head rinse technique varied from 16·8 to 26·6 μmoles Na/100 g hr. In fresh-water-acclimated animals secretion was less than 1 μmole Na/100 g hr. The estuarine terrapin thus has a salt gland intermediate in secretory capacity between those of terrestrial and marine reptiles. 5. 5. Preliminary evidence provides little support for the concept that American and “salt water” crocodiles utilize salt glands as a major pathway of electrolyte excretion, although these crocodiles are fairly tolerant of exposure to sea water.