Some aspects of water and sodium exchange of freshwater crocodilians in fresh water and sea-water: Role of the integument

Abstract

1. 1. Water efflux and sodium influx and efflux were measured in Alligator mississippiensis and Crocodylus moreletii in fresh water and/or sea-water. 2. 2. Overall body water effluxes in these two species are similar in fresh or sea-water. 3. 3. A large proportion of the water turnover in Alligator occurs through the integument. 4. 4. There are marked regional differences in in vitro measures of water permeability of Alligator, with oral epithelia greatly exceeding that of the ventro-lateral integument. 5. 5. Values of integumental water flux in Alligator are much higher than those for sodium. 6. 6. Overall body sodium influxes in sea-water for these two crocodilians (unfed) were moderate for freshwater reptiles, but higher than in most estuarine and marine forms. 7. 7. Most of the sodium uptake from sea-water occurs in the cephalic region, as drinking or diffusion across epithelia. 8. 8. The integument of Alligator has a very low permeability to sodium; oral epithelia are much higher. 9. 9. Fed crocodilians in fresh water have a higher sodium efflux than when unfed. 10. 10. Alligator exposed to sea-water can increase body sodium efflux if there is also access to fresh water. However access to 9 ppt instead of fresh water depresses this response. 11. 11. Based on integumental water fluxes, Alligator is not physiologically a highly aquatic form comparable to the freshwater turtles Chelydra and Trionyx, or the freshwater snake Regina. This belies an external morphology that is extensively modified for an aquatic life.