The effect of chronic saline exposure on the electrolyte balance, nitrogen metabolism, and corticosterone titer in the American alligator, Alligator mississippiensis

Abstract

Juvenile alligators were exposed to fresh water, 5, 10, 15 and 20% sea-water for 4 weeks. Hematocrit, plasma corticosterone, plasma and urine osmolality, [Na+], [K+], [Cl-] and uric acid were measured at weekly intervals. Although no change was found in plasma NaCl at 5%, a significant increase in NaCl Urine/Plasma (U/P) ratio was found; however, no further increase in NaCl U/P ratio was found at higher salinities, and plasma NaCl increased with salinity. Plasma corticosterone increased significantly at 10% and greater, and a dramatic increase in plasma and urine uric acid was also found at these salinities. At 10% and greater, alligators ceased feeding and lost up to 27% of their initial body weight. Mortalities occurred during weeks 3 and 4, at 15 and 20%. A possible role for corticosterone in increasing the NaCl U/P ratio is discussed. It is concluded that juvenile alligators are unable to survive chronic exposure to hyperosmotic salinities.