Effect of abrupt change in the salinity of the environment on plasma electrolytes, urine volume, and electrolyte excretion in channel catfish, Ictalurus punctatus

Abstract

1. 1. Plasma Na levels of fish transferred from fresh water to salt water remained hypernatremic to the environment; however, plasma Cl remained at or near the environmental level. 2. 2. Acclimation in salt water hyperionic to plasma ions required 15 days; in a medium isonatremic and hyperchloremic acclimation required 3 days, but in isoionic medium no change in plasma ions occurred. 3. 3. Handling did not affect plasma Na and Cl of fresh water fish. 4. 4. Acclimation in isoionic salt water had no effect on the response of plasma electrolytes to a hyperionic medium. 5. 5. Plasma Na and Cl decreased significantly after transfer from salt to fresh water. 6. 6. Fish in salt water produced small amounts of concentrated urine hypoosmotic to the plasma, compared to the large volume of dilute urine produced by fish in fresh water.