UNIDIRECTIONAL FLUXES OF NA+, CL- AND WATER IN FINGERLING CHANNEL CATFISH, ICTALURUS-PUNCTATUS

1. 1. The influx of Na+ and Cl-(as 22Na+ and 36Cl-1) was measured in fingerling channel catfish (Ictalurus punctatus) and was found to be equivalent in a 7-8 g fish to about 20 and 40%, respectively, each day of their total body Na or Cl. In the smallest fish (l g), the rate of flux was 3-4 times as great as in larger (15g) ones. 2. 2. Unidirectional flux of water (as efflux of 3H-water) was very rapid, equivalent to about 3 times the total body water each hour. 3. 3. Drinking was relatively small equivalent to about 2.5% of the body weight each day (6% at pH 5) and so contributed little to the above fluxes, which presumably mainly occurred across the gills and possibly the skin. 4. 4. Influx of Na+ was reduced when the Ca2+ concentration was increased from 0.1 to 3 mM. Changes of pH between 8.3 and 5 and the presence of 0.01 mM A13+ such as may result from "acid rain" did not change Na influx. 5. 5. Efflux of Na+ was increased when the pH was decreased from 7.3 to 5, but neither Ca2+ (3 mM) nor Al3+ (0.01 mM at a pH of 5) had a significant effect. 6. 6. The unidirectional flux of water was reduced by 0.01 mM Al3+ at pH 5, but it was unchanged by a pH of 5 alone or 3 mM Ca2+. © 1990.