Potassium flux in juvenile striped bass (Morone saxatilis): influence of external concentrations of sodium chloride and calcium.

Whole-body influx and efflux of K(+) were determined for 25-day-old striped bass,Morone saxatilis, in conditions that simulated harvesting fish from ponds. During the first 5h in fresh water with combined high NaCl (80 mM) and low Ca(2+) (0.12 mM) concentrations, a combination that is acutely lethal to this age of striped bass, K(+) influx for fish in 0.07 mM K(+) was 21±1.7 (SEM) compared to 3.4±0.33 nmol g(-1) h(-1) for fish in water with low Na(+) (0.25 mM) or high Ca(2+) (2.5 mM) concentrations. Influx of K(+) was inhibited during the first few hours after fish were placed in flux chambers. Potassium efflux as percentage of(42)K lost per hour was two-fold higher from fish in the high Na-low Ca treatment compared to fish in low concentrations of Na(+) or high concentrations of Ca(2+). Potassium efflux was probably much greater than influx, but exact values for efflux could not be calculated from the data available. Survival of fish in water with high Na-low Ca was not increased by addition of KCl to the water, indicating that the net loss of K(+) was probably not the cause of death.