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 Ca2+ (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 Ca2+ (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 K-42 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 Ca2+. 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 KCI to the water, indicating chat the net loss of Ki was probably not the cause of death.