Extraintestinal calcium uptake in the killifish, Fundulus heteroclitus.

Extraintestinal calcium influxes were measured in the killifish, Fundulus heteroclitus, in solutions with different calcium concentrations, from distilled water level (near 0) to seawater level (approximately 12 mM). The extraintestinal influx is modified by the concentration of calcium in the medium during the adaptive period. In freshwater-adapted fish, calcium depletion resulted in an increase in calcium uptake. Such an adaptation was not observed in calcium-depleted fish in artificial calcium-deficient seawater. Calcium depletion in either medium seems to increase the calcium permeability. No correlation was found between Ca-ATPase activity in the gill tissue and calcium uptake.