Calcium Fluxes in the Teleost Fish Tilapia (Oreochromis) in Water and in Both Water and Air in the Marble Goby (Oxyeleotris) and the Mudskipper (Periophthalmodon)

Abstract

Unidirectional and net extrarenal calcium fluxes in water and in air on wet filter paper were obtained in the mudskipper, Periophthalmodon schlosseri, an obligate air breather, and in the marble goby, Oxyeleotris marmorata, which is fundamentally a water-breathing fish but which can survive extended periods of time on wet filter paper (facultative air breather). For comparison purposes, values were also obtained in water only from tilapia, Oreochromis mossambicus. This fish, which is an obligate water breather and cannot survive long in air, showed rates of influx, efflux, and net flux that were more than double those shown by the two species of gobies in water. In turn, the marble goby had significantly higher rates of influx, efflux, and net flux in water than seen in the mudskipper, Periophthalmodon schlosseri. The difference in net flux between Oxyeleotris and Periophthalmodon was not apparent when the fish were maintained on wet filter paper. On wet filter paper, when branchial/water contact was abolished, both the marble goby and the mudskipper showed significant reductions in unidirectional influx, but the specific activity of the blood was the same as when in water. Normal net flux rates were maintained because efflux decreased to near zero. The results suggest that much of the necessity to maintain an influx of calcium in fish is directly attributable to the necessity to replace calcium lost during branchial irrigation. We conclude, therefore, that these two species can perform cutaneous calcium transport at least when their gills are not exposed to water.