Defecation and the fate of dietary sodium in the common killifish (Fundulus heteroclitus macrolepidotus Walbaum, 1792)

While uptake of Na+ from the water is well-characterized in fish, little is known about the uptake of Na+ from the diet. A method involving radiolabeling of the diet with [22Na+] and [3H] PEG-4000 has been developed to study this process, and to separate the systemic efflux of absorbed [22Na+] via gills and kidney from the potential efflux of [22Na+] into the water via defecation. Killifish were acclimated to 10% sea water, a typical salinity …