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

Chris M. Wood, Carol Bucking

Research output: Contribution to journalArticlepeer-review

1 Scopus citations


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 for this estuarine fish where they are hyperosmotic to the environment. The fish were fed a single meal (0.81% ration, containing 5.09μmol total Na +gbody weight -1) of re-pelleted food labeled with both radiotracers. Effluxes into the water were monitored for 48h. Sharp increases in [ 3H] PEG-4000 appearance provided a clear definition of defecation events, which started at about 7h post-feeding and finished by 16h, with the midpoint at 11.5h. In contrast, the evolution of [ 22Na +]-radioactivity in the water showed a smooth curvilinear relationship starting at 3h, with a gradually declining slope through 48h. There was no efflux of [ 22Na +] associated with defecation events, showing that all [ 22Na +] was quickly absorbed from the meal. By 48h, about 50% of the consumed [ 22Na +] had been excreted to the external water by systemic efflux. The efflux relationship was best described by a two-phase exponential relationship, with a breakpoint at about 13h post-feeding. The first phase (rate constant 0.0309h -1) corresponded to branchial efflux of dietary [ 22Na +] equilibrated with the exchangeable whole body Na + pool, while the second phase was much slower (0.0114h -1). These results emphasize the importance of dietary Na + when the killifish is hyper-regulating, and provide a method applicable to a wide range of conditions, ions, and species.

Original languageEnglish (US)
Pages (from-to)53-57
Number of pages5
JournalJournal of Experimental Marine Biology and Ecology
StatePublished - Dec 1 2012


  • [ Na ]
  • [ H] PEG-4000
  • Feeding
  • Gills
  • Intestine
  • Ionoregulation

ASJC Scopus subject areas

  • Aquatic Science
  • Ecology, Evolution, Behavior and Systematics


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