title: Drinking and water permeability in the Pacific hagfish, Eptatretus stoutii.
abstract: Hagfish are osmoconformers, maintaining an internal osmolality that matches their seawater habitats. Hagfish would, therefore, appear to have no physiological need to drink, but previous studies are equivocal regarding whether drinking in hagfish occurs. The current study addressed this knowledge gap, by examining drinking and water permeability in the Pacific hagfish, Eptatretus stoutii. One-third of analysed hagfish were shown to accumulate radiolabelled drinking rate markers (tritiated inulin and polyethylene glycol-4000) in their gut tissues; however, this was attributed to the presence of markers in the blood perfusing the digestive tract, following absorption through paracellular pathways at the gill. No accumulation of marker was observed in hagfish subjected to more dilute (75% seawater) or more concentrated (125% seawater) media. Diffusive water efflux, measured by tritiated water washout, was shown to be very high, with 50% of body water exchanged within 14 to 16 min, depending on exposure salinity. In full-strength seawater, the total exchangeable pool of water was 78% of hagfish mass. We conclude that hagfish do not drink, and their high water permeability is likely to result in rapid osmotic equilibration under circumstances where perturbations may occur.
authors.affiliation: Faculty of Science and Technology and Athabasca River Basin Research Institute, Athabasca University, 1 University Drive, Athabasca, AB, T9S 3A3, Canada. cglover@athabascau.ca.|Bamfield Marine Sciences Centre, Bamfield, BC, Canada. cglover@athabascau.ca.|Department of Biological Sciences, University of Alberta, Edmonton, Canada. cglover@athabascau.ca.
authors.forename: Chris N
authors.initials: CN
authors.lastname: Glover
authors.affiliation: Bamfield Marine Sciences Centre, Bamfield, BC, Canada.|Department of Zoology, University of British Columbia, Vancouver, Canada.|Department of Biology, McMaster University, Hamilton, Canada.
authors.forename: Chris M
authors.initials: CM
authors.lastname: Wood
authors.affiliation: Bamfield Marine Sciences Centre, Bamfield, BC, Canada.|Department of Biological Sciences, University of Alberta, Edmonton, Canada.
authors.forename: Greg G
authors.initials: GG
authors.lastname: Goss
mesh_terms: D000818:Animals; D004326:Drinking; D006196:Hagfishes / Q000378:metabolism / Q000502:physiology*; D007444:Inulin / Q000097:blood / Q000493:pharmacokinetics; D010539:Permeability; D011092:Polyethylene Glycols / Q000493:pharmacokinetics; D014316:Tritium; D014867:Water / Q000378:metabolism*
chemical_list: D014867:Water; D014316:Tritium; D011092:Polyethylene Glycols; D007444:Inulin
keywords: Drinking; Hagfish; Osmoconforming; Salinity; Water permeability