Glover Chris N, Wood Chris M, Goss Greg G
Faculty of Science and Technology and Athabasca River Basin Research Institute, Athabasca University, 1 University Drive, Athabasca, AB, T9S 3A3, Canada.
Bamfield Marine Sciences Centre, Bamfield, BC, Canada.
J Comp Physiol B. 2017 Dec;187(8):1127-1135. doi: 10.1007/s00360-017-1097-2. Epub 2017 Apr 11.
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.
盲鳗是渗透顺应者，其体内渗透压与海水栖息地相匹配。因此，盲鳗似乎没有生理上的饮水需求，但之前关于盲鳗是否饮水的研究尚无定论。本研究通过检测太平洋盲鳗（Eptatretus stoutii）的饮水情况和水渗透性，填补了这一知识空白。分析显示，三分之一的盲鳗肠道组织中积累了放射性标记的饮水速率标记物（氚标记的菊粉和聚乙二醇-4000）；然而，这归因于鳃部通过细胞旁途径吸收后，灌注消化道的血液中存在这些标记物。在更稀（75%海水）或更浓（125%海水）介质中的盲鳗未观察到标记物的积累。通过氚标记水冲洗测量的扩散性水外流显示非常高，根据暴露盐度，14至16分钟内身体水分有50%被交换。在全强度海水中，可交换的总水量为盲鳗体重的78%。我们得出结论，盲鳗不饮水，其高水渗透性可能会在可能发生扰动的情况下导致快速的渗透平衡。
