Ion Regulation, Acid/Base Balance and Gas Exchange Interactions in Salmon Across Salinities

Abstract

Migration between freshwater and sea water in diadromous fishes requires substantial changes in branchial, renal and intestinal regulation. Since little is known about osmoregulation in fishes in brackish water, where the gradients for water and ion movements are reduced, we investigated the organ‐specific transitions in osmoregulation across salinities, and how these may impose tradeoffs with brachial gas‐exchange and organismal acid/base‐balance. We acclimated Coho salmon to fresh‐, brackish‐, and seawater for a full year, and then measured ion‐ and acid/base‐regulation and gas‐exchange in fishes instrumented with vascular and urinary bladder cannulas. We show that glomerular filtration rate and urine production gradually decrease with increases in salinity, while drinking rates do not increase until salinities exceed isosmotic, showing that transitions in osmoregulatory function of the kidneys and gastrointestinal tract are not initiated at the same salinity. Further, we show that arterial blood gas status is identical across salinities, suggesting that branchial remodeling during salinity acclimation does not affect gas‐exchange. Lastly, we show that plasma ion composition differs across salinities and is associated with different set‐points for intra‐ and extracellular pH‐regulation. These data provide insight into compromises between ion regulation, acid/base balance and gas‐exchange in euryhaline animals across salinities.Support or Funding InformationCD is supported by the Carlsberg Foundation and the research was funded by a Natural Sciences and Engineering Research Council of Canada, Strategic Partnership Grant.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.