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First published online October 21, 2005
Journal of Experimental Biology 208, 4069-4078 (2005)
Published by The Company of Biologists 2005
doi: 10.1242/jeb.01871

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Ionoregulatory changes in different populations of maturing sockeye salmon Oncorhynchus nerka during ocean and river migration

J. M. Shrimpton^1,*, D. A. Patterson², J. G. Richards³, S. J. Cooke⁴, P. M. Schulte³, S. G. Hinch⁴ and A. P. Farrell^3,5

¹ Ecosystem Science and Management Program, University of Northern British Columbia, Prince George, BC, V2N 4Z9, Canada
² Fisheries and Oceans Canada, Science Branch, Pacific Region, Cooperative Resource Management Institute, School of Resource and Environmental Management, Simon Fraser University, Burnaby, BC, V5A 1S6, Canada
³ Department of Zoology, University of British Columbia, Vancouver, BC, V6T 1Z4, Canada
⁴ Centre for Applied Conservation Research, Department of Forest Sciences, University of British Columbia, Vancouver, BC, V6T 1Z4, Canada
⁵ Faculty of Agricultural Sciences, University of British Columbia, Vancouver, BC, V6T 1Z4, Canada

^* Author for correspondence (e-mail: shrimptm{at}unbc.ca)

Accepted 5 September 2005

We present the first data on changes in ionoregulatory physiology of maturing, migratory adult sockeye salmon Oncorhynchus nerka. Fraser River sockeye were intercepted in the ocean as far away as the Queen Charlotte Islands (850 km from the Fraser River) and during freshwater migration to the spawning grounds; for some populations this was a distance of over 700 km. Sockeye migrating in seawater toward the mouth of the Fraser River and upriver to spawning grounds showed a decline in gill Na⁺,K⁺-ATPase activity. As a result, gill Na⁺,K⁺-ATPase activity of fish arriving at the spawning grounds was significantly lower than values obtained from fish captured before entry into freshwater. Plasma osmolality and chloride levels also showed significant decreases from seawater values during the freshwater migration to spawning areas. Movement from seawater to freshwater increased mRNA expression of a freshwater-specific Na⁺,K⁺-ATPase isoform (1a) while having no effect on the seawater-specific isoform (1b). In addition, gill Na⁺,K⁺-ATPase activity generally increased in active spawners compared with unspawned fish on the spawning grounds and this was associated with a marked increase in Na⁺,K⁺-ATPase 1b mRNA. Increases in gill Na⁺,K⁺-ATPase activities observed in spawners suggests that the fish may be attempting to compensate for the osmotic perturbation associated with the decline in plasma chloride concentration and osmolality.

Key words: sockeye salmon, Oncorhynchus nerka, ionoregulation, migration, salinity, spawning

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