VARIATIONS IN THE SODIUM AND POTASSIUM CONTENT OF THE MUSCLE TISSUE OF PACIFIC SALMON WITH PARTICULAR REFERENCE TO MIGRATION

Abstract

Further confirmation was obtained of the observation made previously that the Na+ and K+ levels of the muscle tissue of spring salmon (Oncorhynchus tschawytscha) on the Pacific coast appear to vary with the size of the fish and, in the case of small fish, with the season of the year. Small fish (3 to 5 lb) caught in regions of relatively constant salinity had higher Na+ and lower K+ concentrations in the spring and summer than in fall and winter. Under the same conditions the levels of Na+ and K+ in the flesh of larger fish (9 to 10 lb) did not vary.When spring salmon were sampled along the route of their spawning migration up the Fraser River it was found that at the mouth of the river the Na+ level was less than in fish at sea. Further up the river, Na+ had dropped to less than one-half of the value at sea. At the spawning grounds in three groups out of four examined, Na+ rose again to levels the same as or above those prevailing at sea. In general, a drop in Na+ was accompanied by a rise in K+ and vice versa, though at the spawning ground the drop in K+ considerably exceeded the rise in Na+.In the case of sockeye salmon (Oncorhynchus nerka) heading up river, a lowered Na+ and elevated K+ occurred in the muscle tissue of the fish while they were still in salt water. After the fish had entered fresh water the ion levels were restored and maintained at levels similar to those normally prevailing at sea. At or near the spawning ground a marked rise in Na+ as well as a drop in K+ occurred. Evidence was obtained that this change occurred first in the male of the species.The flesh of juvenile coho salmon (Oncorhynchus kisutch) migrating to the sea was found to contain less Na+ and more K+ than mature fish of the same species caught at sea. Young sockeye in fresh water, however, contained about the same levels of Na+ and K+ as the mature fish at sea.