EFFECT OF COLD ACCLIMATION ON ELECTROLYTE DISTRIBUTION IN RAINBOW TROUT (SALMO GAIRDNERII)

Abstract

The effect of adaptation to constant low environmental temperature on water and electrolyte distribution in skeletal muscle and brain has been studied in 2-year-old rainbow trout. Following introduction to 6 °C of trout previously acclimated to 16 °C, measurements were made, at intervals, of plasma Na, K, Cl, Ca, Mg, and phosphate and of brain and muscle Na, K, and Cl. Plasma, muscle, and brain tissue showed a transient but significant drop in water content during the first days of cold exposure. A coincident paradoxical increase in total body weight suggests the possibility of an osmotic withdrawal of body water by the gut contents during this period. Cl space and Cl–K space estimates of muscle extracellular space were not significantly influenced during cold acclimation. Most of the plasma electrolytes measured showed significant transient alterations in concentration.Significant reciprocal changes in brain Na and K concentration were measured shortly after transfer to 6 °C and a large (61%) increase in brain Cl concentration occurred after 3 weeks of cold adaptation.Large, rapid but mostly transient shifts in muscle Na and K occurred. During the first 3 days of cold exposure muscle lost 61% of the Na and 30% of the K present before transfer. This loss is reflected in a rise in plasma Na and K. The possibility that the unusual efflux of intrafiber Na and K together might represent a forced extrusion of positive charge following a temperature-induced intrafiber loss of organic anions or gain of divalent cations is discussed.