Electrolyte changes associated with transfer of the steelhead trout (Salmo gairdneri) into seawater

The purpose of the investigation was to elucidate the mechanisms enabling the survival of euryhaline fish in salt water. Steelhead trout (Salmo gairdneri) were transferred to 60% seawater and serial measurements made of the serum and muscle sodium and potassium content and of the tissue water during a ten day period after transfer. The initial 24 hours in seawater were characterized by a dehydration of the tissues and a great increase in the body electrolytes. This was followed by a regulatory phase which represented the mobilization of active transport mechanisms in the muscles and gill tissues, enabling the excretion of the dominant extracellular cation, sodium. The regulation of potassium, the main intracellular cation, was assigned to the kidney. The regulation of tissue potassium and water appeared to be dependant on the regulation of sodium. After 110 hours in seawater the regulatory processes had returned the animal to a new equilibrium which was characterized by: l) serum cations only 6% higher than fresh water controls, 2) muscle potassium 15% higher than fresh water controls, and 3) a lower tissue water content than the fresh water controls. The control of this osmoregulatory adaptation to a hypertonic environment is discussed and possible hormonal action considered.Science, Faculty ofZoology, Department ofGraduat