PLASMA THYROXINE AND GILL NA+-K+ ATPASE CHANGES DURING SEAWATER ACCLIMATION OF COHO SALMON, ONCHORYNCHUS-KISUTCH

1. 1. Plasma thyroxine (T-4) and gill sodium-potassium activated adenosinetriphosphatase (Na+-K+ ATPase) were measured by radioimmunoassay and colorimetric enzyme assay in yearling coho salmon, Onchorynchus kisutch, smolts. Gill and plasma samples were collected from fish in fresh water and then on a daily basis for 8 days following transfer to seawater net pens. 2. 2. Plasma T-4 levels fluctuated in a complex pattern with transient peaks at 24 hr and then again on the fourth or fifth day. 3. 3. Gill ATPase activity remained at freshwater levels until the fifth day in seawater, then increased and remained elevated. 4. 4. These correlative data suggest possible T-4 involvement in the adaptation of coho salmon to seawater. © 1979.