Influence of water temperature on gill sodium, potassium-stimulated ATPase activity in juvenile coho salmon (Oncorhynchus kisutch)

1. Gill sodium, potassium-stimulated ATPase activity was determined from December to July in gills of yearling coho salmon (Oncorhynchus kisutch) maintained at four temperatures, 6, 10, 15 and 20°C.

2. Compared to fish held at 6°C, elevation in ATPase activity and the associated parr-smolt transformation were accelerated in fish at 10 and 15°C whereas animals at 20°C experienced at best only a transitory elevation in activity.

3. Fish transferred from one temperature to another developed ATPase activities characteristic of fish residing at temperatures to which they were transferred.

4. Cold water (6°C) tended to preserve the elevated ATPase activity while higher temperatures (10 and 15°C) caused decreases after an initial accelerated increase.