Gill (Na+ +K+)-ATPase involvement and regulation during salmonid adaptation to salt water.

1. The involvement of gill (Na+ +K+)-ATPase in salmonid adaptation to salt water (SW) is discussed. 2. Gill (Na+ +K+)-ATPase increase during SW adaptation is mainly related to the increased number and complexity of chloride cells deputed to salt extrusion. 3. The temporal relationships between serum peaks of thyroid hormones, cortisol, growth hormone, prolactin and gill (Na+ +K+)-ATPase rise during salmonid smoltification, suggest a hormonal involvement in the enzyme stimulation and thus in the acquirement of SW tolerance. 4. Literature on gill (Na+ +K+)-ATPase response to hormonal treatment is reviewed. The effects produced on gill (Na+ +K+)-ATPase and chloride cells by exogenous hormones point out a complex inter-relationship between the hormones considered. The mechanisms involved in hormonal regulation of the enzyme remain a matter of debate.