The interrelationship of cortisol, gill (Na + K) ATPase, and homeostasis during the Parr-Smolt transformation of Atlantic salmon (Salmo salar L.).
Serum cortisol concentrations were measured in juvenile Atlantic salmon (Salmo salar L.) undergoing the parr-smolt transformation in fresh water, at either 1 year (S1 population) or 2 years (S2 population) after hatching. Serum cortisol levels were generally low (less than 10 ng ml-1), but during smoltification became significantly elevated in both populations. In addition, the S2 population showed a small cortisol peak in the autumn prior to smoltification. Simultaneous measurement of gill (Na + K) ATPase activity and serum cortisol concentrations in S2 salmon juveniles revealed that both features rose during smoltification in fresh water. The rise in gill (Na + K) ATPase activity was independent of cortisol levels, and preceded the rise in cortisol titer by approximately 1 month. After seawater transfer, gill enzyme levels remained high while cortisol titers fell sharply. Serum cortisol levels, but not gill (Na + K) ATPase activities, were progressively reduced by acclimation of smolts to increasing salinities. Linear regression studies indicated that, at any one level of gill (Na + K) ATPase, cortisol titer increased with increasing surface area: volume ratio. Extracellular fluid volume (sodium space) was found to decline with increasing gill (Na + K) ATPase activity, and to increase with serum cortisol titers. These results indicate that high serum cortisol levels represent a secondary response caused by the development of hypoosmoregulatory ability while still resident in fresh water. Cortisol does not appear to directly stimulate gill (Na + K) ATPase activity in Atlantic salmon smolts.
D000818:Animals; D005618:Fresh Water; D005880:Gills / Q000201:enzymology*; D006706:Homeostasis; D006854:Hydrocortisone / Q000097:blood*; D012474:Salmon / Q000033:anatomy & histology / Q000502:physiology*; D012621:Seasons; D012623:Seawater; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*; D014882:Water-Electrolyte Balance
D000254:Sodium-Potassium-Exchanging ATPase; D006854:Hydrocortisone