Cortisol stimulates hypo‐osmoregulatory ability in Atlantic salmon, Salmo salar L.

Abstract

Hypo-osmoregulatory ability in juvenile Atlantic salmon, Sulrno salur L., was improved by cortisol treatment. Implantation of a vegetable shortening pellet containing cortisol (50 mg kg-') resulted in elevated plasma cortisol titres. Maximum cortisol levels (160-170 ng ml-') were observed at days 6 and 12 after the implantation and dropped significantly by day 55. Cortisolimplanted fish in fresh water developed a twofold increase in gill Na+/K+-ATPase activity at days 6 and 12, and a threefold increase by day 55. Intestinal mucosa Na+/K+-ATPase activity was not affected by cortisol. Cortisol-implanted fish exposed to 28 ppt sea water for 48 h tended to show an improved ability to regulate their plasma osmolarity and reduce their ionic load. The osmoregulatory ability attained at days 12 and 55 was further evaluated by exposing fish to 37 ppt sea water for 96 h. While all the control fish died relatively early in these tests, cortisol-implanted fish showed a clear reduction in their mortality rate. These results indicate that cortisol can induce biochemical and organismal changes during winter months that typify preadaptive events normally occurring in the spring.

Regulation of the glucocorticoid receptor mRNA levels in the gills of Atlantic salmon (Salmo salar) during smoltification

“…In vitro studies established a direct effect of Cortisol on Na + /K + ATPase in coho salmon gill tissue (Mc CORMICK and BERN, 1989). In Atlantic salmon, Cortisol implants have been reported in some studies to stimulate hypo-osmoregulatory ability with a two to three fold increase in gill Na + /K + ATPase activity (BISBAL and SPECKER, 1991) whereas in other studies, Cortisol treatments applied to presmolts had no effect on their seawater adaptability (BOEUF et al, 1994). More recently, a synergistic effect of GH and Cortisol was shown for salinity tolerance of Atlantic salmon (Mc CORMICK, 1996).…”

Expression of insulin-like growth factor I gene in osmoregulatory organs during seawater adaptation of the salmonid fish: possible mode of osmoregulatory action of growth hormone.

“…Cortisol has previously been shown to be important in salmonid seawater adaptation by stimulation of gill Na+/K+-ATPase activity and chloride cell differentiation (11,44,50,51). Although relatively little is known of the functional relationship between GH and cortisol, GH enhances the in vitro response of coho salmon interrenal to adrenocorticotropin, increasing cortisol production (52).…”

The influence of salinity and prey salt content on growth and intestinal Na+/K+-ATPase activity of juvenile bluegill,Lepomis macrochirus

“…1989) . Although little is known about the amount and rate of intestinal salt absorption in freshwater fishes, the Na+/K+-ATPase pump located on the basolateral membrane of the intestinal epithelium helps balance the osmotic gradient between the blood and the lumenal fluids (Bisbal & Specker 1991, Loretz & Fourtner 1991, Trischitta et al . 1992a .…”