Endocrine control of Na-K-ATPase and seawater adaptation in Anguilla rostrata

Abstract

Cortisol induces a rise in the specific activity of Na-K-ATPase in gill filaments and intestinal mucosa of freshwater eels ( Anguilla rostrata), resembling the changes produced by adaptation to seawater. The ventral surface of freshwater eels injected with 400 μg of cortisol/100 g/day for more than 7–10 days loses its yellow coloration and turns silver, reminiscent of the silver hue of eels spontaneously migrating to the sea. Freshwater eels prepared by 10 days of cortisol injections withstand sudden transfer to full-strength seawater without preliminary residence in 50% seawater, and their plasma chloride does not rise as high as that of control eels abruptly transferred to 100% seawater. The data indicate that cortisol induces a series of changes in freshwater eels, including a rise in Na-K-ATPase of gill and intestine, that successfully prepares these euryhaline teleosts to combat the osmotic stress of migration to seawater.