Monovalent plasma ion regulation in the hypophysectomized Atlantic salmon

Atlantic salmon, Salmo salar, were hypophysectomized by a buccal approach and placed in fresh water directly or after 2 weeks in one-third seawater. Fish transferred directly appeared unable to regulate plasma Na+ and C1- and failed rapidly. Those kept in dilute seawater before transfer had lower Na+ and C1- levels. However, this group had no mortalities and Na+ levels rose significantly within 2 months. No significant effects of hypophysectomy on K+ or hematocrits were noted. Hypophysectomized animals blanched markedly providing a useful indication of a successful operation. It appears that the pituitary is concerned with the retention of C1- and Na+ but that other factors are probably also involved in regulating Na+. A detailed discussion is provided on the management of the anesthetized animal during hypophysectomy.