Effects of hypophysectomy on osmoregulation in the euryhaline flounder, Platichthys flesus (L.), in sea water and in fresh water

Abstract

1. 1. The effects of hypophysectomy on osmoregulation in the euryhaline flounder, Platichihys flesus (L.), were investigated. 2. 2. In sea water blood Na +, K +, Ca 2+ and Mg 2+ levels were unaltered; Cl − and osmolality were reduced slightly. Urine Na +, K +, Mg 2+ and flow were unaffected; Ca 2+ was decreased. Secretion of a hyperosmotic urine in intact fish was associated with stress; marked reductions in urine Cl − and osmolality occurred in ablated fish. 3. 3. Impaired fresh-water tolerance was due to marked reductions in blood osmolality, Na + and Cl~; K + and Ca 2+ were unaffected but Mg 2+ declined. Urine Na +, Mg 2+ and Cl − were unaltered; K + and Ca 2+ were increased. 4. 4. High Na + and Cl − losses were extrarenal in origin. These defects probably arose from a prolactin deficiency, though delayed hormone treatment did not increase blood Na +. 5. 5. These results are discussed in relation to information on other teleosts.