Adaptive Changes in Ion and Water Transport Mechanism in the Eel Intestine

Abstract

Living in aquatic environments with a wide range of salt concentration, teleost fishes are known to maintain their osmotic pressure and electrolyte concentrations at levels largely independent of the salinity of their environment. Freshwater teleosts, which are hyperosmotic to the environment, tend to gain water by osmosis. They drink little water and the kidneys have the task of removing excess water. In contrast, seawater teleosts constantly face a pressing problem in water conservation because of their hypertonic environment. In order to replace the osmotic loss of water, they drink surrounding sea water and absorb water with monovalent ions from the intestine. The excess sodium and chloride ions are extruded by the gill, leaving osmotically free water in the body1–4.