The Kinetics of Peripheral Exchanges of Water and Electrolytes in the Silver Eel (angujlla Anguilla L.) in Fresh Water and in Sea Water

The recent articles of Maetz (1971), Lahlou (1970), Mayer (1970) and Motais (1970) have synthesized the present knowledge about the functioning of the peripheral outwardly exchanging organs of osmoregulation in teleosts, namely the gills, alimentary tract and kidneys. The silver eel is very good biological material because of its high degree of euryhalinity, its ability to withstand starvation for a long time and its great physical resistance. It can therefore survive numerous and varied surgical operations very well. However, the numerous studies on the eel have essentially been concerned with sodium exchanges and very little with chloride exchanges. In addition, in the fresh water eel, which is unable to absorb external chlorides, the chloride losses recorded for only one of the peripheral organs would be sufficient to bring about the total chloride depletion of the animal within a few months, whereas the starving silver eel can easily survive for more than a year. It has often been emphasized that water and electrolyte exchanges in the eel are increased by physiological shock, such as the effect of experimental handling on diuresis (Chester Jones, Chan & Rankin, 1969) or on ion exchanges (Mayer & Maetz, 1967), the effect of temperature on chloride excretion (Fontaine & Callamand, 1940), on diuresis and on the drinking rate (Gaitskell & Chester Jones, 1971). These observations underline the absolute necessity of creating non-stressful experimental conditions and of checking that they are physiologically innocuous by long-term experiments. We therefore perfected new experimental techniques adapted to long periods of experimentation before studying water and chloride exchanges in the silver eel. These techniques will later be used to study, in good conditions, the regulatory processes which play a part in the eel's adaptation to sea-water. For the present, they have shown us that the non-stressed eel is, given our present knowledge, the teleost most isolated from the surrounding medium.