p. 191 - 198 THE REPARTITION OF WATER AND Na+ AND K+ IONS IN THE TISSUES OF TROUTS TRANSFERRED FROM FRESH WATER INTO THE SEA WATER Valer Craciun 1), Margareta Craciun 1), Ion Neacsu 1), Adrian Telembici 2), Reveica Ionita 2) 1) Biological Research Center Iassy 2) Romanian Marine Research Institute Constanta Abstract The extra- and intracellular volumes and the distribution of Na+ and K+ ions in the extra- and intracellular compartiments of the muscular, renal and intestinal tissues of trouts were measured at different intervals after the transfer into the sea water. The extra- and intracellular volume and the Na+ content increased, and the K+ content decreased in the first day, than was seen a slight tendency of coming back to the initial values (except the intracel- lular volume), which were reached in the marine fully adapted trouts. In these animals a new hydric and ionic equilibrium was reestablished.