effect of different salinity on ions, osmolarity, water concentration of body tissue, gill chloride cells and mortality percentage of juveniles of caspian roach (rutilus frisii kutum kamensky 1901)

changes of ions (na+, cr, k+), osmolarity and water concentration of body tissue, size and number of gill chloride cells as well as mortality percentage of the juveniles caspian roaches in weight groups of0.2, 0.5 & 1g water satiny stress were studied. the salinities tested  were 0 (fesh water), 7, 12.5 & 16g/lit and the assessments were completed 0, 12, 24, 48 & 72 hours after exposure. results showed that ions and osmolarity of juveniles  weighting 0.2 & 0.5g in salinities of 0 up to 12.5g/lit increased significantly  during the first  12 hours (p&apos;<0.05).  these values then  showed downwara trend to the values recorded for fresh water. water concentration of body tissue reached the minimum mean value in 12 hours (p<0.05) in salinity of 12.5 g/lit and then showed upward trend to the value obtained for freshwater. ions and osmolarity of body tissue of the juveniles  mcreased and water concentration of body  tissue  decreased  significant  after  the  first  12 hours  of  transferring  into  salinity  of  16g/lit (p<0.05). weight changes in juveniles  of 1g in salinities of 0 up to 16g/lit was similar to juveniles  of 0.2 & 0.5g in salinities of 0 up to 12.5gllit and the maximum mean vafues of ions and osmolarity and the minimum value of water concentration body tissue in 16g/lit salinity in hour 12 (p<0.05). size and number of gill chloride cells  of juveniles weighting 0.2 & 0.5g in salinities of 0 up to 12.5g/lit increased significantly during the first 12 hours of exposure (p<0.05) and reached the maximum mean values in 12.5g/lit salinity 12 & 24 hours after exposure, respectively (p<0.05) and showed invisible changes up to the end of the test. size and number of choride cells of the juveniles increased after the first 12 hours of transferring into salinity of 16g/lit (p<0.05). changes of the indices in juveniles weighting 1gin salinities of 0 up to 16g/lit was similar to juveniles of 0.2 & 0.5g kept in salinities of 0 up to 12.5gtlit and the maximum values was in 12 and 24 hours after exposure, respectively (p<0.05). ions and osmolarity of body tissue and size and number of chloride cells increased significantly with increase of salinity and wetght and water salinity and water concentration of body tissue decreased significantly with mcrease in water salinity and increased in fish weight (p<0.05). juveniles weighting 0.2 up to 1g showed no mortality in salimties of 0 & 7g/lit during tfie test. mortality of the juveniles weighting 0.2, 0.5 and 1g/1it increased during the first f2 hours and became constant to the end of the test. mortality of juventies weighting 0.2 & 0.5g in salinity of 16gllit was similar to that of the juveniles weighting 0.2 & 0.5f in salimty of 12.5g/lit. mortality of the juveniles increased significantly with increase of salinity and decreased with increase of weight (p<0.05).