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¹ Çukurova University, Faculty of Science and Letters, Department of Biology 01330, Balcali, Adana, Turkey DOI : 10.4194/1303-2712-v1241_14 Viewed : 3864 - Downloaded : 3273 Anthropogenic activities can increase the salinity of freshwaters. Thus, freshwater fish Oreochromis niloticus were exposed to Cd (1.0 μg/mL) in increased salinities (0, 2, 4 and 8 ppt) for 0, 1, 3, 7 and 14 days. Following single and combine exposures to salinity and Cd, Na⁺/K⁺-ATPase, Mg²⁺-ATPase, Ca2+-ATPase activities were measured in the gill, kidney and intestine. In general, salinity alone exposures increased Na⁺/K⁺-ATPase activity in the gill and intestine while there were fewer alterations in the kidney. Mg²⁺-ATPase activity significantly altered in the intestine and kidney. Ca²⁺-ATPase in the tissues significantly decreased, the kidney showing the most decrease. Salinity+Cd combine exposures decreased Na⁺/K⁺- ATPase activity in 2 ppt medium in the gill while the activity increased at 8 ppt medium. Na⁺/K⁺-ATPase activity in the intestine decreased in relation to salinity increase, though there was no significant decrease in the kidney. Mg²⁺-ATPase and Ca²⁺-ATPase activities showed a declining trend with the increase in salinity. Cd accumulation in the tissues decreased as the salinity of medium increased, though accumulation in the gill increased regardless of salinity increase at the longest exposure period. Results emphasized necessity of measuring fish ATPase activities in evaluation of data from environmental monitoring, as they are highly sensitive to the changes in the aquatic medium. Keywords : ATPase, tilapia, metal, osmoregulation, gill, kidney, intestine