Copper is an essential trace element, but because of its highly reactive nature can also be toxic to aquatic organisms. Effect of copper is complex on aquatic organisms and it depends on physical and chemical characteristics of water. Water temperature is one of the most important physicochemical variables that affect the overall performance of aquatic communities.The most important indicators of physiological status under stressful conditions are ionic(osmotic) regulators and the body's major electrolytes (sodium and potassium) concentration. In this study, the effects of copper, temperature and combined copper and temperature on osmoregulation ofIsfahan endemic toothcarp ( Aphaniusisfahanensis ) were studied.At the first, the tolerance thresholds of temperature were indicated at high and low temperatures which were 38.5 ± 0.32and 3.4 ± 0.25 °Crespectively.The median lethal concentration (LC 50 ) 96-hour of copper was determined (0.483 mgl -1 ) with confidence interval0.378 to 0.680 mgl -1 .Temperature treatments were based on the 20% tolerance threshold of temperatures at high and low, which were indicated 31.5 and 10.5 ° Crespectively, Also the optimum temperature was determined 21 ° Caccording to primary adaptation temperature.Concentrations of copper treatments were determined as 10% and 25% median lethal concentration (LC 50 ) 96 hours, which were0.0485 and 0.12075 mgl -1 respectively.Experimentwas done at three temperatures (10.5, 21 and 31.5 ° C) and three copper concentrations (0, 0.0485 and 0.12075 mgl -1 ) in 8 treatments and one control group during two weeks.At first, experimentwas run forone week in temperature treatments, then continued in combined copper and temperature treatments for another week.At the end of the experiment, copper accumulation andmoisture content in gill, moisture content, ash and sodium and potassium ion concentrations in musclewere measured. The content of moisture and copper accumulation in gill in all treatments were significantly increased compared to the control group. Furthermore, significant increase in muscle moisture and ash was observed in all treatments toward the control group. But the amount of sodium and potassium in most treatments was significantly reducedcompared to the control group.In conclusion, it can be claimed that the temperature, copper and combined copper andtemperature treatments as the stressorsimpact significantly on this speciesosmoregulation. Keywords: Copper, temperature, toothcarp ( Aphaniusisfahanensis ), ionic(osmotic) regulators, tolerance threshold of temperature, the median lethal concentration (LC 50 ) 96-hourofcopper, osmoregulation
