en تخصصي Special پژوهشي Research <p><strong>Background:</strong> Edifenphos, a kind of organophosphate toxins, is used as agricultural fungicides in rice fields. This study was aimed to investigate the effect of temperature on lethal concentration of exposure to edifenphos on <em>Rutilus</em> <em>frisii</em> <em>kutum</em> (Caspian kutum).</p> <p><strong>Methods:</strong> The experiment was carried out in static condition and based on instructions of OECD within 10 d under controlled water physicochemical factors. Dissolved oxygen was fixed on 7-7.5 ppm, pH: 7 to 7.5 and hardness: 200 ppm. Fish were acclimatized in 70*40*30 cm aquarium for 10 d before the test. Treated aquariums with concentrations of 0.01, 0.05, 2, 4, 8, 16 ppm of edifenphos with one control group (no toxic concentration), were performed. In order to test the effect of temperature on acute toxicity, three ranges of 15&plusmn;1, 20&plusmn;1 and 25&plusmn;1 &ordm;C were treated and L_C1, LC₁₀, LC₃₀, LC₅₀, LC₇₀, LC₉₀and LC₉₉ were calculated for 24, 48, 72 and 96 h. The study was carried out in Laboratory of Aquaculture and Fisheries, University of Tehran in 2016.</p> <p><strong>Results:</strong> LC₅₀ value in 25 &ordm;C was lower than 20 and 15 &ordm;C. LC₅₀ 96h edifenphos for Caspian kutum in 15&plusmn;1, 20&plusmn;1 and 25&plusmn;1 &ordm;C was 3.70, 3.61 and 3.26, respectively.</p> <p><strong>Conclusion:</strong> Higher temperature increase toxicity rate of edifenphos and the toxin had a positive temperature coefficient on Caspian kutum.</p> Caspian kutum, Organophosphorus fungicide, Temperature, Lethal concentration, Edifenphos Caspian Kutum, Edifenphos, Organophosphorus Fungicide, Lethal Concentration, Temperature 39 44 http://ijt.arakmu.ac.ir/browse.php?a_code=A-10-253-2&slc_lang=en&sid=1 Saeid Shahbazi Naserabad saeid.shahbazi@alumni.ut.ac.ir 10031947532846005906 10031947532846005906 Yes MSc of Aquatic Ecology, Young Researchers and Elite Club,Yasooj Branch, Islamic Azad University, Yasooj, Iran. Alireza Mirvaghefi 10031947532846005907 10031947532846005907 No Department of Fisheries, University of Tehran, Karaj, Iran. Ghasem Rashidiyan 10031947532846005908 10031947532846005908 No PhD Candidate of Fisheries Aquaculture, Young Researchers and Elites Club, Science and Research Branch, Islamic Azad University, Tehran, Iran. Narges Rostamian 10031947532846005909 10031947532846005909 No MSc.of Aquatic Ecology, Department of Fisheries, College of Environment Karaj, Karaj, Iran. Hamed Ghafari Farsani 10031947532846005910 10031947532846005910 No PhD Candidate of Aquaculture Young Researchers and Elite Club, Shahrekord Branch, Islamic Azad University, Shahrekord, Iran.