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In this study, the effect of water temperature on pathogenesis of Aeromonas hydrophila in freshwater Crayfish Astacus leptodactylus were investigated. In our study, The treatments Crayfish have exposed to A hydrophila with concentration of 3×106 CFUml-1 in high water temperature (25˚C) and normal water temperature(10-15ċ). The untreated control groups in high water temperature (25˚C) and normal water temperature (10-15 ˚C) were disinfected by oxytetracyclin at concentration of 100 ppm for 24 hours. The haemolymph samples were withdrawn for measuring of THC and TPP. For histopathological studie, the Crayfish samples were fixed in Davidson fixative. The results showed that the value of THC in control group1 in comparing with control group2 and two other treatments at 48h after experiment time were significant (p<0.05). Also the difference of THC value between control group 2 with treatment group2 at 144h after experiment time was significant (p<0.05). The finding of TPP value showed that there was significant difference between control group1 and treatment4 in last time after experiment time (336h) (p<0.05). In infected Crayfish to bacteria with high temperature, red and black spots and also wound were observed. The result of histopathology in heptopancreas, gill, heart and digestive tract showed hemocyte aggregation, necrotized tissue, dead cells within pyknosis and karyorrehexis of nucleus and vaculation of hepatopancreas. In treatment group1 and control group1 no pathological changes of heart were observed. In digestive tract no changes were appeared in treatment1 and two others control group, but aggregation of hemocyte with pyknosis of nuclei was revealed in concentration of 3×106 CFUml-1 with high temperature.