acute toxicity and behavioral changes associated with diazinon in rutilus rutilus caspicus and hypophthalmicthys molitrix

background: diazinon is an organophosphorous pesticide which widely found in municipal, agricultural, and urban storm water discharges. the present study was conducted to achieve lethal concentration (lc50) and behavioral changes of rutilus rutilus caspius and hypophthal-micthys molitrix after exposure to lethal concentration of diazinon. methods: the experiment was carried out in static conditions, based on instructions of oecd in 4 days under controlled water physicochemical conditions with ph of 7.2±0.2, oxygen of 7±0.3 mg/l, total hardness of 180 mg caco3 and temperature of 24±1 c°. all fishes were accli-matized in 400 l aquaria for 10 days. treated aquaria had concentrations of 0.5, 1, 2, 4, 8, 10, 20, 40, 60, and 80 ppm of diazinon for h. molitrix, and 1, 2, 4, 8, 10, and 20 for r. rutilus caspi-cus, while there was no toxic concentration for the control group. lc1, lc10, lc30, lc50, lc70, lc90, and lc99 were calculated for 24, 48, 72, and 96 hours. results: lc50 96h diazinon values were 3.93 and 1.71 ppm for h. molitrix and r. rutilus caspi-cus, respectively. clinical observation revealed that the poisoned fishes suffered from nerve paralysis syndrome. the fishes exhibited irregular, erratic, and darting swimming movements, severe aching, and collapse to the bottom of the aquarium. conclusion: these findings suggest that diazinon has medium toxicity at low concentrations for thede two species and causes morbidities.