en Ecology Ecology پژوهشي Orginal research papers <p dir="ltr" style="text-align: justify;">In this study the distribution and accumulation of diazinon, malathion and azinfos methyl in mullet fish <em>Liza aurata</em>, caspian white fish <em>Rutilus</em> <em>frissi kutum</em> and common carp fish<em> Cyprinus carpio</em> from five estuaries along the Caspian Sea was investigated. Also, the effect of pesticides concentration on the acetylcholinesterase enzyme (AChE) in fish species was studies. Pesticides concentration varied with fish species, sampling station and toxin type. The results indicate that the pesticides concentration varied from 0.01 to 0.16 mg/kg for diazinon, 0.01 to 0.15 mg/kg for malathion and 0.05 to 0.36 mg/kg for azinfos methyl in three fish species. There was significant difference between different toxin concentrations in fish species, (P < 0.05), and the order of toxic concentrations was as follows: azinfos methyl > diazinon > malathion. There was significant difference in toxin concentrations between three fish species, and the highest toxins concentrations were absorbed in detritivores fish (<em>L. aurata</em>), followed by herbivorous fish (<em>C. carpio</em>) and carnivore fish (<em>R. kutum</em>). The results confirmed that toxins bioaccumulation in fish species is strongly controlled by habitat and feeding habits.</p> Diazinon, Malathion, Azinfos methyl, Acetylcholinesterase, Caspian Sea 3050 3062 http://jifro.ir/browse.php?a_code=A-10-2114-1&slc_lang=en&sid=1 R. Golshani golshani.eme88@yahoo.com 100319475328460038356 100319475328460038356 Yes ISLAMIC Azad University,Science and Research A. Mashinchian Moradi Ali2m@yahoo.com 100319475328460038357 100319475328460038357 No ISLAMIC Azad University,Science and Research R. Mosavi Nodoshan mousavi.nadushan@gmail.com 100319475328460038358 100319475328460038358 No ISLAMIC Azad University,Science and Research S.M. Fatemi reza_fatemi@hotmail.com 100319475328460038359 100319475328460038359 No ISLAMIC Azad University,Science and Research P. Ghavam Mostafavi gh.mostafavi@gmail.com 100319475328460038360 100319475328460038360 No ISLAMIC Azad University,Science and Research