en aquaculture aquaculture پژوهشي Orginal research papers In this study, the impact of cage culture of rainbow trout (<em>Oncorhynchus mykiss </em>Walbaum), on benthic communities using biological indicators located along the coastal areas of the South Caspian Sea (Nashtarud region, Mazandaran Province, Iran) was investigated. Monthly samplings from 4 stations were carried out from January 2016 to May 2016. The physical and chemical characteristics of water were measured on a monthly basis. Sediment samples were taken using Ekman Grab. The ecological indicators such as Shannon&ndash;Wiener index of diversity, H, Simpson, S, and Margalef, R, was routinely used. The biomass-dominant faunal groups were Bivalve (146.16 g m^-2<span dir="RTL">(</span>, Crustacea (24.5 g m^-2) and Polychaeta (10.5 g m^-2).The greatest variety of benthos was found under the cage and the lowest range was found150-300 m around the cage that was significantly different (<em>p</em><0.05). Results of current study showed that, the percentage of sand was greater than that of silt and clay throughout the experimental period. Sediment organic matter (OM%) reached extremely high concentrations beneath the control (<em>p</em><0.05), when compared surrounding area<strong>.</strong> A positive correlation coefficient was found betwee<a name="_Hlk477399177">the Shannon&ndash;Wiener diversity</a> index (H&#39;), and biomass of benthic organisms (p=0.001; r=0.684). According to results of species diversity, and amount of organic matter in the cage area, indicated that specific richness levels were in bad ecological statues.<span dir="RTL"></span><br> &nbsp; Cage culture, Benthic, Oncorhynchus mykiss, Caspian Sea, Iran 2142 2158 http://jifro.ir/browse.php?a_code=A-10-2517-1&slc_lang=en&sid=1 K. Haddadi Moghaddam khkhmoghadam@gmail.com 100319475328460035648 100319475328460035648 No Department of Fisheries, Faculty of Agriculture and Natural Resources, Science and Research Branch, Islamic Azad University, Tehran, Iran M. Soltani msoltani@ut.ac.ir 100319475328460035649 100319475328460035649 Yes Department of Aquatic Animal Health, Faculty of Veterinary Medicine, University of Tehran, Tehran, Iran A. Kamali KAMALI.ABOLGHASEME@gmail.com 100319475328460035650 100319475328460035650 No Department of Fisheries, Faculty of Agriculture and Natural Resources, Science and Research Branch, Islamic Azad University, Tehran, Iran H.A. Abdolhay hossein_abdolhay@yahoo.com 100319475328460035651 100319475328460035651 No ranian Fisheries Science Research Institute,Agricultural Research,Education and Extension Organization,Tehran, Iran