Journal of Aquatic Ecology

 One of the problems for rivers and streams in Iran is related to dispersal of the waste effluents from trout farms. The aim of this study was to assess the effects of trout farm effluents on Zarin-Gol stream using macrobenthos communities, Helsenhoff, BMWP and ASPT indices. Sampling of macroinvertebrate was performed in six stations (entrance of fish farm, discharge and 500 far from fish farm) in three replicates using surber sampler in winter and spring, 2016. The number of total abundance of macroinvertebrate were counted 2179 belonging to 8 order, 30 families and 15 genus. The results showed that the trout farm effluents had significant effects on nitrite and dissolved oxygen. The highest value of BMWP and ASPT was obtained in station 1 in winter season, while the lowest value was obtained in stations 2 and 5 in spring season, considered asthe middle class in terms of water quality. The maximum value of Helsenhoff index was observed in station 2 (5.31) in winter season, considered as relatively weak class in terms of water quality. The result of indices showed a decrease in macrobenthos sensitive to pollution, and stations located after trout farms were more polluted than those located before farms, indicating lower water quality.