The effect of Rainbow trout farms effluents on benthic macro-invertebrates of Marber River in Semirom

The effect of Rainbow trout farms effluents on benthic macro-invertebrates of Marber River in Semirom city was investigated in spring and summer of 2013. Sampling from benthic macro-invertebrates was done monthly using Surber sampler (mouth area of 30.5 * 30.5 cm with a 500 mesh net) at entrance, discharge and far from three fish farms. In addition to measuring physical and chemical parameters of water, a number of 5326 samples from benthic macro-invertebrates were identified totally, which belonged to 34 genus, 22 families and 8 orders. Indices of EPT richness and EPT/Chir were lower at stations immediately located after the farms in compare to the upstream stations. These indices were improved by getting far from the farms. Hilsenhoff family biotic index categorized the quality of water in the range of fair to excellent. Based on the results, Marber River in Semirom has got the ability of self-purification and at the distance of two kilometers from trout farms, its water quality has been improved.