assessment of fish farm effluents on macroinvertebrates based on biological indices in tajan river (north iran)

impacts of effluent from fish farming activities on fluvial ecosystems lead to deterioration of water quality and changes in the macroinvertebrates assemblage. in this study, the influence of fish farm effluents on water quality and macroinvertebrates communities of tajan river was investigated to evaluate the suitability of macroinvertebrates based on biological metrics and indices. benthic macroinvertebrate communities were analyzed seasonally for a period of one year . five sampling stations were selected along the study reach of 50 km. station 1(s1) which is located upstream from the fish farm, was used as the reference site. station s2 and s3 were located downstream from the fish farm outlet; s4 and s5 were further downstream. in order to assess the changes in diversity and richness in relation to water quality, two major groups of sites based on similarity between macroinvertebrate communities identified by cluster analysis. diversity of macroinvertebrates, ept richness and ept/chir indices significantly decreased toward downstream stations except for station s4. conversely, values of hfbi and jacard index significantly increased in the downstream stations. the present study revealed significant differences in water quality parameters between the stations located above and below the fish farms. owing to the relatively high diversity of benthic macroinvertebrates inhabiting rivers, use of macroinvertebrate based biological indices is recommended for assessment of water quality and pollution in fluvial systems.