Effects of fish farm effluents on the periphyton of an Andean stream

Abstract

In this study we analyse the structure and composition of the periphyton, upstream and downstream of a fish farm located at an Andean stream. The effluents discharges large quantities of phosphorus and organic matter from the feed remnants and the faeces. The input of organic matter caused a reduction in algal biomass and a change in the relative abundance of some species. The ratio between chlorophyll a and total organic matter concentrations indicated that the periphyton consisted of a high photosynthetic fraction at upstream sites, while downstream heterotrophic conditions were favoured. The community, which was composed mainly of diatoms, was dominated by Achnanthes minutissima at every site, except at the mouth of an effluent channel of the fish farm, where Nitzschia supralitorea dominated. When there are high organic matter inputs, the prostrate motile form acquires advantages over the rosette, adnate and filamentous forms, with a consequent change in community structure.