Characteristics of effluents from trout farms and their impact on water quality and benthic algal assemblages of the receiving stream.

In this study, characteristics of effluents from three flow-through rainbow trout farms in Turkey and their impact on water quality and epilithic algal communities of the receiving stream were investigated. Water samples were taken monthly from both inlets and outlets of three fish farms, while both water and epilithic algae samples were collected from two stations (upstream and downstream) in the stream. A significant increase from inlets to outlets was observed for chemical oxygen demand (COD), soluble reactive phosphorus (SRP), total suspended solids (TSS), NH-N and total phosphorus (TP) (p < 0.05) due to no effluent treatment processes and high FCR at the fish farms. The daily average total nitrogen (TN) and TP fluxes of the fish farms predicted with the nutritional method were found close to those measured with the hydrological method. Although there were significant increases in COD, TSS, NH-N, TN, NO-N, NO-N, TP and SRP concentrations at the downstream station compared to the upstream station of the receiving stream (p < 0.05), water quality of the downstream station remained in Class I in terms of examined parameters. Trophic Diatomic Index and Biological Diatom Index values indicated that the upstream station had a better water quality than the downstream station. Also, filamentous algae such as Cladophora glomerata, Ulothrix zonata and Stigeoclonium lubricum were observed at the downstream station. In view of the above findings, several suggestions were put forward to protect the water quality of the receiving stream.