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The environmental legislation on waste loadings and the public discussion on environmental issues concerning inland aquaculture facilities have become stronger in recent years. An end of the discussion cannot be foreseen. At the same time, the pollution emitted per ton of ¢sh produced has decreased successively over the last 20 years. In this con£ict, this paper provides an overview on: (1) pollutants typical for £ow-through trout aquaculture, (2) their source and potential environmental impacts and (3) strategies to reduce the e¥uent pollution from £owthrough trout farms, a brief description of their function principles and application and, if possible, their economical feasibility. This study aims to identify the actual e¥uent problems of £ow-through trout aquaculture and to o¡er possible solutions by either pollution avoidance or e¥uent treatment. Future trends and research needs on e¥uent treatment are outlined. As the amount of nutrients discharged is typically site and operation speci¢c, farm management is most important for avoidance of e¥uent pollution. Nevertheless, for further production expansion, 'end of pipe' technologies are needed to reach adequate e¥uent qualities. Partial water reuse can improve ef-£uent discharge. Physical, chemical and biological technologies can be used to treat trout farm e¥uents. Today, the commonly used physical (mechanical) treatments in trout aquaculture like screening and sedimentation only remove suspended solids, containing up to 7^32% of total nitrogen and 30^84% of total phosphorus. The remaining soluble nutrients can only be removed by either the application of che-micals or biological e¥uent treatments. The possible applications of biological technologies are manifold, but practical and upscale experience is lacking.

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-In the context of the European Water Framework Directive, the in-and outflow water quality from 13 German trout farms, rearing mainly rainbow trout (Oncorhynchus mykiss) and using inflow rates between 0.03-0.80 m 3 s −1 , were monitored for point-source pollution. The farms had a significant effect on the effluent quality and macro-invertebrate fauna in adjacent streams (saprobic index based on species assemblage and abundance was 1.56-2.10 upstream of the farms but increased to 2.06-2.37 downstream of the farms). Inflow water quality, type of rearing unit, feeding intensity (amount of feed input in relation to water resources) and effluent treatment method could be used to predict effluent quality by 50 to 88% for most water characteristics. Based on these results, different effluent treatment options were monitored for their treatment performance. Concrete sedimentation basins 11 m × 7 m × 1.2 m and 5.5 m × 3.3 m × 1.5 m (L × W × H), respectively, used for total farm effluent had little or no treatment effects. The micro-screen examined was relatively effective on particulate water components, measured as total phosphorous (TP), biochemical oxygen demand (BOD 5 ), chemical oxygen demand (COD) and total suspended solids (TSS), resulting in treatment efficiencies of 29-53%, which is less than expected from data in the literature. The constructed wetland examined showed the highest treatment efficiency: more than 35% for TP, COD, BOD 5 , TSS and total ammonia nitrogen (TAN). From these results and data from the literature, treatment strategies for trout farm effluents can be developed, depending on the rearing system and production intensity. Key words:Aquaculture ecological impact / Trout farming / Effluent quality / Effluent treatment / Sedimentation basins / Constructed wetlands Résumé -Impact de l'aquaculture des truites sur la qualité de l'eau et les traitements des rejets aquacoles. Dans le contexte de la directive cadre européenne sur l'eau, la qualité de l'eau, en entrée et en sortie, a été suivie sur 13 piscicultures allemandes de truites, élevant principalement des truites arc-en-ciel (Oncorhynchus mykiss) et utilisant des débits d'entrée de 0,03 à 0,80 m 3 s −1 , pour évaluer les sources de pollution. Les piscicultures ont un effet significatif sur la qualité des effluents et la faune de macro-invertébrés des rivières voisines (l'index saprobique, basé sur l'assemblage et l'abondance des espèces, est de 1,56 à 2,10 en amont des piscicultures mais augmente en aval : 2,06 à 2,37). La qualité des entrées d'eau, le type d'unité d'élevage, l'intensité de l'alimentation (quantité de nourriture fournie en relation avec les ressources en eau) et la méthode de traitement des effluents peuvent être utilisés pour prédire leur qualité de 50 à 88 % pour la plupart des caractéristiques de l'eau. D'après ces résultats, les différentes options de traitement sont contrôlées pour leur performance. Des bassins de sédimentation en béton 11 m × 7 m × 1,2 m et 5,5 m × 3,3 m × 1,5 m (longueur × largeur × profondeur...