Résumé: The current onshore aquaculture trend is to develop large scale production of diversified fingerlings and very large units for fish ongrowing. This requires an industrial type of approach including quality assurance and minimization of failures in addition to management of bio-technical and economic aspects. Therefore, all the key biological mechanisms involved in Recirculating Aquaculture Systems (RAS) need to be better understood, especially those determining the development of bacterial populations and their interactions with fish. This review presents new knowledge on bacterial community compositions in various parts of RAS and on bacterial-fish interactions in RAS, which constitute essential tools for system management. (C) 2012 Elsevier B.V. All rights reserved.