The intensification of rearing techniques has enormously increased the organic pollution of land based fish farming effluents, representing a problem of increasing concern. During the last years some European private companies have decided to set up a new system for the treatment of fish farm sewage. After preliminary tests, mechanical gravitary devices have been found the most adapted equipment to reduce suspended solids in the effluent, with filtration efficiency up to 80 per cent. Future steps of the work will be the sludge conditioning and disposal to achieve the complete integration of the system. This project is co-financed by the European Commission.