Abstract: A water recycling and filtering system for use in a fish rearing module is disclosed. The system includes a buoyant filter bed which is located beneath the fish rearing volume, horizontally disposed top and bottom screens for containing the buoyant filter bed, a water collector grid network for withdrawing the filtered water, a sludge scraper device for removing settled solids and sludge from the bottom screen and floor of the module, and; a wash-flight device for returning the filtered water under pressure to the module and washing the buoyant filter bed when needed. This construction allows the filter bed to be repeatedly and indefinitely rejuvenated without removing it from the pond and without requiring a large flow rate. Each module has its own isolated reuse-rearing unit and associated control and pumping equipment unit. Only one module at a time is vulnerable to a failure in the filtering or pumping performance.

Abstract: A biological filter system has a bed of buoyant granules a portion of which xtends above the surface of the fluid. The bed is disposed above the effluent outlet. Distubutor and receiving means are provided by which the filter can be backwashed.