Abstract: A waste-water filtration device for fish cultivation comprises a thin rotatable filter material through which waste water flows from the inside surface to the outside surface, a removing means which comprises a brush on either of the inside or outside surfaces for relatively scraping the inside and outside surfaces of said rotatable filter material, and a drive assembly which comprises a power supply means and a bearing means to drive the rotatable filter material whereby the rotatable filter is cleaned by removing the waste matter which adheres to said filter material.