Abstract: A device for removal of sediment particles from the water in a cultivating tank for aquatic organisms. The cultivating tank has a cylindrical outlet connected to an outlet tube located on the vertical axis of symmetry of the cultivating tank. A plate is spacedly positioned above the upper edge of an annular chamber formed at the bottom of the tank around the outlet to form a slotted opening into the annular chamber. The annular chamber has a separate outlet formed in or near the bottom for carrying away particles accumulated within the chamber. The portion of the cylindrical outlet near the upper area of the chamber includes a plurality of orifices arranged to collect and withdraw relatively clear water. In an other embodiment, the cultivating tank having a flat bottom can have a cone shaped inwardly tapering section surrounding the cylindrical outlet which forms the annular chamber.