Abstract: A commercial fish-growing system particularly adapted for use at the head waters of irrigation systems comprises an elongated, level ditch having a cross-section in the form of an inverted trapezoid as a fish-growing raceway. Water for the irrigation system is supplied to an aeration raceway in which the water is subjected to a violent tumbling action as it passes down the aeration raceway. After the water exits the aeration raceway, it enters the fish raceway. At the outlet end of the fish raceway, an underwater spillway slopes upwardly from the bottom of the pool in which it is located to a lip located below the water level in the fish raceway; and a cofferdam is spaced from and is parallel to the sloping spillway surface. The cofferdam also is spaced from the pool bottom a predetermined distance, so that water and solid wastes exiting from the fish raceway flow upwardly from the bottom along the sloping spillway surface to be dumped out over the lip of the spillway.