Densities of 9 tilapia (hybrid Oreochromis mossambicus x O. urolepis hornorum)/m(3) gave the highest production among five densities(1, 3, 6, 9, and 12 fish/m(3)) rested in a pulsed-flow culture system. Culture of fish in irrigation ditches may have great potential for integrating fish farming with irrigated agriculture. Each 1,000 meters of ditch could potentially produce up to 1,400 kg of tilapia during a 112-d growing season.