A description is given of the physical f,acilities in which mass cultures of penaeids have been reared from eggs to postlarvae. The metal chelator EDTA was added to the water in which the shrimp were grown. Larvae of Penaeus aztecus developed more rapidly, at 30° C than at lower temperatures. Salinity varied from 20.5% to 36.0% during rearing trials in which P. aztecus Iarvae were reared to postIarvae. Addition of mixed, algal cultures ,as food g,ave better survival than additions of their individual components. EDTA was used as an additive to filtered sea water to grow a diatom, Skeletonema sp., in mass culture, as food for larval shrimp.