During the spawning period, fishes of the familes Mugilidae and Centropomidae concentrate on the river mouths or brackishwater lagoons. Those species are reared in fish-ponds ("viveiros") in northeastern Brazil, mainly at Pernambuco State. Presently, polyculture trials are made with those species, together with three others of the family Gerridae, with or without artificial feeding or fertilization. The yields are very high per ha /year. A review of the biology of those species, together with the hydrological conditions of the fish-ponds, are presented. The author recommends that similar fish-ponds should be built in other northeastern regions as well as in the south, and the obtention of fry through hypophysation method (now used in Israel and Taiwan for Mugilidae), replacing the present method of simply catching youngs measuring 10 to 15 cm total length and putting them in those fish-ponds. In this way we would contribute to a high and quick production of animal protein, necessary to a great part of Brazilian population.