Cichlid fish from the genus Tilapia nilotica (Hasselquist, 1757) (= Sarotherodon niloticus Linnaeus, 1758) could hinder the increase of four Biomphalaria glabrata (Say, 1818) populations of 20 specimens (14-16mm diameter) kept in glass aquaria containing 28 liters of fresh water, during five weeks, in the laboratory. In aquarium nº 1, was introduced one alevin 55mm long (not computed to the caudal fin); in nº 2, one 63mm; in nº 3, two alevins: 40 and 46mm; and, finally, in aquarium nº 4, three specimens with 38, 39 and 42mm, respectively. The fish ate the planorbid spawnings laid on the aquarium walls - thus hindering the eclosion of the snail's eggs and therefore, the consequent increase of the four mollusc populations under experiment. With the removal of the alevins, it was observed that the planorbid populations increased in the next five weeks. There is a necessity for field investigations to evaluate the predatory action of cichlid fish in natural conditions.