Vulnerability of three fish groups (tilapia, common carp, mullet) to predation by Nile perch Lates niloticus was evaluated. The study was conducted in aquaria and in cages placed in concrete ponds. Common carp Cyprinus curpio was the more vulnerable to predation by Nile perch followed in order by mullet (Mugil cephulus and M. cupito) and Nile tilapia Oreochromis niloricus. Medium-size Nile perch (30–32 cm t.l.) were able to consume tilapia up to 14 cm t.l., while tilapia of 15 cm total length were not eaten. Ratios of 1 : 10 to 1 : 15 between Nile perch and ready-to-spawn females of O. niloticus were found to be adequate to control tilapia reproduction.