This study examined the effect of probiotic lactic acid bacteria (LAB) and yeast on growth and survival of tilapias, Oreochromis niloticus and Oreochromis sp. LAB and yeast were included in the diet. Microorganisms were identified at molecular level. The first bioassay (120 days, weight = 0.18 ± 0.03 g) was done with Oreochromis sp. with a control group, and animals fed with the probiotics (5 × 104, 1 × 106 and 1 × 107 CFU/g feed). The second bioassay lasted for 92 days with juveniles of Oreochromis sp. (weight 4.09 ± 0.99 g) and O. niloticus (weight 6.12 ± 0.86 g) and consisted of a control group and animals fed with probiotics (5 × 104 CFU/g) daily, every 10 days, and during the first 10 days only. LAB belonged to Pediococcus parvulus and yeast to Candida parapsilosis. In the first bioassay, no significant differences were found in survival and weight of Oreochromis sp. In the second bioassay, no significant differences were found in survival, but, in growth, fish fed with probiotics every 10 days (O. niloticus) and fish fed with probiotics daily and every 10 days (Oreochromis sp.) grew significantly better than the control group. The results indicated that LAB and yeast can be used as a feed additive every 10 days to reduce costs of commercial cultures. Key words: Oreochromis niloticus, tilapia, probiotics, lactic acid bacteria, yeast.