Among the wide variety of tilapias, Nile tilapia (Oreochromis niloticus) is the most common in aquaculture and the need for a systematic effort to secure and to further improve the genetic quality of farmed stocks is widely recognized (BENTSEN et al., 1998). The growth of some species of fish has been improved by selection programs and many farmers consider it the main characteristic of performance. Thus, the search for tilapia strains of superior performance is becoming more and more frequent by producers, because of the increasing demands for healthy food, among the world population (SANTOS et al., 2008). This demand has required assessments of these fish cultured in different environments.