Evolution through adaptation may be determined by multiple and potentially interacting features of the environment and the phenotype of organisms. We are interested in the combined effects of two different ecological factors, water velocity and predation, on the evolution of morphology and life history of the species belonging to the genus Gambusia (Teleostei, Poeciliidae). Specimens from one or more populations from more than ten species were obtained from museum and personal collections. We chose only collections that counted with data on the predation and water velocity regimes in their locality of capture. All fishes were photographed to gather morphometric data, which was analyzed using geometric morphometrics. Females were dissected and measured to observe life history traits (size, weight, fecundity, mean embryo weight, and reproductive allocation). Morphometric results and life history data were analyzed using a comparative approach and univariate statistics. We concluded that morphometry and life history traits of the species of Gambusia studied were little affected by water velocity, but strongly affected by predation. In other words, morphology and life history were more affected by the biotic factor rather than by the abiotic factor. We will continue pursuing our main objective, to make an assessment of the effect of predation and current, on morphology, life history and locomotor performance for all the species of the genus Gambusia.