Vital statistics of a population of a non native freshwater fish, the guppy Poecilia reticulata Peters, 1859 from a semi-abandoned pond nearby Santa Marta, Colombia, are reported. Estimates include growth, mortality, length-weight relationship, sex ratio and male versus female numbers and sizes. Von Bertalanffy growth parameters were found typical of the species, growth form was isometric for both sexes and under lab versus field conditions, and females were significantly more numerous and bigger than males. Results were compared to published data and the plasticity of this species is discussed.