Genetic Variation is considered a support point to conserve and to manage the natural resources a world level. It determination is carried out by means of biochemical or molecular markers where the isozymes and alozymes have been the first and more used to evaluate the structure, abundance, and distribution of many ictic species based on estimation of genetic variation, characterizing for example, stocks or the potentiality of the species for cultivation. In the case of the lined catfish Pseudoplatystoma fasciatum (Linnaeus, 1766) distributed in the Magdalena’s basin and the Amazon, certain structural differences were observed starting from the electrophoretic pattern of 10 locus corresponding to: ME-1, mMDH-A, α-EST-1, α-EST-1, PGM, G6PDH, ADH-1, ODH, AO-1 and FUM. It were recognized in a preliminary way some exclusive alleles and/or others of low frequency for Leticia (Amazons) and La Dorada (Magdalena). Most of the analyzed systems were monomorphic in Magdalena, except for the α-EST-1 and in Amazon a similar proportion existed between monomorphic and polimorphic genotypes, with 5 monomorphic locus (ODH, AO-1, mMDH-A, ADH-1 and α-EST-1). However these differences didn’t correspond to a high variability, since many genotypes presented low frequencies. In such way the relative heterogeneity (Fst:0.2797) is based on the reproductive isolation by the geographical conditions of the basins, where the variability should be evaluated in a intrapopulations level in order to have a clearer idea of the current dynamics of each basin. The individuals possibly suffer dispersive or systematic processes that would explain the coexistence of deleterious genes. This study is expected to be the base for a global analysis of this endemic biological-fishing resource in Colombia to grand the relevance of updated projects that contribute the knowledge on the structure and genetic variation of different species that habit the native territory, without forgetting the fundamental role that plays the relationship between the conservation and the sustainable exploitation for the economy and biodiversity of the country.
