A preliminary morphometric study based on 17 landmarks was carried out, using 104 specimens of six species of sea catfishes from both South American coasts, the four accepted species of the genus Bagre and two reference species (Ariopsis seemanni and Arius platypogon). The landmarks were mainly located on the head and at the origin and end of fins. The partial warps weighted matrix was used to perform the discriminant analysis and the species pair-wise comparisons in order to establish if there were differences between the species. Thereafter, a partial-warps weighted matrix was generated with the average species consensus. Using PHYLIP maximum likelihood routine (CONTML), an additive tree was obtained. Shape changes were described over the tree using TPS tree (square change parsimony). Bagre marinus (western Atlantic) seems to be the most basal species of the genus. The species showing the larger shape changes are B. pinnimaculatus (eastern Pacific) and B. bagre (western Atlantic). Those two species are apparently more closely related to each other than to the other two species of Bagre.