This paper reports the results of a comparative study of the mandibular, hyoid, and pectoral musculature of South American Doradidae. Sixty-one species of Doradidae were examined including representatives of all the genera. Twenty muscles are described including their ontogenetic origin, function, area of origin and insertion, and parts. Seven muscles from the cranial region: adductor mandibulae, extensor tentaculi, levator arcus palatini, dilatator operculi, levator operculi, adductor operculi, and adductor arcus palatini; six muscles from the ventral region: intermandibularis, protractor hyoidei, hyohyoides inferioris, hyohyoidei abductores, hyohyoidei adductores, and sternohyoideus; and seven muscles from the pectoral fin: adductor superficialis, adductor profundus, abductor superficialis, abductor profundus, arrector ventralis, arrector dorsalis, and abductor rotator. Comparisons between Doradidae and other catfish families (e.g. Auchenipteridae, Aspredinidae) were made in order to understand and establish variations in position and shape of different muscles. A muscle not previously described for the pectoral fin of catfishes is described and named here as abductor rotator.