Otolith shape is widely used as a taxonomic feature in fish systematics. In Siluriformes, the lapillus otolith is the most relevant character for taxonomic purposes, although its discriminant potential has not been assessed quantitatively. Our study model were sea catfishes of the family Ariidae from the north-eastern Pacific as representatives of Siluriformes, a taxon with increased taxonomic complexity. The lapillus otolith shape obtained by geometric morphometrics showed high discrimination potential both at the genus and species levels with an overall classification accuracy of c. 93% (K = 0.92). Due to the strong species delimitation exhibited by lapillus otolith shape, the descriptions and identification keys provided here are the most useful materials to recognize the eight sea catfish species evaluated. The shared similarities in lapillus otolith shape among species seem to be more influenced by phylogenetic relationships than other factors such as habitat. The lapillus otolith shape is the most powerful taxonomic feature discovered so far for the identification of sea catfishes from the north-eastern Pacific.