We present evidence for the overlap of two species of clingfishes, mountain clingfish (Gobiesox fluviatilis) and Mexican clingfish (Gobiesox mexicanus), in the Cuitzmala River, state of Jalisco, western Mexico. In addition to documenting novel sites where these species can be found, we present a new maximum standard length for G. fluviatilis, 137.8 mm. Morphometric and meristic variation in diagnostic characters for these species is higher than previously reported. We recommend a revision of diagnostic characters for Mexican freshwater clingfishes to better understand the systematics and distribution of species in the group.