This species is distinguished from its congeners except G. hypostomus in having 5-16 (usually 9-13) large dark saddle-shaped pigment bars over the dorsal midline, extending between the nape and a vertical with the end of the anal fin, and sometimes reaching to or slightly below the lateral line; differs from G. hypostomus in having 141-172 (vs. 178-211) anal-fin rays; a shorter snout, preorbital distance 48.1-60.3% of head length (mean 54.6%) (vs. 58.3-68.6%, mean 63.9%); a larger eye, with diameter 5.7-9.0% of head length (mean 7.0%) (vs. 3.3-5.9%, mean 4.3%); a longer distance from tip of snout to posterior nares, 17.1-22.0% of head length (mean19.2%) (vs. 11.2-17.1%, mean 13.8%); 7 (vs. 9-13) displaced hemal spines; and 64-69 (vs. 71-75) vertebrae to end of anal fin (Ref. 87956).