Serrapinnus zanatae is distinguished from its congeners by the following characters: premaxillary teeth with 7-9 cusps (vs. 10-12 cusps in S. gracilis and S. littoris, and 3-5 cusps in S. microdon and S. potiguar; spatulate and parallel ventral procurrent caudal-fin rays (vs. scimitar-shaped procurrent caudal-fin rays arranged in a semi-circle in S. aster and S. potiguar); incomplete lateral line (vs. complete lateral line in S. heterodon, sometimes also complete in S. sterbai and S. tocantinensis; dorsal fin without markings (vs. black pigmentation on the anterior and proximal border of the dorsal fin in S. notomelas and a faint black blotch on the distal half of the dorsal fin in S. microdon and S. heterodon); dark longitudinal stripe extending from the region below the dorsal fin to the caudal peduncle (vs. dark longitudinal stripe extending from the region anterior to the pseudotympanum to the caudal peduncle in S. sterbai); abdomen without distinctive marks ( vs. abdomen with a black spot on the posteroventral region in S. kriegi); absence of fins rays extended as filaments (vs. unbranched dorsal-, pelvic- and anal-fin rays extended as filaments in mature males in S. tocantinensis); 11-13 ventral procurrent caudal-fin rays (vs. 13-16 in S. calliurus, 14-16 in S. kriegi, 17-19 in S. lucindai, and 13-16 in S. micropterus); 16-19 branched anal-fin rays (vs. 19-22 in S. calliurus); 33-36 scales on longitudinal series (vs. 31-32 in S. micropterus); caudal-fin spot oval and horizontally elongated not extending to dorsal and ventral margins of the caudal peduncle (vs. caudal spot usually lozenge, vertically elongated, reaching the dorsal and ventral margins of the caudal peduncle in S. calliurus and S. piaba (Ref. 119705)).