Parodon alfonsoi differs from its congeners in having a silvery blotch beneath the eye (vs. silvery suborbital blotch absent); a lateral stripe with conspicuous, dark, vertical projections along almost its entire length (from the opercle to the area above the anal-fin base origin) (vs. lateral stripe with inconspicuous vertical projections along its entire length or without projections). From P. suborbitalis it can be distinguished by the greater number of preanal scales (27-30 vs. 24-27); by the lower number of cusps on premaxillary teeth (11-14 vs. 15-17); and by the lower number of branched pectoral-fin rays (11-14 vs. 14-17). It differs from P. moreirai, P. pongoensis, P. caliensis, and P. apolinari by the presence of a lateral stripe with zigzag projections (vs. absence of lateral stripe with zigzag projections). From P. hilarii it is differentiated by the straight edge of the premaxillary teeth (vs. slightly rounded) and length of projections of lateral stripe (three scales vs. two scales). From P. nasus it is distinguished by elongated projections (vs. rounded projections) and in having the lateral stripe extending to the distal tip of the medial caudal rays (vs. absence of medial caudal rays with dark projection). It also differs in the number of preanal scales (27-30 vs. fewer than 27, except in P. hilarii which has up to 28); greater caudal peduncle depth (13.3-16.3% SL vs. 12.9-14% in P. atratoensis, 10.7-13.9% in P. buckleyi and 10.4-12.7% in P. pongoensis); in having no dark spots above the lateral stripe (vs. spots present above lateral stripe except in P. bifasciatus); and by the number of cusps in premaxillary teeth (12-14 vs. 15-19 in P. carrikeri; 7-12 in P. bifasciatus). It can be differentiated from P. guyanensis by the number of teeth in the premaxilla (four vs. five) (Ref. 88955).