Distinguished from all 32 congeners except for some specimens (over 30.0 cm) of Gymnotus ardilai from the Río Magdalena drainage in northwest South America in having a pigmentation pattern in which the oblique dark-pigmented bands are faint, and difficult to distinguish from the ground color. Diagnosed from Gymnotus ardilai in having a shallower body depth (7.4-9.1 % TL [mean 8.2] vs. 11.4-13.2 [12.3]). Differs also from all species in the Gymnotus pantherinus species-group (and is placed in the Gymnotus carapo species-group) by the presence of two (vs. one) laterosensory canal pores in the preopercular-mandibular series of the dorsoposterior portion of the preopercle. Can be differentiated from all species in the Gymnotus carapo species-group that occur south of the Amazon basin except Gymnotus inaequilabiatus in having a much shallower body depth (7.4-9.1 % TL [mean 8.2] vs. 8.9-11.6 [mean 11.1] in Gymnotus bahianus, 9.8-10.3 [mean 10.1] in Gymnotus paraguensis, and 10.3-13.1 [mean 11.7] in Gymnotus sylvius). Differs further from Gymnotus inaequilabiatus in possessing a substantially narrower head (53.1-59.3 % HL [mean 57.5] vs. 65.3- 72.0 [mean 67.8]) (Ref. 75065).

Description: Pectoral fin with single large anterior unbranched rays and 13-15 branched rays (Ref. 75065).