A new species of Gymnotus Linnaeus is described from Riacho Cambiriba a clear water stream, tributary of the Rio de Contas basin, Bahia, northeastern Brazil. The new species is a member of the G. carapo species-group, which is characterized by the presence of a transparent patch near the posterior end of the anal fin and two (vs. one) laterosensory pores in the dorso-posterior region of the preopercle bone. Gymnotus interruptus may be diagnosed by a unique combination of morphometric and meristic characters: wider interorbital distance (44.6 – 45.9% of STO); 9 scales above lateral line at midbody; 23 – 28 ventrally oriented lateral line rami; 37 – 40 pored lateral line scales to first ventral ramus of lateral line; shorter snout (29.6 – 30.5% of STO). Gymnotus interruptus, the first record of a gymnotiform fish from the rio de Contas basin, may be easily distinguished from G. carapo or G. bahianus, two congeners also occurring in northeastern Brazil, by its colour pattern, in which the pale interbands, anterior to vertical through first ventral lateral line ramus, are ventrally and/or dorsally fragmented, allowing union of adjacent dark bands

Banded Knife-fish; Description; Biodiversity; Neotropical