Megadontognathus is a genus of weakly electric ghost knifefish in family Apteronotidae, the group within the South American order Gymnotiformes that generates a continuous weak electric field for navigation and communication rather than for defense. The genus is known from river systems in Venezuela and Brazil, and like other apteronotids it has the family's signature body plan: an elongate, laterally compressed trunk that tapers to a whip-like tail, no dorsal fin, and a long electric-organ-bearing fin running most of the length of the underside. The atlas covers 2 species, both around 10 in, a larger size than many of the genus's ghost-knife relatives.
Megadontognathus has essentially no presence in the aquarium trade. Ghost knifefish popularity in the hobby centers on a handful of easier, better-known apteronotids such as the black ghost knifefish, and species this poorly known stay in the domain of ichthyological collections rather than fish stores. The conservation picture drawn from the atlas is a concern for a genus this small: of the two species covered, one is assessed as Critically Endangered and the other as Vulnerable, pointing to real pressure on the rivers these fish depend on even though detailed threat data are sparse.