Tembeassu is a genus of South American electric knifefish in the order Gymnotiformes, known from Brazil and comprising two described species, Tembeassu marauna and Tembeassu titanicus, both reaching a modest size around 7.5 in. Like other gymnotiforms, they are elongate, weakly electric fish that navigate and locate prey using a self-generated electric field sensed through an organ running the length of the body, and they are active mainly after dark rather than in open, sunlit water.
This is a genus of essentially scientific rather than hobby interest; it has no meaningful presence in the aquarium trade, and detailed field or husbandry data are sparse. Both atlas species currently carry a Critically Endangered IUCN assessment, which points to a genuinely narrow range and significant pressure on their habitat rather than simple undersampling. Freshwater fish restricted to specific Brazilian river reaches are especially vulnerable to damming, sedimentation, and other alterations of natural flow.