Knodus is a genus of small characin fishes — true tetras — in the family Characidae, distributed widely across northern and central South America, with the atlas recording species from Brazil, Colombia, Venezuela, Peru, Ecuador, Bolivia, and Guyana. Members are typically slender, laterally compressed, silvery fish that school in the shallow margins and tributary creeks of Amazon and Orinoco basin drainages, feeding opportunistically on small invertebrates and organic matter drifting in the current. The atlas covers 32 species with a broad size range, from roughly 1 in up to species reaching about 5 in, wider than in most tetra genera, and outward appearance varies from plain silver to species with a dark humeral spot or fine dusky striping.
Data on Knodus as a whole are sparse, and that sparsity is itself telling: the atlas's IUCN tally shows the great majority of its species as Not Evaluated, reflecting a genus that has historically been difficult to separate on external characters alone and includes many recently described or still-debated species. Very few Knodus are marketed individually in the aquarium trade; where they do appear, it is typically as unlabeled bycatch mixed into general South American tetra shipments rather than as a targeted import. Knodus moenkhausii is one of the more frequently cited names in the ichthyological literature, but detailed captive-care information for the genus at large remains thin, and prospective keepers should expect to treat any Knodus largely as an unspecialized, community-friendly tetra pending better species-level data.