Brachyrhaphis is a genus of small livebearing fish in the family Poeciliidae, native to Central American streams from Panama and Costa Rica north through Nicaragua, Guatemala, and Mexico. Like their poeciliid relatives, Brachyrhaphis bear live young rather than laying eggs, with males distinguished by a smaller size, brighter coloration, and a modified anal fin — the gonopodium — used in mating. Most species stay under 2.5 in and inhabit clear, fast-flowing streams and headwaters rather than the sluggish ponds favored by many other livebearers.
Brachyrhaphis is better known in evolutionary biology than in the aquarium trade: several species, especially the bishop toothcarp (B. episcopi), have been central to decades of field research on how predation pressure shapes body size, coloration, and life-history traits in stream fish, comparing populations that share a river with predatory species against those that don't. In the hobby, they appeal mainly to livebearer and native-fish specialists rather than general keepers. Many Brachyrhaphis populations are narrowly distributed to a single river system, and the atlas's conservation tally shows real cause for concern — Data Deficient, Near Threatened, and Vulnerable ratings dominate, with only two species reaching a clean Least Concern.