Piabucus is a genus of freshwater tetras in the family Iguanodectidae. All three species are found in South America, largely the Amazon and its major tributaries. None of them are longer than half a foot long, with the largest reaching a maximum size of 12.9 cm (5.0 in), and they are slender, with relatively deep chests and long pectoral fins. Their scales are pale or silvery, with lateral lines that stand out. At least one species, Piabucus dentatus, is known to be collected for the aquarium industry. All three species are sometimes given the collective name "chin tetras" by sellers, in reference to markings on the lower jaw. However, none of the species are considered endangered, so capture of wild specimens is not an immediate threat to population numbers. As well as this, collection is not happening at a high enough rate to be of any concern. Piabucus has a close relative in the genus Iguanodectes. The two are paired in the subfamily Iguanodectinae, forming a clade. The genus Bryconops makes up a monogeneric sister clade, and the three genera together make up the family Iguanodectidae. There is minor, but ongoing, debate regarding Iguanodectinae and Iguanodectidae, as some authorities still list Piabucus in the family Characidae. Description As a genus, Piabucus are somewhat slender, rather minnow-shaped. Ichthyologists Carl H. Eigenmann and James Erwin Böhlke likened all members of Iguanodectinae, including Piabucus, to smelt. Though generally similar in appearance to the sister genus Iguanodectes, Piabucus can be told apart because it has a deeper chest and longer pectoral fins. The name "Piabucus" comes from the genus' general appearance; the word "piabucu" was used in 17th century Brazil to refer to various small characiform fishes. It has also been posited that "Piabucus" comes from "Piaba", a region of Barcelos, Brazil, and "bucca", meaning "mouth". All members of Piabucus are under half-a-foot long. The shortest (in standard length) is P. caudomaculatus at 9.6 cm (3.8 in), followed by P. melanostoma at 11.5 cm (4.1 in), and P. dentatus is the longest at 12.9 cm (5.0 in). This makes them slightly longer on average than Iguanodectes, whose size ranges from 4.6 cm (1.6 in) to 10.3 cm (4.1 in) SL. In all species, the lateral line is complete, and the scales therein often stand out from the rest of the body, which is covered in pale or silvery scales. For instance, Piabucus dentatus has