Ichthyologists Carl H. Eigenmann and James Erwin Böhlke likened all members of Iguanodectinae, including Piabucus, to smelt.

[1][2] 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.

[3] 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.

[2] For instance, Piabucus dentatus has lateral line scales that reflect green in some lights, similar to Iguanodectes spilurus (the "green line lizard tetra");[8][9] P. dentatus' deeper pectoral keel and fin shape make the two relatively easy to differentiate.

[10] The dentition of Piabucus is relatively complete amongst characiform fishes, as is the case with the entire family Iguanodectidae (hence the name; "Iguanodectes" means "lizard bite").

[2] In 2011, research by Oliviera et al. showed that Bryconops was closely related to Iguanodectinae, and posited that the two clades be moved to the new family Iguanodectidae.

[22] However, "trutta dentata" is simply Latin for "toothed trout", which is one of the most general labels that researchers give to fish.

[23] Furthermore, the genus Trutta (now obsolete, synonymized with Salmo) was not available as a classification until 1764, upon proposition by French zoologist François Alexandre Pierre de Garsault.

[32] P. melanostoma lives in an area subject to regular flooding and takes advantage of bodies of still water left behind, feeding on plants, algae, and small invertebrates that are swept in.

[31][32] Piabucus, while taken from the wild for the ornamental fish trade, is not being collected at a high enough rate to warrant concern for the genus.

[33] P. melanostoma, while not assessed, is assumed to have a stable population due to its wide range, despite dispersion abilities limited by a flood-cycle wetland habitat.