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Iguanodectidae is a family of freshwater fish in the order Characiformes that lives in South America. It contains three genera: Iguanodectes, Piabucus, and Bryconops. Several species in the family, such as the green line lizard tetra ( Iguanodectes spilurus), the tailspot tetra ( Bryconops caudomaculatus), and the orangefin tetra ( Bryconops affinis), are sometimes taken as aquarium fish.
Members of Piabucus are slightly larger than members of Iguanodectes, reaching a maximum of 12.9 cm (5.1 in), while members of Iguanodectes only reach 10.3 cm (4.1 in). They are slender and rather elongate in body shape, comparable to Minnow; ichthyologist Carl H. Eigenmann, who named the subfamily, likened them to smelt. Their scales are often brightly colored or reflective, and this, combined with their small size, makes them a potential target for the aquarium industry.
The dorsal fin is located behind the middle of the body and usually behind the start of the pelvic fin, though sometimes the dorsal and pelvic fins are on the same line of origin. All members of the subfamily have a small dorsal adipose fin. Piabucus typically have longer pectoral fins and a deeper chest than Iguanodectes (sometimes described as a more pronounced "pectoral keel"). (2025). 9788574303611, EDIPUCRS. ISBN 9788574303611 The lateral line is complete in all species. The species Iguanodectes geisleri has some morphological differences when compared to its congeners; its dorsal fin originates in the middle of the body, as opposed to behind the middle, and its anal fin is shorter in length.
The mouth is small, terminal, and does not extend past or under the eye. The maxilla is equipped with multicuspid incisor teeth, contracted at the base and flaring outwards. The premaxilla has one or two teeth on each side in all species, except for Piabucus melanostomus, which lacks this "outer set". This dentition is primarily used for an herbivorous diet, at least in Iguanodectes, but little is known of the subfamily's ecology outside of this.
They can be found in the Amazon River, Orinoco, Tocantins River, and Paraguay River rivers, as well as all major tributaries of the Amazon. (2025). 9788574303611, EDIPUCRS. ISBN 9788574303611 Of these, the Paraguay is the least-populated; Iguanodectinae is only represented therein by a few species in the genus Piabucus. When in captivity, species from both genera have been observed to be intolerant of poor water conditions, demonstrating a preference for a well-oxygenated environment. They seem to prefer swimming near the surface of the water.
Iguanodectidae contains the following genera: Iguanodectes is next-largest with 8, and Piabucus has the fewest at 3.
Iguanodectes and Piabucus are largely considered to make up the subfamily Iguanodectinae, with Bryconops becoming its own separate clade, but this is a matter of debate. Several sources accept the subfamily Iguanodectinae as its own entity, but others consider it synonymous with Iguanodectidae or simply don't acknowledge it, uniting the genera therein. ITIS considers it synonymous with Characidae, which is a reflection of its older classification.
Iguanodectinae, when first officially classified by Carl H. Eigenmann in 1909, was placed in the family Characidae, and only contained the genus Iguanodectes; by 1929, it had grown to include the genus Piabucus. Through the year 1977, this remained the case. In 2011, Iguanodectinae was found to be closely related to Bryconops, and the two clades were combined in Iguanodectidae.Oliveira, C., Avelino, G.S., Abe, K.T., Mariguela, T.C., Benine, R.C., Orti, G., Vari, R.P., & Correa e Castro, R.M. (2011): Phylogenetic relationships within the speciose family Characidae (Teleostei: Ostariophysi: Characiformes) based on multilocus analysis and extensive ingroup sampling. BMC Evolutionary Biology, 11: 275. doi: 10.1186/1471-2148-11-275
Accessed on 03 February 2022. Bryconops colaroja
Accessed on 03 February 2022. and Piabucus dentatus
Accessed on 03 February 2022. are seen in the ornamental fish trade. Iguanodectes geisleri is rare, but is sold under the name "red line lizard tetra". One of its congeners, Iguanodectes spilurus, is called the "green line lizard tetra", and is sensitive to poor water conditions.
Though not as popular as many other species of tetra, several members of Iguanodectinae are seen in the aquarium trade. Piabucus dentatus, sometimes called the Piabuco tetra, is taken from the wild for such purposes, but is not at risk of going extinct from it.Taphorn, D.C., DoNascimiento, C., Herrera-Collazos, E.E., RodrÃguez-Olarte, D., Usma, S. & Villa-Navarro, F. 2021. Piabucus dentatus. The IUCN Red List of Threatened Species
Accessed on 08 February 2022. Reports from hobbyists as recently as "the summer of 2018" show that such collection is still ongoing. It tends to form groups, so aquarists are recommended to house as many as at least 6 at a time. This goes for the other species of Piabucus as well; all three are sometimes grouped as Piabucus sp. and called "chin tetras". This is likely due to distinct markings on the lower jaw.
Fish from Iguanodectes are slightly more common than from Piabucus, but are still infrequent in the trade. I. geisleri is sold under the name "red line lizard tetra", and I. spilurus has the name "green line lizard tetra". I. adujai looks quite similar to I. geisleri, so is sometimes part of the same stock.
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