Piabucus dentatus

Piabucus dentatus reaches a maximum length of 12.9 cm (5.1 in) SL (standard length), which makes it the largest of its genus. It has a generally slender body with a deep chest and long pectoral fins, which are characteristics that differentiate Piabucus from sister genus Iguanodectes. It is elongated and slight, with a compressed "torpedo" shape. It has a generally silvery color with a dark lateral stripe; its scales may reflect blue light ventrally, and its lateral line may contain yellow-gold and green. Congener Piabucus melanostoma has a distinctive patch of dark coloration on the lower jaw often absent in related species, but similar markings can be found on some specimens of P. dentatus. The presence of an adipose fin can be used to differentiate P. dentatus from its similar congeners. Notable morphometric characteristics include 80-84 perforated scales in the lateral line, 11 dorsal-fin rays, and 45-46 anal-fin rays. The dorsal and ventral fins are short, and the middle rays of the caudal fin are often pigmented, but the fins otherwise lack markings. Juvenile P. dentatus have rounder heads, smaller mouths, and a body that is proportionally elongate. Starting at a length of roughly 2 cm, juveniles start to resemble small adults.

Sexual dimorphism. Sexual dimorphism is minor in P. dentatus, but present. …

Piabucus dentatus is a coastal dweller, found in river drainages from Venezuela's Paria Gulf to the mouth of the Amazon river. It demonstrates a preference for silty, turbid waters, including estuaries, floodplain streams, and various river tributaries, which places it in some brackish environments. Ichthyologist Carl H. Eigenmann once mistakenly cited it from Peru, and further instances from Bolivia are misidentifications. Though infrequent, it is found in Suriname.

Examination of stomach contents has shown that P. dentatus is a generalist feeder with a preference for algae and decaying plant matter, though it also targets microscopic invertebrates. Its varied diet earns it different classifications across various studies; it is classified as a detritivore based on its consumption of leaf litter, a micropredator based on its consumption of micro-invertebrates, or an algivore based on its consumption of various types of algae. Piabucus dentatus is known to be a schooling fish with a non-confrontational temperament. It tends to dwell near the surface of the water, and is often an active swimmer. Little is known of specific reproductive habits, but aspects of its biology indicate that it is likely an egg-scattering species that does not guard its young.

Presence and behavior in aquaria. While P. dentatus is known from the aquarium trade, and congeners are also seen in the industry, information on species-specific behavior and care is somewhat limited. Hobbyists report a generally pleasant disposition, but its large size in comparison to other aquarium tetras results in an intimidating presence for smaller fishes; still, it is often an appropriate addition to a community tank. It is known to be a generalist feeder that will accept most flake and pellet food, as well as biting at soft-leaved aquarium plants and hair algae.

The specific epithet "dentatus" refers to the dense set of 16 teeth present at the end of each mandible, as "dentatus" means "teeth". "Piabucus" is a Latinization of the Brazilian word "piabucu", which was and is used to refer to various small fishes of similar appearance. The common name "chin tetra" actually originates from markings seen on Piabucus melanostoma. P. melanostoma has a dark patch on the lower jaw, but is otherwise similar to its congeners, which means that all three are sometimes referred to by the same common name. The common name "coastal piabucus" comes from the fact that P. dentatus is common in estuaries and brackish waters along the northeastern coast of South America.