Taxonomy & naming
Tetragonopterus anostomus was described in 2011 by Gabriel S. C. Silva and Ricardo C. Benine of IBB-UNESP, São Paulo, Brazil, in a paper published in Zootaxa (Vol. 2911, No. 1, pp. 50–56). The type material was collected from the rio Preto, a tributary of the upper rio Araguaia in the State of Goiás near Nova Crixás, and from a marginal lagoon near Cocalinho in Mato Grosso — both localities within the rio Araguaia drainage of central Brazil.
The genus Tetragonopterus belongs to the family Characidae, the largest family of characiforms. It has historically been taxonomically complicated, serving as a wastebasket group for many small South American tetras, but has been progressively revised and now encompasses a more restricted set of species with shared morphological characters. T. anostomus is distinguished from its four recognized congeners (T. argenteus, T. carvalhoi, T. chalceus, and T. rarus) by a combination of characters: its superior mouth position, number of premaxillary teeth, number of predorsal scales, overall colour pattern, and gill raker count. The Catalog of Fishes (Eschmeyer, CAS) records the valid name as Tetragonopterus anostomus Silva & Benine, 2011.
Morphology
Tetragonopterus anostomus reaches a maximum recorded total length of 5 in, making it a mid-sized species within the genus. Like other members of Tetragonopterus, it has a compressed, relatively deep characid body plan.
The species' most diagnostic morphological feature is its superior mouth — positioned at the top of the snout and directed upward — which is unusual among its congeners and the source of its species name. The original description also notes a comparatively enlarged maxilla and relatively small, numerous premaxillary teeth. Detailed meristic and morphometric data, as well as any distinctive colouration beyond general characid patterning, were published in the original Zootaxa description; the limited subsequent literature does not add substantially to what Silva and Benine recorded.
Habitat
Tetragonopterus anostomus occurs in freshwater pelagic environments within the upper rio Araguaia basin, one of the major river systems draining the Brazilian Cerrado (tropical savanna) of central Brazil. Confirmed collection localities include the rio Preto near Nova Crixás in Goiás and a marginal lagoon near Cocalinho in Mato Grosso.
The rio Araguaia is a large blackwater-to-clearwater river system with seasonal flooding. Marginal lagoons in the region are formed by the river's pronounced flood pulse, expanding during the wet season and contracting in the dry season. The species' occurrence in both the main tributary channel and associated marginal lagoons suggests some tolerance for varying hydrological conditions, though its ecological preferences across this range are not documented in detail beyond its characterisation as a pelagic freshwater species.
Feeding
No specific feeding data for Tetragonopterus anostomus has been published beyond its membership in Characidae. Members of Tetragonopterus are generally regarded as opportunistic omnivores or carnivores, taking small invertebrates, insects, and other food items available in the water column of their pelagic habitat.
The superior mouth position of T. anostomus is notable: in characids, an upward-angled mouth often indicates surface or near-surface feeding, potentially targeting insects and other items from the water surface or from the upper water column. This morphological inference, grounded in the functional anatomy of the jaw apparatus, is consistent with pelagic open-water habits, but direct dietary studies have not been conducted on this species.
Mating
No published observations of courtship or mating behaviour exist for Tetragonopterus anostomus. As a member of Characidae, it is expected to be an egg-scattering species with no parental care — the standard reproductive mode of the family — in which males pursue females and fertilise eggs as they are scattered among vegetation or over substrate.
Whether T. anostomus spawns seasonally in relation to the Araguaia's pronounced wet-dry flood pulse, as many Cerrado stream fishes do, has not been documented. The flood pulse typically triggers spawning migrations and reproductive activity in regional species, and T. anostomus, if seasonally tied to marginal lagoons, may follow a similar pattern. This remains inference from the regional ecological literature rather than species-specific data.
Breeding
No captive-breeding records for Tetragonopterus anostomus appear in the hobby or scientific literature. Based on the typical Characidae reproductive pattern, the species would be expected to deposit small, non-adhesive to slightly adhesive eggs scattered among fine-leaved plants or over the substrate, with no parental investment after fertilisation.
T. anostomus is not established in the ornamental fish trade and is effectively unknown to hobbyists. Any captive husbandry or breeding would be pioneering work. Inferences from related congeners suggest moderately warm, soft-to-neutral water conditions consistent with the Araguaia drainage, but no validated captive-breeding parameters have been published.
In the aquarium
Tetragonopterus anostomus is not known to be established in the aquarium hobby. It is a scientifically described species from the rio Araguaia basin of central Brazil, but has not entered the ornamental trade and there are no published hobbyist accounts of its care.
Based on its size — up to 5 in TL — and its classification as a pelagic open-water characid, a suitable aquarium would be spacious, with a long swimming lane and relatively open water column. The superior mouth suggests the fish may feed at or near the surface. Water parameters consistent with the Cerrado drainage of central Brazil — warm, soft-to-neutral — would be a reasonable starting point for any keeper who obtained specimens, but this is extrapolation rather than documented care data.
Conservation
Tetragonopterus anostomus has not been formally assessed by the IUCN Red List and carries a status of Not Evaluated (NE). The species is known from a restricted set of collection localities in the upper rio Araguaia drainage of Goiás and Mato Grosso, Brazil.
The rio Araguaia basin and the surrounding Cerrado biome face significant pressure from agricultural expansion, deforestation, and hydrological alteration driven by soybean and cattle farming across Goiás and Mato Grosso. The Cerrado is one of the world's biodiversity hotspots and one of the most threatened, having lost a substantial proportion of its original cover. Small, localised characids described from limited material in this region may be more range-restricted than current collection records indicate. A formal IUCN assessment would be valuable for determining whether T. anostomus warrants conservation concern.