Taxonomy & naming
Hoplias auri was formally described in 2021 by Guimarães, Rosso, González-Castro, Souza, Díaz de Astarloa and Rodrigues, part of a wave of species-level splits carved out of the notoriously wide-ranging Hoplias malabaricus species complex using a combination of DNA barcoding and traditional morphology. It belongs to the family Erythrinidae — the trahiras and wolf fish — within the order Characiformes, and to the genus Hoplias, whose name derives from the Greek hoplon, "weapon," a direct reference to the powerful, heavily toothed jaws shared across the genus.
The species epithet auri comes from the Latin aurum, "gold," a reference to gold deposits mined in the Crepori River basin, the type locality and — as far as current records show — the only place the species is known to occur. Because H. auri was only recently split from the H. malabaricus complex, older literature, hobby records and trade listings referring to "Hoplias malabaricus" from the Tapajós drainage may in fact refer to this species or to other recently described segregates; this taxonomic churn means identification of trahiras in the trade should not be taken at face value.
Morphology
Hoplias auri has the classic trahira build: an elongate, cylindrical, heavily muscled body, a large depressed head, and a wide mouth armed with strong conical teeth suited to gripping prey rather than slicing it. The original description gives a maximum recorded size of roughly 12.5 in standard length, though as with other Hoplias, total length in life — including the caudal fin — runs somewhat longer, plausibly into the high 30s or low 40s of centimetres; no larger wild or aquarium specimens appear to be documented yet given how recently the species was described.
Colouration and fine-scale morphological detail distinguishing H. auri from its closest relatives in the H. malabaricus complex rest on the combination of meristic counts, morphometrics and DNA barcoding used in the original description rather than on a single obvious external field mark, which is typical of this species complex — many of its members look broadly similar to the naked eye and are difficult to tell apart without genetic or detailed morphological work.
Habitat
Hoplias auri is known from the Crepori River, a clearwater tributary of the Tapajós River in the Amazon basin, Pará State, Brazil — a Neotropical South American drainage, not African or Asian. As currently documented it appears to be endemic to this river system; no other populations have been reported in the available literature.
Like other Hoplias, it is presumed to favour the still or slow-moving margins of the river — backwaters, submerged wood and marginal vegetation — where an ambush predator can lie motionless and strike, though detailed habitat notes specific to H. auri are not available. General water chemistry for the wider genus in Amazonian tributaries runs warm and soft to moderately hard, roughly pH 6.0–8.0 and 68–79 °F, but river-specific data for the Crepori itself is not documented in the sources available here.
Feeding
Hoplias auri is a piscivore, and every member of this genus is built around the same strategy: rather than actively pursuing prey, a trahira spends most of the day motionless on the bottom or tucked into cover, using a powerful sense of smell and sensitivity to water movement to track passing fish before lunging forward in a single explosive burst to seize it. This ambush-and-engulf strategy, rather than sustained pursuit, is why the genus carries such heavy, weapon-like dentition rather than the slicing teeth of a piranha.
In the aquarium this translates directly: Hoplias take meaty foods — whole fish, prawn and similar — readily, and like other Hoplias, individual specimens can be reluctant to accept dry or prepared foods. Any tankmate must be too large to be swallowed whole, and in practice that describes almost nothing suitable, since a settled trahira will treat nearly any fish that fits in its mouth as a meal, not a neighbour.
Mating
No courtship or spawning behaviour specific to Hoplias auri has been documented; the species was described from preserved museum material and the original description does not report field observations of reproduction. Data is sparse for this species specifically, and nothing should be inferred beyond what is known for the genus as a whole.
Breeding
Breeding has not been documented for Hoplias auri, either in the wild or in captivity. Several other Hoplias and the related genus Erythrinus are known to be substrate nest-spawners, with a guarding male defending a pit or a nest among plants and tending the fry after hatching, but this mode has not been confirmed for H. auri specifically, and the species is not known to have been bred in aquaria. Given how recently it was described and its apparent restriction to a single river system, captive breeding records for this exact species should not be assumed to exist.
In the aquarium
Hoplias auri is not a community fish, and prospective keepers of any trahira should plan around a single, solitary predator rather than a display tank. Practical accounts of the genus recommend a species-only setup of 90 US gal or more, a tight-fitting, secured lid — Hoplias are strong enough to push through gaps and can strike hard at the surface — robust filtration such as a canister or sump to manage a heavy bioload and biweekly water changes to keep nitrate low, and cover in the form of rock or driftwood the fish can retreat behind before ambushing food.
Handling deserves particular caution: adult trahiras are powerful, genuinely aggressive fish with a serious bite, and this is a specialist's fish, not a beginner predator kept for shock value. Given that the species is only known from a single Brazilian river and was described in 2021, availability in the aquarium trade is likely to be limited or nonexistent, and any fish sold under this name should be treated with skepticism absent clear documentation, given how recently it was split from the wider H. malabaricus complex.
Conservation
Hoplias auri has not yet been assessed by the IUCN Red List and currently carries no formal conservation status (Not Evaluated). This is unsurprising for a species described only in 2021, but it also means there is no baseline population or threat data specific to this fish.
What is documented is that H. auri appears restricted to a single river system, the Crepori, a tributary of the Tapajós — and that basin is subject to gold mining pressure, a detail underscored by the species' own name, which references gold deposits in the Crepori basin. A geographically narrow range combined with mining activity in its only known habitat is worth flagging as a watch item even though no formal assessment yet exists; a proper conservation status will require a dedicated IUCN evaluation.