Taxonomy & naming
Hoplias curupira was described in 2009 by Osvaldo Oyakawa and William Mattox as part of a broader revision that split the once-catch-all "Hoplias malabaricus" species complex into multiple distinct species across the Amazon and Orinoco basins. It belongs to the family Erythrinidae — the trahiras and wolf fishes — within the order Characiformes, a family of just a handful of genera (Hoplias, Erythrinus, Hoplerythrinus) of predatory, air-breathing Neotropical characins that are only distantly related to the true piranhas of Serrasalmidae despite sharing a fearsome reputation.
The species epithet honours Curupira, a red-haired, backward-footed trickster spirit who protects the forest and its animals in Tupi-Guaraní mythology — a fitting namesake for a reclusive ambush predator that spends most of its life motionless and hidden among cover. In the trade Hoplias curupira is generally sold as the "black wolf fish," a name it shares loosely with other dark-bodied Hoplias species, so buyers should confirm the scientific name rather than relying on the common name alone.
Morphology
Hoplias curupira has the classic trahira build: an elongated, cylindrical, faintly compressed body, a broad head with a large upward-angled mouth, and heavy, conical, dagger-like teeth set in strong jaws built for seizing and holding prey rather than slicing it. FishBase records a maximum of 12 in standard length for the species from sampled specimens, but aquarium and field sources describe wild individuals reaching approximately 29.5 in total length, with captive fish more commonly settling around 15.5 in — a substantial gap that likely reflects how few large wild specimens make it into formal length records.
Colouration is dark and mottled, typically blackish to dark brown over the body with irregular blotching, consistent with an ambush predator that relies on camouflage against submerged wood and leaf litter rather than open pursuit. Like other Erythrinidae, Hoplias curupira is a facultative air-breather, able to gulp atmospheric oxygen to survive in the poorly oxygenated, sluggish backwaters and flooded forest pools where it often hunts.
Habitat
Hoplias curupira is known from a broad stretch of the Amazon basin, including the rios Capim, Tocantins, Xingu, Tapajós, Trombetas and Negro, with records extending to the upper Orinoco near the Casiquiare and to coastal rivers of Guyana and Suriname. Within that range it occupies the sluggish, structurally complex margins of rivers and floodplain habitats — leaf litter banks, submerged wood and root tangles, and flooded-forest pools — where it lies in wait rather than roaming open water.
Water across its range is warm and mildly acidic to neutral; aquarium-trade sources give a working range of roughly 75–82 °F and pH 6.0–7.5. As with many Amazonian ambush predators, structure matters more than precise chemistry: cover to hide against is what lets the fish hunt the way it is built to hunt, and its air-breathing capacity gives it tolerance for the low-oxygen conditions typical of dense flooded-forest and backwater habitat.
Feeding
Hoplias curupira is an unambiguous ambush predator. FishBase and general-natural-history sources describe a diet of insects, insect larvae, small fishes, shrimps, worms and occasional fallen fruit, and stomach-content data from Orinoco specimens specifically record Macrobrachium shrimp, juvenile cichlids and Leporinus among prey items — evidence that this species readily takes other fish, including other predatory characins, whenever it can catch them. Sources also note it appears more diurnally active than some of its Hoplias relatives, hunting rather than lying dormant through daylight hours.
In the aquarium, Hoplias curupira is a committed fish-eater that will attempt to swallow prey up to close to its own size, and keepers should expect it to treat any tankmate small enough to fit in its mouth as a meal. It takes whole fish, prawn and other meaty foods readily; like many specialist piscivores it can be reluctant to accept dry or prepared foods, and tankmates must be chosen strictly on the basis of being too large to be swallowed, not merely "tough" or fast.
Mating
No species-specific courtship account for Hoplias curupira was found in the cited sources. What is documented is the pattern for the wider Hoplias genus: males excavate a shallow pit in the substrate as a nest site and spawning is reported to take place in the evening, with no unusual or extreme water-parameter demands beyond the fish's normal warm, mildly acidic-to-neutral range (around 79 °F, pH 6–7.5 in the sources describing genus behaviour). Nothing specific to sexual dimorphism or pair formation in Hoplias curupira is documented in the cited material, and this account does not extend that genus-level pattern to this species as confirmed fact.
Breeding
The genus Hoplias is described in aquarium and hobbyist literature as substrate nest-spawning: the male digs a shallow pit and a single spawning event can produce a cluster of 2,000 to 10,000 yellowish eggs, which the male then guards, along with the resulting larvae, until they disperse from the nest. This is a genuinely different reproductive strategy from the open-water egg-scattering typical of many characins, and it means paternal care — not maternal or biparental care — is the pattern reported for the genus.
Captive breeding of Hoplias curupira specifically is not documented in the sources reviewed for this article; the nest-spawning, male-guarding pattern above is known from congeners in the genus, not from this species directly, and this account should be read as "the genus pattern, not yet confirmed for H. curupira" rather than as an established aquarium breeding record. Prospective breeders should treat successful captive spawning of this species as effectively unreported.
In the aquarium
Hoplias curupira is not a community fish under any circumstances. It is a solitary predator that should be kept alone, in a large aquarium — a commonly cited minimum is around 120 US gallons (roughly 120 US gal) — with heavy cover from driftwood and robust decor that can withstand a large, powerful fish. Sources describing the species in the trade note it is aggressive not only toward conspecifics and tankmates but toward the keeper as well, gill-flaring and striking viciously at objects, hands or nets that intrude on its space; any tankmate must be robust and dramatically larger than the wolf fish to have any chance of being left alone, and most keepers simply do not attempt tankmates at all.
Water should be kept warm, roughly 75–82 °F, with a mildly acidic to neutral pH of about 6.0–7.5, and filtration strong enough to handle a large, messy piscivore's bioload. Because the species is a facultative air-breather, a secure, well-fitted lid is essential — Hoplias regularly surface to gulp air and are capable, powerful jumpers, and an uncovered tank is an easy way to lose one. Given its confirmed size potential in the wild (to roughly 29.5 in) and its documented aggression, this is a fish for an experienced keeper with the space and the caution to match, not a display centrepiece for a mixed tank.
Conservation
Hoplias curupira is assessed by the IUCN Red List as Least Concern, with the assessment dated 2020. This reflects its wide distribution across multiple major Amazon tributaries and into the upper Orinoco and Guiana coastal drainages, and the absence of evidence for significant population decline across that range.
As with many broadly distributed Amazonian fish, the species is not currently a conservation priority, but the general long-term pressures on the basin — damming, deforestation-linked habitat and water-quality change, and, for larger-bodied predatory fish, some level of collection for the aquarium and food-fish trade — remain relevant background context even though they are not flagged as an active threat to this species specifically in the cited assessment.