Taxonomy & naming
Hoplias lacerdae was described by the Brazilian ichthyologist Alípio de Miranda-Ribeiro in 1908, with its type locality at Iporanga on the Rio Ribeira de Iguape in São Paulo State, Brazil; the holotype (MNRJ 211) measures 29.5 in standard length, essentially matching the largest sizes recorded for the species today. It belongs to the family Erythrinidae — the trahiras and wolf fishes — within the order Characiformes, a small Neotropical family of elongate, predatory characins that also includes the genera Erythrinus and Hoplerythrinus.
The genus Hoplias has undergone substantial taxonomic revision, with what was once treated as a single wide-ranging "Hoplias malabaricus" species complex split into numerous distinct species based on morphology and genetics; H. lacerdae is one of the larger-bodied, geographically restricted species recognised within that revision, confined to the Ribeira de Iguape drainage rather than ranging across the Amazon or Paraná like some of its relatives. The common name "trahira" (also spelled traíra) comes from Tupi and refers to the wolf-fish group generally; "lacerdae" honours a personal name, following the convention of many early twentieth-century Brazilian species descriptions.
Morphology
The giant trahira has the unmistakable Hoplias body plan: a long, thick, cylindrical trunk, a broad and somewhat flattened head, and a large mouth armed with heavy, conical, interlocking teeth designed for gripping and crushing prey rather than slicing it. FishBase records a maximum size of 29.5 in standard length and up to 4.3 kg, making it one of the larger species in its genus, and its build is powerful rather than streamlined — a fish adapted to explosive, short-range ambush strikes rather than sustained pursuit.
Colouration is typically a mottled olive-brown to greenish-grey over the flanks, camouflaging the fish against submerged wood and leaf litter in its home rivers, with a robust, rounded caudal fin. As an obligate air-breather, H. lacerdae must periodically surface to gulp atmospheric air, an adaptation shared across the genus that lets it tolerate oxygen-poor water that would be unlivable for most other fish.
Habitat
Hoplias lacerdae is restricted to the Ribeira de Iguape River basin spanning São Paulo and Paraná states in southern Brazil, a river system distinct from — and considerably smaller than — the Amazon or Paraná basins that host other, more wide-ranging Hoplias species. Within that drainage it occupies a benthopelagic niche in river channels and associated habitats, typically holding near cover such as submerged wood, roots and dense vegetation where it can ambush passing prey.
As an air-breathing species it tolerates a wide range of dissolved-oxygen conditions, including sluggish, vegetated backwaters that would be marginal for many fish. Its restricted single-basin distribution, combined with FishBase's note of high vulnerability to fishing pressure, makes habitat condition within the Ribeira de Iguape more consequential for this species than for the more widely distributed trahiras.
Feeding
Hoplias lacerdae is an obligate piscivore and one of the top predators in its native river system — FishBase assigns it a high trophic level (4.3) consistent with a specialist fish-eater rather than a generalist omnivore. It hunts by ambush, lying in wait near cover and striking explosively at fish that stray too close, then gripping and swallowing prey whole with its heavy dentition rather than tearing it apart.
In the aquarium it should be fed whole dead fish, smelt, sprats, mussels and worms — meaty, appropriately sized whole foods rather than fillets or flakes. It will attempt to eat any tankmate it can physically engulf, so feeding decisions and tankmate choices both have to be made around that single fact: nothing goes in the tank that isn't either far too large to swallow or intended as food.
Mating
Detailed courtship behaviour for Hoplias lacerdae specifically is not well documented, but the pattern reported for the genus and reflected in hobby breeding accounts involves an evening spawning event preceded by a period of pairing, during which a male selects and prepares a nest site. Spawning is associated with warm water in the mid-20s °C and a moderate, near-neutral pH, conditions consistent with the species' native subtropical Brazilian range.
No reliable external sexual dimorphism is documented for this species — data is sparse on this point, and hobbyist accounts do not describe a consistent colour or morphological difference between males and females outside of spawning condition.
Breeding
Hoplias lacerdae is a substrate nest-spawner: the male digs a hollow or nest in the substrate, and in an evening spawning event the female deposits several thousand eggs into it, which the male then guards. Parental care is male-only and reportedly attentive, with the guarding male driving off intruders from the nest site until the brood disperses — a pattern shared with other nest-building Hoplias and Erythrinus species rather than the open-water egg-scattering seen in many other characins.
Practical Fishkeeping reports breeding water conditions of roughly 79 °F and pH 6.0–7.5 for successful spawns. That said, the species is described as very rare in the aquarium hobby and hard to obtain, and captive breeding accounts are correspondingly scarce; most home aquarists will never encounter a breeding pair, and this is not a species to plan around producing in a typical home fishroom.
In the aquarium
This is an extreme-specialist fish, not a community or even a typical species-tank inhabitant. Practical Fishkeeping recommends a tank over 2 metres (roughly 6'5") in length with massive filtration to handle both the bioload of a fish that can reach 29.5 in and 4.3 kg and its whole-prey feeding habits. It should be kept alone — a single adult Hoplias lacerdae is powerful, predatory and will treat any fish it can swallow as food, and conspecifics or similarly sized tankmates are at serious risk of injury or death from an animal this size and temperament.
Provide dim lighting, sand or fine gravel, and secure driftwood or root hides, since trahiras in general are ambush predators that favour cover; as an air-breather it needs unobstructed access to the surface. Handling must be done with extreme caution and by container rather than net — the jaws and teeth of a fish this size can inflict a serious bite, and this is not folklore but a stated risk with any large Hoplias. Given its rarity in the trade and the scale of housing it demands, this species is appropriate only for experienced keepers with a genuinely oversized, dedicated setup.
Conservation
The IUCN Red List assesses Hoplias lacerdae as Least Concern, in an assessment dated 7 August 2020. However, FishBase separately flags the species as having high vulnerability to fishing pressure, and its distribution is restricted to a single river basin — the Ribeira de Iguape — rather than the broad multi-basin ranges enjoyed by many of its relatives, so its LC status should be read alongside that narrower range and fishing-pressure sensitivity rather than assumed to mean abundant and secure everywhere.
The species is very rarely seen in the aquarium trade, which limits any conservation impact from hobbyist collection; its main pressures, where documented, are more likely tied to fishing and habitat condition within its native Brazilian drainage than to the aquarium hobby.