Taxonomy & naming
Erythrinus guavina was described by the German naturalist and explorer Alexander von Humboldt in 1821, one of a handful of fish species he named from specimens collected during his South American expeditions. It belongs to the family Erythrinidae — the trahiras or wolf fishes — within the order Characiformes, a small family of just three genera (Erythrinus, Hoplias and Hoplerythrinus) united by an elongate, cylindrical body, a large predatory mouth and the ability to gulp atmospheric air.
The genus Erythrinus is distinguished from the more heavily built Hoplias by a more slender profile, and species-level identification within the genus is difficult; museum and field records for the genus are frequently reported only as Erythrinus sp. Data specifically attributed to E. guavina is limited in the available literature — GBIF confirms the name as a valid, recorded taxon, but detailed biological accounts most often describe the better-documented congener E. erythrinus (red wolf fish), and general Erythrinus/Erythrinidae biology is used here as a guide where the species itself has not been separately studied.
Morphology
Erythrinus guavina has the classic erythrinid build: an elongate, rounded, torpedo-like body, a broad flattened head and a large mouth armed with heavy, conical, well-spaced teeth built for gripping and puncturing rather than shearing. The dorsal fin sits well back on the body, the tail is rounded, and the overall silhouette is built for a slow stalk followed by a short, explosive strike rather than sustained pursuit.
Maximum size for E. guavina specifically is not documented in the sources available (data sparse). Within the genus, Erythrinus species are medium-sized trahiras — smaller than the largest Hoplias (H. aimara can exceed a metre) but still a substantial predatory fish as adults, and any aquarist should plan for a fish considerably larger than a typical community characin rather than assume a small, manageable size.
Habitat
Erythrinus guavina is native to South America, recorded from the Orinoco and Amazon basin drainages. Erythrinidae as a family are characteristic fish of Neotropical floodplains, favouring vegetated lakes, flooded forest and slow, often oxygen-poor backwaters and swamps where their accessory air-breathing organ — a modified, vascularized swim bladder — lets them survive conditions that would suffocate most fish. They are nocturnal ambush hunters that rely on dense cover (submerged wood, roots, aquatic vegetation) to lie in wait rather than actively roam open water.
Specific water chemistry data for E. guavina was not found in the available sources. Broadly, Erythrinidae inhabit warm, typically soft and slightly acidic South American lowland waters consistent with Amazon and Orinoco floodplain conditions, but precise temperature and pH figures for this species should be treated as unconfirmed rather than assumed.
Feeding
Erythrinus guavina is a piscivorous ambush predator. Erythrinidae as a family are documented nocturnal hunters that take fish as adults, with juveniles feeding more on crustaceans and insect larvae before graduating to a fish-based diet. It strikes from cover rather than chasing prey in open water, engulfing anything it can fit in its mouth.
In the aquarium, the closely related E. erythrinus refuses dried foods and is maintained on meaty foods — earthworms, prawns and whole or cut fish — and there is no reason to expect E. guavina to differ. Any tankmate must be too large to be swallowed whole; this is not a fish that can be trusted with smaller companions of any kind.
Mating
No specific courtship account for Erythrinus guavina was found in the available sources (data sparse). Within the wolf-fish family, several Hoplias and Erythrinus species are known to pair off and establish a nest site — typically a cleared pit in the substrate or a patch among plants or roots — ahead of spawning, with the male taking on a territorial, defensive role once a site is chosen. Whether this applies to E. guavina specifically has not been confirmed.
Breeding
Breeding biology for Erythrinus guavina is not established in the sources reviewed. Several trahiras (Hoplias and Erythrinus species) are documented as substrate nest-spawners, in which the male guards a pit or plant-associated nest and stands watch over the eggs and fry, but many species in the family are only rarely — if ever — bred in captivity, and no aquarium or commercial breeding reports for E. guavina specifically were found.
Given the sparse documentation, this species should be considered essentially unbred in the hobby. A prospective keeper interested in breeding trahiras is better served researching the handful of Hoplias/Erythrinus species with confirmed captive-breeding accounts than assuming E. guavina will follow the same pattern without direct evidence.
In the aquarium
Erythrinus guavina is a predatory specialist, not a general aquarium fish, and should be kept alone or with tankmates far too large to be viewed as prey. Provide a spacious tank with a tight-fitting lid — air-breathing fish of this kind regularly surface to gulp air and are capable jumpers — along with dense cover from driftwood, roots or robust plants where the fish can lie in ambush, since a bare, brightly lit tank is a poor match for a nocturnal, cover-dependent hunter. Filtration should be strong given the fish's size and largely meaty, high-protein diet.
Because maximum size and precise water parameters for this species are not well documented, keepers should err toward a generously sized setup and stable, moderate tropical conditions rather than assume the small end of the genus's range. As with any large, toothy predatory characin, handling should be done with a container rather than bare hands or a thin net.
Conservation
Erythrinus guavina has not been evaluated by the IUCN Red List; its status is Not Evaluated. This is common for many South American characins and erythrinids that are not targeted by major fisheries or the aquarium trade and therefore fall outside the scope of most conservation assessments to date.
No species-specific threats or population data were found in the available sources. Broadly, freshwater fish across the Amazon and Orinoco basins face long-term pressures from damming, deforestation-linked sedimentation and water-quality change, and these are relevant background considerations for the species even though no direct assessment exists.