Taxonomy & naming
Erythrinus kessleri was described by the Austrian ichthyologist Franz Steindachner in 1877, with a type locality in the Itapicuru River of Bahia state, Brazil. It sits in the small genus Erythrinus within the family Erythrinidae — the trahiras or wolf fishes — alongside the wider-ranging and better-known Erythrinus erythrinus, and in the same family as the much larger Hoplias and Hoplerythrinus. The Catalog of Fishes (Eschmeyer, California Academy of Sciences) recognises E. kessleri as a valid species distinct from E. erythrinus, though the genus has a history of taxonomic confusion and some specimens sold in the aquarium trade under the Erythrinus name are misidentified, including reports of fish labelled 'Erythrinus kessleri' that hobbyists suspect are actually undescribed Erythrinus forms from Peru or elsewhere.
The species epithet honours Karl Fedorovich Kessler (1815–1881), a Russian zoologist and ichthyologist. Because E. kessleri is restricted to a narrow set of Brazilian coastal drainages and rarely appears in the scientific literature, its biology is often extrapolated from its more widely distributed and studied relative E. erythrinus — a reasonable stand-in for genus-level traits, but not a substitute for direct data on this species.
Morphology
Like other trahiras, Erythrinus kessleri has an elongated, rounded-cylindrical body, a somewhat flattened head, and a large mouth armed with heavy, conical teeth suited to gripping and puncturing prey rather than slicing it. FishBase records a maximum published size of 7.5 in standard length, making it a comparatively small member of a family that includes true giants — the related Hoplias aimara can exceed a metre. As an obligate air-breather, it must periodically surface to gulp atmospheric air, a trait shared across Erythrinidae and tied to the low-oxygen backwaters and pools the family favours.
Colouration in trahiras generally runs from olive to brown with mottled or barred patterning that provides camouflage against submerged wood and leaf litter — consistent with an ambush predator that relies on stillness rather than pursuit. Detailed morphological description specific to E. kessleri beyond the type material is sparse in the available record.
Habitat
Erythrinus kessleri is known from coastal river drainages of Bahia state in northeastern Brazil, with its type locality in the Itapicuru River. It occupies freshwater habitats in the benthopelagic zone of tropical South American rivers — the kind of sluggish channels, backwaters and vegetated margins typical of trahiras generally, where low dissolved oxygen favours air-breathing fish.
Specific water chemistry data for wild populations of this species was not found in the available sources; care reports from the aquarium trade (discussed further below, and drawn partly from the better-documented congener E. erythrinus) suggest warm, tropical conditions are appropriate, but precise wild pH and hardness figures for E. kessleri specifically are not established in the record consulted here.
Feeding
Erythrinus kessleri is a piscivorous ambush predator, in keeping with the whole trahira family: it lies in wait among cover and strikes at anything that passes within range and fits in its mouth, rather than pursuing prey over distance. An aquarium care report on this species describes a captive individual fed frozen tilapia, shrimp and salmon, occasionally requiring live feeder fish to trigger a feeding response — and killing a tankmate pleco through sheer intimidation and predation pressure rather than active pursuit.
Its congener E. erythrinus is similarly described as an unfussy predator that readily takes meaty foods — whole fish, mussel and shrimp — and this genus-level pattern is a reasonable guide for E. kessleri. As with any predatory characin of this kind, any tankmate must be too large to be swallowed whole; there is no safe minimum size below that threshold.
Mating
No description of courtship or spawning behaviour specific to Erythrinus kessleri was found in the sources consulted. Several relatives within Erythrinidae — including species of Hoplias and Erythrinus — are substrate nest-spawners in which a pair (or a guarding male) selects and defends a pit or plant-associated nest site ahead of spawning, but whether this pattern has been documented for E. kessleri specifically is not established here, and this account does not extend that inference further than the genus level.
Breeding
As with mating behaviour, no direct account of captive or wild breeding in Erythrinus kessleri was found. Within the trahira family, several Hoplias and Erythrinus species are known as substrate nest-spawners in which the male guards a pit or a nest built among plants, defending the eggs and fry until they disperse — but many trahiras, including the smaller Erythrinus species, are only rarely bred in aquaria, and no aquarium-breeding reports for E. kessleri specifically were located. Prospective keepers should treat this species as essentially unbred in the hobby rather than assume the genus-typical mode has been demonstrated for it.
In the aquarium
Erythrinus kessleri should be kept as a solitary predator, not a community fish. One aquarium report on the species describes an individual reaching roughly 6–7 in after about a year, housed in a 40-gallon breeder tank, becoming increasingly solitary and intolerant of tankmates with age — including killing a pleco sharing its tank. Even at its modest maximum size of around 7.5 in, its mouth and teeth make it capable of taking down surprisingly large tankmates, and any fish sharing its tank must be too large to be swallowed and ideally not another slow-moving bottom-dweller likely to be targeted out of aggression rather than hunger.
Provide dense cover — driftwood, roots and plants — that lets the fish behave as the ambush predator it is, and because it is an obligate air-breather, ensure the tank has open access to the surface and is covered securely, as trahiras are strong, capable jumpers. Given the documented risk of misidentification in the trade (forum reports flag fish sold as 'E. kessleri' that may actually be undescribed Erythrinus forms from Peru or the so-called 'purple wolf'), buyers should treat the species label with some caution and be prepared for a genus-typical predatory temperament regardless of the exact identification.
Conservation
Erythrinus kessleri has not been formally assessed by the IUCN Red List and carries no conservation status (Not Evaluated). It is restricted to coastal river drainages of Bahia, Brazil, a region under ongoing pressure from agricultural development and habitat modification, but no species-specific population or threat data was found in the sources consulted here. Its narrow, poorly documented range is itself a reason for caution rather than complacency: data-sparse, geographically restricted freshwater fish in this part of Brazil are worth watching even in the absence of a formal assessment.