Taxonomy & naming
Acestrocephalus anomalus was originally described as Xiphorhamphus anomalus by Franz Steindachner in 1880. The species was subsequently moved to the genus Acestrocephalus, and the parenthetical authority reflects that transfer. Menezes (1976) provided a detailed redescription of the species, and the type series includes specimen NMW 57983 held at the Naturhistorisches Museum Wien. Eschmeyer's Catalog of Fishes records the type designation as by original designation, with Xiphorhamphus anomalus Steindachner, 1880 as the type species of the genus concept to which it was originally referred.
The genus Acestrocephalus belongs to the family Characidae, the large and diverse New World characid radiation. The genus is characterised by its predatory dentition and elongate body form. Vari et al. list Acestrocephalus anomalus in the Smithsonian checklist of freshwater fishes of Colombia as a confirmed endemic of the Magdalena River basin, one of the country's major trans-Andean drainages.
Morphology
Acestrocephalus anomalus reaches a maximum recorded standard length of 8 in, making it a sizeable member of its genus. The fish is elongate and laterally compressed in the manner of a pursuit predator, adapted for rapid acceleration in flowing-water habitats.
The species' most diagnostic character — and the probable inspiration for its name — is a second row of teeth on the anterior portion of the lower jaw (dentary), an arrangement described as anomalous relative to related taxa. The ETYFish Project notes that the epithet anomalus, Latin for odd or irregular, most likely alludes to this unusual dental feature, though Steindachner did not make the allusion explicit in the original description. Detailed colour pattern data for wild-caught individuals are sparse in the available literature.
Habitat
Acestrocephalus anomalus is documented from the Magdalena River basin of Colombia, where it occupies freshwater, benthopelagic, tropical environments. The Magdalena is Colombia's principal trans-Andean river, draining a large inter-Andean valley before entering the Caribbean Sea, and it supports a high degree of ichthyological endemism.
Restrepo-Santamaria et al. record Acestrocephalus anomalus from river channel habitats in Caribbean river basins of northwestern South America, consistent with an association with flowing-water conditions in the Magdalena system. Precise microhabitat data — substrate preference, depth range, riparian associations — are not available in the published sources reviewed for this account.
Feeding
FishBase records a trophic level of 3.9 (±0.6 se) for Acestrocephalus anomalus, placing it firmly in the predator/carnivore guild above the general omnivore baseline of roughly 2.0. A trophic level approaching 4.0 is consistent with a diet dominated by smaller fishes and larger invertebrates rather than detritus, algae, or plankton.
Beyond the trophic level estimate, detailed dietary data for this species in the wild are sparse. Based on its body form, dentition, and the feeding ecology of related Acestrocephalus species, it is reasonable to infer a diet of small fishes and aquatic invertebrates, but this inference should not be taken as documented field data.
Mating
Specific mating observations for Acestrocephalus anomalus have not been reported in the sources available for this account. Characids of this body size and predatory habit are generally presumed to be egg-scattering open spawners with no parental care, in line with the broad characid reproductive pattern, but published mating data for this species are absent.
Field studies on reproduction in the Magdalena ichthyofauna are limited, and the IUCN Data Deficient listing for this species reflects the general scarcity of biological documentation. Any account of courtship or seasonal spawning triggers would require directed fieldwork in the Magdalena system.
Breeding
No captive breeding records for Acestrocephalus anomalus appear in the literature reviewed for this account, and the species is not reported in the ornamental fish trade. Published data on egg characteristics, incubation period, fry development, or rearing requirements are absent.
By analogy with other characids of similar size, spawning would likely involve egg scattering without parental care, with adhesive or semi-adhesive eggs deposited among fine-leaved vegetation or submerged structure. This is inference rather than documented observation; data sparse.
In the aquarium
Acestrocephalus anomalus is not an established aquarium species and is not reported in the hobbyist literature. Its maximum size of 8 in, predatory trophic level, and origin in flowing Magdalena River habitat suggest it would require a large, well-filtered aquarium with good current if ever kept. Its dentition and predatory habits would likely make it incompatible with smaller tank companions.
In the absence of any husbandry record, specific care parameters cannot be responsibly stated. Aquarists with a specialist interest in South American characid predators may find the species of taxonomic interest, but it is not available through ordinary ornamental trade channels and no captive-maintenance notes exist in the sources reviewed.
Conservation
The IUCN Red List assessed Acestrocephalus anomalus as Data Deficient (DD) on 8 October 2014. The Data Deficient category reflects a genuine lack of information on the species' population size, trends, and threats rather than a determination that the species is secure. A narrowly endemic fish confined to the Magdalena River basin — itself subject to ongoing deforestation, agricultural runoff, and hydroelectric development — may face significant pressures that are simply undocumented.
The Magdalena basin supports high levels of freshwater fish endemism, and many of its species remain incompletely surveyed. A reassessment of Acestrocephalus anomalus would benefit from population surveys, range verification, and basic natural history documentation. Until such data exist, the species' true conservation position remains unknown.