Taxonomy & naming
Hemigrammus matei was described by Carl H. Eigenmann in 1918. Eigenmann was the leading authority on South American characins of his era, and his monograph work produced descriptions of dozens of Hemigrammus species from across the continent. The valid name is recorded in Eschmeyer's Catalog of Fishes as Hemigrammus matei Eigenmann, 1918, with distribution given as South America: Argentina.
The species belongs to the large and taxonomically challenging genus Hemigrammus, a diverse assemblage of small tetras within the family Characidae. The genus lacks a single defining synapomorphy and has long been recognised as likely polyphyletic, meaning that relationships among its constituent species — and the boundaries of Hemigrammus itself — are still being resolved by molecular and morphological studies. The specific epithet matei is believed to honour Paul Matte (1854–1922), a German fish culturist and commercial aquarium-fish importer and breeder whose establishment was a significant conduit for tropical fish entering the European hobby in the late nineteenth and early twentieth centuries; type specimens appear to have come through his operation.
Morphology
Hemigrammus matei is a small, slender tetra reaching a maximum recorded total length of 1.5 in, based on data compiled by FishBase from the literature. Like other members of the genus it is laterally compressed and elongate, with the characteristic body plan of a small characid: a terminal mouth, a well-developed lateral line, and the adipose fin that defines the broader clade.
Detailed morphological data for this species — fin-ray counts, scale counts, precise colour pattern descriptions, and comparative meristic analysis — are not widely reported in accessible literature, reflecting the relatively sparse coverage the species has received since its description. FishBase notes a maximum pH tolerance of 7.8 and a hardness of up to 20 dH, suggesting the species tolerates neutral to slightly alkaline water, though these figures likely derive from limited observational data rather than comprehensive field studies.
Habitat
Hemigrammus matei is recorded from Argentina in South America. FishBase classifies the species as benthopelagic in subtropical freshwater, occupying the lower and mid water column of freshwater bodies. Beyond this, the precise type locality and the nature of the habitats it occupies — river channels, floodplain pools, vegetated shallows, or another microhabitat — are not well established in the available literature.
The subtropical freshwater classification implies seasonal temperature variation more pronounced than in tropical lowland systems, and the recorded temperature range of 72–79 °F is consistent with temperate-influenced river systems of southern South America. Water conditions on file from FishBase indicate a slightly alkaline tolerance (pH up to 7.8) and moderate hardness (up to 20 dH), which is consistent with many Argentinian river systems but should not be treated as a full characterisation of the species' habitat preferences in the absence of field data.
Feeding
No specific dietary studies appear to exist for Hemigrammus matei in the published or accessible literature. Diet is listed as unknown in FishBase. By analogy with other small Hemigrammus species, the species is likely a generalist micropredator and omnivore, feeding opportunistically on small invertebrates — insect larvae, microcrustaceans, zooplankton — and probably supplementing this with algae or plant material when animal prey is scarce.
In an aquarium setting, if the species were kept, it would almost certainly accept the standard small-tetra diet of quality flake food supplemented with small live or frozen foods such as Daphnia, brine shrimp nauplii, and finely ground dry foods. The lack of documented dietary information makes this species an example of the many nominal Hemigrammus taxa that have been described but remain essentially unknown ecologically.
Mating
No direct observations of mating behaviour in Hemigrammus matei have been published. Hemigrammus as a genus are egg-scattering open-water or plant-spawning tetras with no parental care, and H. matei almost certainly follows this pattern. Males typically develop slight sexual dimorphism in condition and, in some species, fin shape, while females become fuller-bodied when gravid.
In related Hemigrammus species, courtship involves males actively pursuing gravid females through fine-leaved vegetation or among plant stems, with spawning occurring in short bursts as the pair release small numbers of eggs that settle among the vegetation or substrate. No specific mating information is documented for this species.
Breeding
Hemigrammus matei has no published breeding account and is not known to be maintained in the aquarium hobby in any established way. Based on the biology of the genus, spawning would be expected to follow the typical small-tetra pattern: the pair scatter adhesive or semi-adhesive eggs among fine-leaved plants or over the substrate, after which the adults take no further interest in the eggs or fry.
Incubation in related species at comparable temperatures typically spans 24–36 hours, with fry becoming free-swimming within a few days and requiring very fine first foods — infusoria or commercial liquid fry food — before graduating to newly hatched brine shrimp. These generalisations are offered as reasonable inference from congener biology rather than documented fact for this species.
In the aquarium
Hemigrammus matei does not appear to be an established aquarium fish, and there are no husbandry accounts in the hobbyist literature reviewed for this profile. Its small size (1.5 in TL) and presumed hardiness relative to the subtropical water parameters on record suggest it would be manageable in a small to mid-sized community aquarium if it were available, but it is not offered in the trade in any regular or documented way.
If kept, the available water-parameter data suggest a temperature of 72–79 °F, a pH near neutral to slightly alkaline (up to 7.8), and moderate hardness (up to 20 dH) would be appropriate starting conditions. As with all small tetras, a planted aquarium with subdued lighting, peaceful tankmates of similar size, and a diet of varied small foods would represent best practice.
Conservation
Hemigrammus matei is assessed as Data Deficient (DD) on the IUCN Red List, with the assessment recorded from 30 September 2020. The DD designation reflects not an absence of concern but an absence of information: there is insufficient data on the species' distribution, population size, trends, or threats to assign it to a threat category. Its known range is limited to Argentina, and the precise locality of the original type specimens is not clearly documented.
Data Deficiency in a nominal species known from relatively few records is a common condition for South American characids described in the early twentieth century, many of which have not been the subject of subsequent field collection or taxonomic revision. Whether H. matei represents a genuinely rare and restricted taxon, a synonym of a more widespread species, or simply an under-collected fish from a poorly-surveyed part of Argentina cannot be determined from available data. Further field surveys and molecular work across the Characidae would help resolve its status.