Taxonomy & naming
Hemigrammopetersius major was originally described by the Belgian ichthyologist George Albert Boulenger in 1903, hence the parenthetical authority — the species has been moved at least once from its original genus placement since description. The valid name is governed by Eschmeyer's Catalog of Fishes (Fricke, Eschmeyer & Fong), which places it in Phenacogrammus, a genus of African tetras in the family Alestidae.
The family Alestidae — sometimes called African characins — encompasses the diverse tetra-like fishes of sub-Saharan Africa, including the giant tigerfish (Hydrocynus) at one extreme and the small, jewel-like Congo tetras (Phenacogrammus) at the other. Within Alestidae, Phenacogrammus is characterised by a moderately deep, compressed body, an adipose fin, and the distinctive finnage of larger species. Hemigrammopetersius major is the largest commonly referenced species in the genus, the specific epithet major (Latin: larger, greater) directly referencing its size relative to congeners.
This fish was long listed as Phenacogrammus major; Eschmeyer's Catalog of Fishes places the species in Hemigrammopetersius, and the current combination Hemigrammopetersius major is followed here.
Morphology
FishBase records a maximum standard length of 3.7 in for Hemigrammopetersius major, making it one of the larger Phenacogrammus species. Like other members of the genus it has the compressed, deep-ish body typical of alestid tetras, with an adipose fin between the dorsal and the deeply forked caudal. The scales are relatively large and reflective, giving the flanks a silvery or faintly iridescent appearance in good light.
Detailed morphological data for this species in the published literature is sparse in accessible sources. The genus is characterised by a terminal or slightly upturned mouth suited to mid-water feeding, and in the larger species the male's median fins — dorsal and caudal lobes in particular — tend to develop extended rays, though whether H. major exhibits this trait as strongly as its congener P. interruptus is not confirmed from available cache data.
Habitat
Hemigrammopetersius major is distributed across several river basins in Cameroon and in Rio Muni (the mainland portion of Equatorial Guinea). FishBase records its presence in the Dja River (part of the Sangha drainage feeding the middle Congo basin), the Nyong, Ntem, and Sanaga river systems — all rivers that drain west and south through the Atlantic Congo forest zone.
These are predominantly lowland to sub-montane forest rivers characterised by soft, warm, often tea-coloured water rich in dissolved organic matter from leaf litter and vegetation. Current varies from slow backwaters and forest pools to moderate main-channel flow. Precise water-chemistry parameters for the species' natural range are not captured in the available cache data, but the broader Cameroon forest river zone typically yields soft, mildly acidic water with conductivities well below 100 µS/cm and temperatures in the 73–81 °F range.
Feeding
Like other alestid tetras, Hemigrammopetersius major is an omnivore that forages opportunistically in the water column and at the surface. The natural diet of forest-river tetras in this genus typically includes small invertebrates — aquatic insect larvae, small crustaceans, and terrestrial insects falling onto the water surface — as well as algae and plant detritus.
In captivity, Phenacogrammus species accept a broad range of prepared and live foods. High-quality flake and micropellet foods provide the nutritional base, while regular supplements of frozen or live Daphnia, bloodworm, Artemia, and similar invertebrates improve condition and coloration. Given the species' size, it can handle larger food items than the smallest tetras, and a varied diet is advisable to replicate the breadth of its natural foraging.
Mating
Hemigrammopetersius major is presumed to follow the reproductive strategy typical of the genus: open-water egg-scattering with no parental care. In related Phenacogrammus species, males develop elongated fin rays and engage in displays toward females, with spawning occurring over fine-leaved vegetation or in open water.
Specific behavioural observations for H. major in captivity are not documented in available sources. Based on congener biology, males are likely to be the more ornamented sex, using fin displays to court females, and spawning is likely to be triggered by water changes or a slight temperature increase simulating the onset of the rainy season — a common cue for Central African forest tetras.
Breeding
No captive breeding accounts specific to Hemigrammopetersius major are recorded in the available cache data. By analogy with the closely related P. interruptus and other alestid tetras, the species is expected to be an egg-scatterer that deposits non-adhesive or weakly adhesive eggs among fine-leaved plants or over open substrate, with the adults offering no parental care and readily consuming their own spawn.
Breeders working with congeners typically use slightly soft, warm water, condition adults on live and frozen foods, and perform a partial water change to stimulate spawning. Eggs hatch within 24–48 hours at tropical temperatures, and the tiny fry require infusoria or commercial liquid fry food as a first food before graduating to nauplii. Given the species' rarity in the hobby, documented captive-breeding protocols remain sparse.
In the aquarium
Hemigrammopetersius major is rarely seen in the aquarium trade; it is far overshadowed by its smaller, vividly iridescent congener, the Congo tetra (P. interruptus). When available, it would suit a spacious, well-planted aquarium with soft to moderately soft, warm water in keeping with its Cameroonian forest-river origins. Its size — approaching 3.9 in — means it needs more room than the smaller alestids and is best housed with similarly sized, peaceful companions.
Being a schooling species, a group of six or more would allow natural social behaviour and reduce individual stress. Subdued lighting, a dark substrate, and some surface shade from floating plants help replicate forest-stream conditions and bring out whatever iridescence the flanks carry. The species is data-sparse in hobby literature, so keepers would be drawing significantly on experience with P. interruptus and other large alestids to guide care.
Conservation
Hemigrammopetersius major has not been assessed by the IUCN Red List; FishBase records it as Not Evaluated (NE). No conservation data — population estimates, threat assessments, or trade-volume figures — are available in the sources cached for this article.
The species is distributed across several river basins in Cameroon and Equatorial Guinea, a region subject to deforestation, artisanal mining, and expanding agricultural conversion of riparian forest. While the multi-basin distribution provides somewhat more security than a narrow-range endemic, the health of Central African forest rivers is generally under increasing pressure. Until a formal IUCN assessment is completed, the species' status remains unknown.