Taxonomy & naming
Hemigrammus melogrammus was described by Carl H. Eigenmann in 1908. The Catalog of Fishes (Eschmeyer, Fricke & van der Laan) records the valid name as Hemigrammus melogrammus (Eigenmann, 1908); the parenthetical authority indicates it was placed in a different genus at original description before being referred to Hemigrammus.
Hemigrammus Gill, 1858 is one of the largest genera in the family Characidae and encompasses dozens of small, schooling tetras broadly distributed across tropical South America. The genus is diagnosed primarily by the presence of scales on the caudal fin base, a character that separates it from the closely related Hyphessobrycon. Within Hemigrammus, species boundaries and relationships remain an active area of research, and the genus as currently constituted is likely polyphyletic.
No common names have been established for H. melogrammus in the English-language hobby or scientific literature.
Morphology
Hemigrammus melogrammus reaches a maximum recorded standard length of approximately 1.5 in, placing it among the smaller members of its genus. It shares the compressed, fusiform body plan typical of the group: a moderately deep body, a forked caudal fin, and the adipose fin present between the dorsal and caudal that characterises most characins.
Detailed colour pattern data for this species in life is sparse in the published literature. As with many Hemigrammus species, it presumably carries some combination of a lateral stripe, a caudal spot, and silvery-to-translucent flanks typical of the genus, but precise pigmentation descriptions from the original account or subsequent revisions are not available in the sources consulted here. Aquarists and researchers should treat any unverified colour descriptions of this species with caution.
Habitat
Hemigrammus melogrammus is native to the upper Amazon basin of South America. FishBase records the species as benthopelagic, inhabiting freshwater environments in the tropical zone.
The upper Amazon and its tributaries encompass a broad range of water types, from clear, rocky highland streams to tannin-stained blackwater forest creeks. FishBase records water parameters for this species as pH 5.8–6.8 and temperature 73–81 °F (73–81 °F), consistent with the soft, warm, acidic conditions typical of Amazonian Hemigrammus. The precise localities and river systems within the upper Amazon where H. melogrammus has been collected are not documented in detail in the sources available.
Feeding
No species-specific feeding data has been published for Hemigrammus melogrammus. By analogy with thoroughly studied congeners, the species is presumed to be a micropredator and opportunistic omnivore in the wild, consuming small invertebrates — insect larvae, microcrustaceans, and zooplankton — as well as algae and fine plant material, as is characteristic of most small Amazonian characins.
In the aquarium, members of this genus are typically undemanding and accept good-quality dried foods including flake and micro-pellets, supplemented by small frozen or live foods such as Daphnia, brine shrimp nauplii, and cyclops. A varied diet supports condition and, where sexual dimorphism is expressed, colour.
Mating
Specific observations of mating behaviour in Hemigrammus melogrammus have not been published in the accessible literature. The species almost certainly follows the general Hemigrammus reproductive strategy: egg-scattering open spawning with no pair bond and no parental care, a strategy shared by the vast majority of characins.
Males in breeding condition in related species typically become more intensely coloured and pursue females through fine-leaved vegetation or other spawning substrate. Spawning occurs when a male draws alongside a receptive female and both scatter and fertilise eggs simultaneously. The adhesive eggs settle among plants or substrate; adults do not attend them and will eat any eggs they encounter.
Breeding
No breeding records specific to Hemigrammus melogrammus in captivity have been located. Based on the well-documented biology of closely related species in the genus, it can be inferred that successful breeding would require soft, acidic water in the range of pH 5.8–6.8 at temperatures around 77–81 °F (77–81 °F), with fine-leaved plants or a synthetic spawning mop to receive the adhesive eggs.
Incubation in similar Hemigrammus species typically runs 24–36 hours at tropical temperatures, with fry becoming free-swimming and needing very fine first foods within a few days. Adults should be removed after spawning to prevent egg predation. The species is not known to be available in the trade, so captive breeding records are essentially absent.
In the aquarium
Hemigrammus melogrammus is not established in the ornamental fish trade and is unlikely to be encountered by hobbyists outside of specialist collections or importations of wild-caught mixed tetra shipments from the upper Amazon. General Hemigrammus husbandry principles would apply: a well-planted aquarium with soft, slightly acidic water (pH 5.8–6.8, 73–81 °F / 73–81 °F), subdued or filtered lighting, dark substrate, and a group of at least six to eight individuals to allow natural schooling behaviour.
The species' small size makes it suitable for a community of similarly sized, peaceful fish. Tankmates from similar soft-water habitats — other small Hemigrammus, pencilfish, small rasboras, or dwarf cichlids such as Apistogramma — would be appropriate. Water quality should be maintained with regular changes; small tetras from soft, dilute Amazonian waters are intolerant of accumulated nitrates and hardness.
Conservation
Hemigrammus melogrammus is assessed as Least Concern (LC) on the IUCN Red List, with the most recent assessment dated 2021. The Least Concern designation indicates that, based on available information, the species does not meet the thresholds for a threatened category. It is distributed within the upper Amazon basin, a vast river system that, while subject to ongoing deforestation, agricultural encroachment, and pollution pressures in parts, still retains large areas of intact habitat.
The relative obscurity of H. melogrammus and its absence from the ornamental trade mean that collection pressure is not a documented concern. As with most small, range-restricted Amazonian fishes, the principal long-term threats are habitat loss from land clearance and changes to hydrological regimes within its native river system.