Taxonomy & naming
Hasemania melanura was described by Max Ellis in 1911, with the type locality in the Rio de Janeiro drainage of southeastern Brazil. The species has sat in the genus Hasemania since its description, a small group of Atlantic Forest characins in the family Characidae that share a distinctive combination of characters including the absence of the adipose fin — unusual within Characidae — and a reflective silver or white tipping to the fin margins that gives rise to common names such as 'silvertip tetra' or 'silver-tip tetra'.
Eschmeyer's Catalog of Fishes (Fricke, Eschmeyer & Fong) recognises Hasemania melanura Ellis, 1911 as the valid name. The genus Hasemania is small, with only a handful of described species, all endemic to coastal Atlantic Forest river systems in Brazil. Within Characidae the genus belongs to the speciose subfamily Stevardiinae by some treatments, though tribal placement of Hasemania has been revised as molecular phylogenies have reshaped the family's internal classification; the genus has historically also been associated with Tetragonopterinae in the older literature. The common name 'black-band tetra' references the dark lateral stripe that runs the length of the body.
Morphology
Hasemania melanura is a slender, moderately compressed tetra reaching a maximum standard length of roughly 1.5–2 in. The body is typical for a small stream characin: a torpedo-shaped profile tapering to a forked tail, the snout blunt, and the mouth small and terminal. One of the genus's distinguishing characters is the complete absence of the adipose fin, the small fleshy fin between the dorsal and caudal that is otherwise near-universal in Characidae.
Colouration in adult males is the species' most striking attribute. The flanks carry a bold, dark lateral band that runs from behind the gill cover to the base of the caudal fin — the 'melanura' (meaning 'black tail') element. Against this dark stripe the fin tips gleam with a brilliant white or silver iridescence, most vivid on the dorsal, caudal, and anal fins. Females are plumper-bodied, particularly when gravid, and their fin-tip silver is somewhat subdued compared with displaying males. In both sexes the iridescence is intensified under good lighting and by diet, and can appear gold-tinged in certain light conditions.
Habitat
Hasemania melanura is endemic to the coastal Atlantic Forest river drainages of Rio de Janeiro state in southeastern Brazil — a region characterised by short, fast-draining rivers that descend from the Serra do Mar mountains to the Atlantic coast. These streams flow through remnant Atlantic Forest, one of the world's most biodiverse and most threatened tropical biomes, and carry soft, acidic water heavily stained by tannins leaching from leaf litter and submerged wood.
Reported water conditions reflect this blackwater origin: pH values in the range of approximately 4.5–6.5, temperatures broadly in the 72–81 °F range, and very soft, low-conductivity water with little dissolved mineral content. The fish typically inhabits slower marginal sections and pools of these streams, where leaf litter accumulates, submerged roots and branches provide cover, and fine-leaved aquatic vegetation may be present. Its subtropical to warm-temperate distribution — Rio de Janeiro sits at roughly 23 °S — means the species experiences seasonal temperature variation in the wild, and tolerates cooler conditions better than many Amazon basin tetras.
Feeding
Like most small characins, Hasemania melanura is an opportunistic omnivore. In its natural Atlantic Forest streams the diet likely encompasses small aquatic invertebrates, micro-crustaceans, insect larvae, and organic detritus — whatever small prey items are available in the leaf-litter microhabitat.
In the aquarium the species accepts a wide range of foods without difficulty. High-quality small flake or micro-pellets form a practical staple, and conditioning for colour and breeding benefits noticeably from regular supplementation with small live or frozen foods: micro-worms, newly hatched brine shrimp nauplii, Daphnia, and Cyclops all suit its small mouth well. Bloodworm can be offered in moderation. Multiple small feedings rather than one large daily meal suit the species' continuous grazing habits.
Mating
Hasemania melanura is an egg-scattering, open spawner with no parental care — a reproductive strategy typical of small, schooling characins. In a well-maintained group, males can be seen displaying to females: spreading their fins to show the silver tipping to best advantage, shimmering alongside receptive females and manoeuvring into position for the brief spawning embrace.
Spawning readiness in males is signalled by intensified colouration and fin display, while ripe females become visibly plumper in the ventral region. In a community setting courtship behaviour is continuous at low intensity within the school; in a dedicated breeding setup it becomes more focused once the fish are conditioned. The spawning act itself is a rapid, rolling embrace in which eggs and milt are released simultaneously among fine-leaved vegetation or substrate.
Breeding
Breeding Hasemania melanura in captivity follows the standard approach for small egg-scattering characins. A separate, small breeding tank — 10–15 US gal — is useful to prevent egg predation by the parents, who show no parental instinct and will actively consume their own spawn. The tank should be dimly lit and fitted with a generous quantity of fine-leaved plants (Java moss, Cabomba, or synthetic spawning mops work well) to give eggs somewhere to fall and stick and to disperse the parents so they cannot simply hoover up every egg.
Water chemistry should mirror the species' acidic, soft-water origins: pH in the 5.5–6.5 range, very soft (low GH and KH), and temperatures in the 75–79 °F range. Conditioning a small group on live and frozen foods for a week or two before the breeding attempt improves egg production and fertilisation rates. Eggs are small and adhesive, scattered loosely over the spawning medium. Adults should be removed promptly once spawning ceases, as they will eat any eggs they find. At typical breeding temperatures the eggs hatch within 24–36 hours and the tiny fry become free-swimming a few days later, at which point they need very fine first foods — infusoria or commercial liquid fry food — graduating to newly hatched brine shrimp nauplii as they grow.
In the aquarium
Hasemania melanura is a hardy, adaptable tetra well suited to an intermediate hobbyist. It does best in groups of six or more, which suppress individual timidity and bring out the natural schooling and display behaviour that makes the species attractive. A tank of 15 US gal or more provides adequate space for a proper school and the swimming room the species needs; a longer footprint is preferable to a tall, narrow aquarium.
Water chemistry should lean toward the soft and acidic — pH 5.5–7.0, soft to moderately soft — reflecting the Atlantic Forest blackwater origin, though the species adapts to moderately harder water without difficulty in practice. Temperature flexibility is one of its assets: the subtropical latitude of its homeland means it tolerates a range from roughly 72 °F to 81 °F, and can be kept at the cooler end in an unheated room in mild climates. A planted setup with subdued areas, leaf litter or driftwood for tannin release and visual complexity, and open mid-water swimming space suits it ideally; under such conditions the silver-tipped fins catch the light and the species shows at its best. It is a peaceful community fish compatible with similarly sized small tetras, rasboras, Corydoras, and dwarf cichlids that share its soft-water preferences.
Conservation
Hasemania melanura has not been formally assessed on the IUCN Red List as of the time of writing, and carries a status of Not Evaluated (NE). The absence of a formal assessment does not, however, mean the species is without conservation concern. It is endemic to the coastal Atlantic Forest drainages of Rio de Janeiro state — a river system within one of the world's most fragmented and pressured biomes.
The Atlantic Forest of southeastern Brazil has been reduced to well under 15 percent of its original extent by centuries of deforestation, agricultural conversion, and, in the Rio de Janeiro region, intense urbanisation. Stream habitats within these catchments face pollution from urban runoff, sedimentation, and direct channel modification. A species with a restricted, endemic distribution in a heavily urbanised catchment is inherently vulnerable to these pressures even without the quantitative population data needed for a formal Red List assessment. Most Hasemania melanura in the hobby is likely captive-bred, given the species' long history in the trade, which reduces collection pressure on any remaining wild populations.