Taxonomy & naming
Hemigrammus ulreyi was originally described by George Albert Boulenger in 1895 under the name Tetragonopterus ulreyi; the parenthetical authority in the current binomial reflects that transfer to Hemigrammus. Eschmeyer's Catalog of Fishes (Fricke, Eschmeyer & Fong) records the valid name as Hemigrammus ulreyi (Boulenger, 1895), with Tetragonopterus ulreyi Boulenger, 1895 as the basionym.
Within the family Characidae the genus Hemigrammus remains one of the largest and most species-rich tetra genera, and many of its members are in a state of taxonomic flux. Seriously Fish notes that H. ulreyi is currently treated as incertae sedis within Hemigrammus — a holding position reflecting the unsettled internal phylogeny of the genus rather than doubt about the species' validity. No junior synonyms are in widespread use, though GBIF lists Tetragonopterus ulreyi as the historical synonym.
Morphology
Hemigrammus ulreyi is a moderately elongate tetra reaching approximately 1.5–2 in total length, with Fishkeeper citing a maximum of around 2.5 in in well-fed adults. The body is laterally compressed and torpedo-shaped, typical of open-water characins, with the adipose fin and forked caudal fin characteristic of the family.
The most diagnostic feature is the lateral colour pattern from which the name Broken-Line Tetra derives: a dark, often iridescent mid-lateral stripe that does not run continuously from the operculum to the caudal peduncle but instead shows gaps or interruptions along its length. A pale or golden sheen overlies the upper flanks in good light, giving rise to the alternative name Goldentip Tetra recorded by GBIF. The body is otherwise silvery with a degree of translucency. Sexual differences are subtle; females in breeding condition are visibly deeper-bellied than males.
Habitat
The species is distributed through the Rio Paraguay basin, with records concentrated in Brazilian tributaries of that river system. The Paraguay is one of the principal tributaries of the Río de la Plata system, draining a vast lowland territory through Brazil, Bolivia, and Paraguay before joining the Paraná. Hemigrammus ulreyi inhabits slow-moving rivers, tributaries, and associated backwaters within this basin.
FishBase records the species' water parameters as pH 5.8–7.2 and hardness 0–10 dH, with temperatures of 73–81 °F, values consistent with the warm, soft-to-moderately-hard lowland waters of interior South America. Seriously Fish describes the habitat as slow-moving rivers and tributaries, suggesting marginal and vegetated zones rather than fast, open-channel water. The broad parameter range documented by different sources — Fishkeeper extends pH down to 5.0 — indicates a degree of tolerance across the soft-water spectrum typical of widely distributed South American characins.
Feeding
Hemigrammus ulreyi is an omnivore feeding on small invertebrates, organic particles, and plant matter in the wild. In the aquarium it accepts a wide range of prepared and live foods: quality flake and small granules form a practical staple, supplemented with frozen or live offerings such as bloodworm, Daphnia, brine shrimp, mosquito larvae, and similar small invertebrate foods. Seriously Fish and Fishkeeper both describe it as easy to feed, with no particular dietary demands.
As with most small tetras, conditioning on live and frozen foods improves breeding readiness and supports sustained colour. Feeding small portions two or three times daily is preferable to one large meal, keeping the fish active and reducing water quality impact in the aquarium.
Mating
Hemigrammus ulreyi is a typical characin egg-scatterer with no pair bond and no parental care. Courtship is brief and opportunistic: males chase females around the aquarium and between clumps of fine-leaved vegetation, driving the female to release eggs as the pair press close together. Spawning activity is most pronounced in the morning and can be triggered by slight drops in water temperature or a water change that mimics seasonal rainfall.
The species is best conditioned as a group; males compete loosely for access to gravid females, and the presence of rivals appears to sharpen display behaviour. Conditioning the group together on a varied diet with live and frozen foods over one to two weeks reliably brings females into visible spawning condition.
Breeding
Breeding Hemigrammus ulreyi follows the standard small-tetra protocol. A dedicated breeding tank of 10–15 US gal, bare-bottomed or with a mesh layer to protect eggs from being eaten, fitted with a clump of fine-leaved plants (Java moss, Cabomba, or synthetic spawning mops) and a small sponge filter, provides the essentials. Soft, slightly acidic water — pH around 6.0–6.5, hardness below 5 dH, temperature 75–79 °F — encourages spawning.
Eggs are scattered among plant leaves and substrate; Seriously Fish reports an incubation period of 24–36 hours at typical breeding temperatures, after which tiny fry hang near spawning medium for a further 24–36 hours before becoming free-swimming. Fishkeeper notes that the fry are light-sensitive in their earliest days and that the breeding tank benefits from subdued lighting initially. First foods are infusoria or commercial liquid fry food, progressing to newly hatched brine shrimp and micro-worm within a week. Adults show no parental care and will consume eggs and fry if not separated immediately after spawning.
In the aquarium
Hemigrammus ulreyi is a peaceful, active shoaling species and an easy community fish. Seriously Fish recommends keeping it in groups of six or more, ideally ten or above, which produces natural shoaling behaviour and the most confident, well-coloured fish. In smaller groups individuals can be skittish and the interrupted lateral stripe — the species' key feature — is often not displayed to advantage.
A planted community aquarium of 15 US gal or larger suits a group comfortably. Water should be soft to moderately hard and neutral to slightly acidic (pH 6.0–7.0; FishBase extends the range to 7.2 at the hard end), with temperature held at 73–81 °F. Good filtration and weekly partial water changes maintain the stable, low-nitrate conditions that keep these fish at their best. Suitable tankmates include other small, peaceful characins, dwarf cichlids, rasboras, and corydoras catfishes. The species poses no threat to invertebrates large enough not to fit in its mouth. It is a mid-water swimmer and leaves the upper and lower zones to appropriate tankmates.
Conservation
The IUCN Red List assessed Hemigrammus ulreyi as Least Concern (LC) on 4 March 2021 (assessor: F. Lima), reflecting the species' wide distribution across the Rio Paraguay basin and the absence of evidence of range-wide population decline. The Paraguay basin is one of South America's largest river systems, and the species occupies a broad range of slow-water habitats within it.
No specific conservation pressures have been flagged for this species at a range-wide level. Localised habitat degradation from agriculture, water abstraction, and sedimentation affects many lowland South American tributaries, but these pressures do not appear to threaten H. ulreyi as a whole at present. The ornamental trade relies on captive-bred stock for most supply, removing any meaningful collecting pressure on wild populations.