Taxonomy & naming
Hyphessobrycon acaciae was described by García-Alzate, Román-Valencia and Prada-Pedreros in 2010. The type specimen (holotype CZUT-IC 9308) is deposited at the Museo de Zoología of the Universidad del Tolima in Colombia. The type locality is a small tributary of the Río Aburrá in the department of Antioquia, placing it within the broader Magdalena River basin on the western slopes of the Cordillera Occidental. Eschmeyer's Catalog of Fishes records the valid name as Hyphessobrycon acaciae García-Alzate, Román-Valencia & Prada-Pedreros, 2010.
The genus Hyphessobrycon is one of the largest in the family Characidae, encompassing well over 150 valid species distributed across much of tropical and subtropical South and Central America. It is defined primarily by a combination of soft morphological characters — the presence of a humeral spot, fin ray counts, and the absence of an adipose spine — rather than by any single synapomorphy, and its boundaries have shifted repeatedly as molecular studies revise relationships within the broader characid radiation. H. acaciae fits the overall gestalt of the genus: small, laterally compressed, with a silver-red colour scheme typical of many Colombian stream tetras.
The specific epithet acaciae is noted in the Catalog of Fishes without detailed derivation in widely available sources; whether it refers to acacia vegetation at the type locality, a local toponym, or some other feature of the collection site has not been confirmed from accessible literature. The etymology should be regarded as uncertain pending consultation of the original description.
Morphology
H. acaciae is a micro-tetra, with FishBase recording a maximum standard length of 1 in. The body plan is the typical small Hyphessobrycon form: moderately deep, laterally compressed, with a rounded dorsal profile and the large eyes characteristic of miniaturised characids. Like most members of the genus it possesses an adipose fin, a small humeral spot, and fin-ray counts consistent with the broader Hyphessobrycon complex.
Detailed published colour notes for live specimens are sparse in accessible sources. In common with other small Colombian stream tetras the species is presumed to show a largely silvery base colour with reddish or orange pigment on the fins and possibly a faint lateral stripe, but asserting specifics beyond what the original description documents would be speculative. The species should be identified with care: at 1 in it falls within the size range of numerous sympatric or near-sympatric Hyphessobrycon from the Magdalena drainage, and misidentification in trade is plausible.
Habitat
The type locality and known distribution of H. acaciae lie within the Magdalena River system of Colombia, specifically in the foothill streams draining the Cordillera Occidental in Antioquia. The Magdalena basin is one of South America's most biodiverse river systems and harbours an exceptional diversity of small characids endemic to individual sub-catchments.
FishBase characterises the habitat as slow-flowing tributary streams with dense aquatic vegetation and leaf litter accumulation — conditions typical for small insectivorous tetras that forage among marginal cover and detrital substrate. Water in Andean foothill tributaries of this type is generally soft and acidic, with temperatures in the tropical lowland to foothill range. Seriously Fish reports a temperature window of 72–79 °F and a pH preference of 5.0–6.5 for this species, consistent with the soft, slightly tannin-stained water common to vegetated Colombian stream habitats. The restricted known range makes H. acaciae a potentially narrow-range endemic dependent on the integrity of a small number of stream catchments.
Feeding
H. acaciae is recorded as an insectivore in the wild, targeting small aquatic invertebrates typical of the stream-margin microhabitat: chironomid larvae, microcrustaceans, small worms, and invertebrate prey associated with leaf-litter and dense riparian vegetation. This feeding guild is characteristic of most small Hyphessobrycon from slow-flowing Neotropical streams.
In the aquarium, Seriously Fish notes that the species accepts a range of small live and dried foods, including Daphnia, Artemia nauplii, and high-quality micro-pellet or flake foods sized appropriately for a fish of 1 in. As with most micro-tetras, a varied diet that incorporates live or frozen invertebrate prey alongside prepared foods supports better colouration and reproductive condition. Feeding frequency should favour small, frequent offerings rather than large infrequent meals, as befits the feeding ecology of a small-bodied stream fish.
Mating
H. acaciae follows the egg-scattering, open-water spawning reproductive mode universal in Hyphessobrycon. Males are reportedly smaller than females (a reversal of the size dimorphism seen in some other tetras), and courtship likely follows the rapid chasing and lateral display behaviour typical of the genus, with males pursuing receptive females through vegetation.
Spawning is believed to occur among fine-leaved aquatic plants or over substrate, where adhesive eggs are scattered and left unattended by both parents. In the genus broadly, spawning activity is triggered by good feeding condition, slightly elevated temperature, and water changes that simulate rainfall. No specific courtship or mating observations for H. acaciae in the wild appear to be documented in accessible literature beyond what can be inferred from generic Hyphessobrycon biology.
Breeding
As a typical Hyphessobrycon, H. acaciae is presumed to scatter adhesive eggs among fine-leaved plants or spawning mops, with no parental care — adults will consume eggs given the opportunity and should be removed promptly after spawning. Seriously Fish records that eggs hatch in approximately 24–36 hours and fry become free-swimming within 3–4 days at typical breeding temperatures.
Conditioned adults should be maintained in soft, slightly acidic water consistent with the species' habitat profile (pH 5.0–6.5, 72–79 °F). A separate spawning tank densely planted with Java moss or fitted with a fine-mesh mop is standard practice. Fry are very small at free-swimming stage and require infusoria or commercial liquid fry food as a first food before graduating to freshly hatched brine shrimp nauplii. Detailed captive breeding accounts specific to H. acaciae are limited in hobbyist literature, reflecting the species' infrequent presence in trade.
In the aquarium
H. acaciae is a micro-tetra suited to a small, well-planted species or community aquarium. Seriously Fish describes it as a schooling community fish, and like most small Hyphessobrycon it should be kept in a group — a minimum of six individuals is recommended to encourage natural behaviour and reduce shyness, though larger schools of ten or more are preferable and show more confident, active behaviour.
Water chemistry should replicate the soft, acidic conditions of Colombian foothill streams: pH 5.0–6.5, temperature 72–79 °F, and low general hardness. Peat filtration or the use of botanicals (leaf litter, seed pods) to tannin-stain the water gently will produce conditions close to the natural habitat. Subdued lighting and dark substrate suit the species and display the colours well. Tankmates should be similarly small and peaceful; the fish's diminutive size (under 1 in) makes it incompatible with anything large enough to treat it as food, and it should not be mixed with vigorous or nippy species. Its rarity in the hobby means captive-bred stock is seldom available commercially, and the species remains primarily of interest to specialists in Neotropical micro-tetras.
Conservation
H. acaciae has not been formally assessed by the IUCN Red List as of 2026; its status is Not Evaluated (NE). The species is endemic to Colombia's Magdalena River drainage with a type locality in Antioquia, and its known distribution appears restricted to a small number of foothill stream catchments in the Cordillera Occidental. This restricted range, combined with the well-documented pressures on Andean Colombian freshwater habitats — agricultural land conversion, water extraction, sedimentation, and pollution in the Magdalena basin — suggests the species may warrant formal assessment.
The Magdalena basin has experienced severe historical deforestation and ongoing habitat degradation, and many of its endemic small fishes remain under-surveyed. Without formal assessment data, population trend information for H. acaciae is not available. It has attracted limited commercial aquarium trade interest, which reduces collecting pressure but also means that ex-situ conservation populations are not established. Any future IUCN assessment would need to resolve both the distributional limits and the degree of habitat modification within its known range.