Taxonomy & naming
Hemigrammus changae was formally described by Ota, Lima and Hidalgo in 2019, in a paper published in Zootaxa (volume 4577, issue 2, pages 335–347). The holotype — MUSM 663836, a specimen of 1 in SL — was collected on 9 December 2003 from Aguajal Cicra/Pozo Minero in the Madre de Dios department of Peru (12°33′48″S 70°07′03″W). The valid name is governed by Eschmeyer's Catalog of Fishes (Catalog of Fishes, CAS), which lists the authority as Ota, Lima & Hidalgo, 2019.
The genus Hemigrammus is one of the largest and most species-rich genera of small tetras in the family Characidae. H. changae belongs to a group of black-water stream specialists and can be distinguished from its congeners by a combination of characters: a wide dark horizontal stripe crossing the eye; an oval, horizontally elongated humeral blotch; a dark stripe along the base of the anal fin; the absence of a pseudotympanum; 6–7 gill rakers on the upper limb and 10–12 on the lower; and 34–35 vertebrae. It is sympatric with Hemigrammus lunatus in parts of its range, but the two species occupy distinct microhabitats — H. changae is characteristic of blackwater aguajales, whereas H. lunatus is more associated with white-water floodplain lakes.
The specific epithet honours the late Peruvian ichthyologist Fonchii Ingrid Chang Matzunaga (1963–1999), who made significant contributions to the study of Amazonian fishes before her untimely death.
Morphology
Hemigrammus changae is a slender, laterally compressed tetra with a maximum recorded standard length of 1.5 in. Like most members of the genus it has the typical characin body plan: a forked caudal fin, an adipose fin, and a laterally compressed profile that tapers from the deepest point behind the head to a narrow caudal peduncle.
The colour pattern in life is olive-grey along the dorsum, with a silvery head and abdomen. A narrow iridescent green midlateral stripe runs along the flank, and the fins are hyaline with a yellowish hue. The most diagnostic markings are a wide, bold dark stripe that passes horizontally through the eye, an oval humeral blotch positioned horizontally just behind the operculum, and a dark stripe that follows the base of the anal fin. These features distinguish H. changae from morphologically similar congeners in the same drainages.
Sexual dimorphism is subtle but present. Males, which attain a maximum of approximately 1 in SL, develop 7–11 small hooks on the anal-fin rays — a feature common to many characid males and used in species-level identification. Females grow somewhat larger, reaching upward of 1 in SL, and are generally deeper-bodied when gravid.
Habitat
The species is endemic to the upper río Madeira basin, specifically the río Madre de Dios and río Mamoré sub-basins in Peru and Bolivia. Within this region it is strongly associated with aguajales — seasonally and permanently flooded wetlands dominated by the buriti palm Mauritia flexuosa — where water is blackish, shallow, slow-flowing, and laden with decayed organic matter. This type of habitat is characteristic of the western Amazonian lowlands and produces the soft, acidic, tannin-stained water typical of blackwater systems.
H. changae is typically encountered in the shallow margins of these palm swamps, as well as in oxbow lakes and seasonal llanos streams of the same basin. The accumulation of decomposing leaf litter, submerged woody debris, and palm-frond detritus provides both shelter and a substrate for the microinvertebrates that form much of the diet. The species is documented from the Mamoré–Madre de Dios Piedmont ecoregion, a biogeographically distinct unit that bridges the Andean foothills and the Amazonian lowlands.
The aguajal habitat itself is spatially patchy and seasonally dynamic, expanding dramatically during the wet season flood pulse and contracting to isolated pools during the dry season. This patchiness may partly explain both the species' restricted distribution and its Vulnerable conservation status.
Feeding
No detailed dietary study of Hemigrammus changae has been published. Based on its habitat and the feeding ecology of closely related blackwater Hemigrammus species, it is inferred to be a micro-carnivore or omnivore, consuming small invertebrates — insect larvae, microcrustaceans, and zooplankton — gleaned from the water column and from the leaf-litter substrate, supplemented by organic detritus and small amounts of algae or plant matter.
In captivity, Hemigrammus tetras of similar size are generally undemanding feeders that accept a wide range of small prepared foods. High-quality fine flake, micro-pellets, and small frozen or live foods such as Daphnia, baby brine shrimp, and Cyclops are all appropriate. Variety in the diet supports good condition and breeding readiness; live and frozen items in particular are beneficial for blackwater species that may be less bold at feeding time in bright, sparsely furnished aquaria.
Mating
Hemigrammus changae has not been studied in detail in the context of reproductive behaviour. As a member of Hemigrammus and more broadly the egg-scattering characid assemblage, it is expected to follow the open spawning pattern typical of the group: males court receptive females with parallel swimming and fin-spreading displays, and spawning occurs in bursts with the pair driving into fine-leaved vegetation or submerged detritus.
Spawning stimuli in blackwater tetras commonly include a reduction in water conductivity simulating the onset of the rainy season flood pulse, a slight drop in temperature, and access to soft, acidic water. The male's anal-fin hooks, documented in H. changae, are consistent with the clasping behaviours described in other hook-bearing Hemigrammus during the spawning embrace, where the hooks may aid in brief contact between the pair during egg release.
Breeding
No captive breeding account specific to Hemigrammus changae appears in the available literature. Given its membership in Hemigrammus and its blackwater ecology, standard protocols for small Amazonian tetras are the logical starting point. Breeding aquaria are typically set up with very soft, acidic water (pH 5.5–6.5, near-zero hardness), warm temperatures (75–81 °F), dim lighting, and a layer of fine-leaved plants such as Java moss or spawning mops to catch the adhesive or semi-adhesive eggs.
Eggs are scattered in small numbers during each spawning pass and receive no parental care; adults should be removed after spawning to prevent egg predation. At warm temperatures eggs typically hatch within 24–48 hours and the fry become free-swimming after a further 2–3 days. First foods for the fry of small tetras are infusoria or commercial liquid fry foods, followed by freshly hatched Artemia nauplii once the fry are large enough. Because the species is rarely available in the trade, captive breeding records remain sparse.
In the aquarium
Hemigrammus changae is an obscure species in the aquarium hobby and is not commercially available through normal trade channels. Its blackwater aguajal habitat points to husbandry requirements similar to those of other soft-water Hemigrammus: soft, acidic, well-filtered water with low conductivity, warm temperatures in the 73–81 °F range, subdued lighting, and a heavily planted or leaf-littered aquascape that replicates the tannin-stained, structure-rich conditions of its native swamps. Indian almond leaves or alder cones can help condition the water and lower pH naturally.
As with most small characins, a group of six or more individuals is preferable to reduce any individual wariness and encourage natural schooling behaviour. Tankmates should be similarly diminutive and peaceful — other small blackwater tetras, dwarf cichlids such as Apistogramma, or small corydoras would be compatible. The species' small size (under 1.5 in SL) means it is vulnerable to being outcompeted by larger or more assertive fishes. Given how rarely it appears in the trade, any aquarist fortunate enough to obtain specimens should consider attempting captive breeding as a conservation contribution.
Conservation
Hemigrammus changae is assessed as Vulnerable (VU) on the IUCN Red List, under criterion B2ab(iii), based on an assessment conducted on 23 November 2020. The listing reflects a restricted area of occupancy within the Mamoré–Madre de Dios Piedmont ecoregion, combined with ongoing decline in the extent and quality of its aguajal wetland habitat. The principal threats identified are artisanal and small-scale gold mining in the Madre de Dios basin — one of the most heavily mined regions of the Peruvian Amazon — and deforestation driven by agricultural expansion and road-building, both of which degrade and fragment the palm-swamp habitats on which the species depends.
Because H. changae is confined to a specialised and spatially restricted habitat type, it has little capacity to shift range in response to local habitat loss. The Madre de Dios region has experienced severe deforestation and mercury contamination from mining in recent decades, and the longer-term outlook for intact aguajal systems in the basin remains uncertain. Effective conservation of this species is inseparable from the protection of the broader aguajal wetland complex and the regulatory controls on mining activity in the upper río Madeira catchment.