Taxonomy & naming
Hemigrammus machadoi was described by Ota, Lima & Pavanelli in 2014 from material collected in the Rio Madeira and Rio Paraguai basins of Mato Grosso and Rondônia, Brazil. The original description also included a redescription of the related Hemigrammus lunatus. Hemigrammus Gill, 1858, remains one of the largest and most species-rich characid genera in the Neotropics, a grade of small, laterally compressed tetras united largely by the presence of scales on the caudal fin base rather than by exclusive synapomorphies.
Eschmeyer's Catalog of Fishes records the valid name as Hemigrammus machadoi Ota, Lima & Pavanelli, 2014. No synonyms are presently recorded, and the species has remained in its original generic placement since description.
Morphology
Hemigrammus machadoi is a small, slender tetra with a maximum recorded standard length of 1.5 in. As with most Hemigrammus, the body is moderately compressed laterally and the caudal fin base bears a covering of small scales — the character that historically distinguished the genus from Moenkhausia and the scaleless-caudal Hyphessobrycon.
Detailed meristic and morphometric data are provided in the original description. Like other small members of the genus, it is presumed to carry the typical characid complement of paired fins, an adipose fin, and a forked caudal; specific colour pattern details distinguishing it from congeners are elaborated in the original description and are the primary characters used in field and laboratory identification.
Habitat
The species occupies slow-flowing, low-gradient streams and small rivers with clear to slightly dark-stained waters in the Brazilian states of Mato Grosso and Rondônia. Recorded drainages include the Mamoré, Guaporé, and middle-to-lower Madeira (Rio Madeira basin) as well as the Upper Paraguay and Paraná-Paraguay systems — making it one of a small number of species documented across multiple major South American river basins.
Water conditions recorded by FishBase for collection sites approximate a pH near 7 and a temperature of around 77 °F (77 °F), consistent with the warm, near-neutral terra firme streams typical of western Mato Grosso and Rondônia. Its multi-basin distribution is unusual within the Hemigrammus fauna of the Upper Paraguay region.
Feeding
No dedicated dietary study is available for Hemigrammus machadoi in the published literature. Like most small Hemigrammus species it is likely an opportunistic omnivore, consuming small invertebrates — insect larvae, microcrustaceans, and surface-fallen insects — alongside algae and plant material, in line with the generalised feeding ecology documented across the genus.
In the aquarium, members of this size class adapt readily to fine-particulate prepared foods (micro-pellets, quality flake), supplemented with small live or frozen foods such as baby brine shrimp, Daphnia, and Cyclops to maintain condition and colour.
Mating
No detailed observations of courtship behaviour in Hemigrammus machadoi have been published. Based on the broader reproductive biology of Hemigrammus, the species is expected to be an egg-scattering open spawner with no parental care. Males in spawning condition typically pursue females into fine-leaved vegetation or near substrate, where eggs are scattered and left to develop unattended.
Adhesive eggs are typical in many Hemigrammus species, attaching loosely among plant matter or settling to the substrate. Adults show no pair bonding and will readily consume eggs after spawning.
Breeding
No captive-breeding account specific to Hemigrammus machadoi appears in the published or hobbyist literature to date. Given its small size and general affinity with the genus, standard Hemigrammus breeding methods are likely applicable: a separate, densely planted spawning tank with soft, slightly acidic to neutral water, fine-leaved plants or spawning mops, and removal of adults immediately after spawning to prevent egg predation.
Eggs of most small Hemigrammus hatch within 24–36 hours at typical tropical temperatures; fry are free-swimming a few days later and initially require infusoria-grade first foods before accepting newly hatched brine shrimp nauplii. Data sparse for this species specifically.
In the aquarium
Hemigrammus machadoi is rarely encountered in the ornamental fish trade and is not a commonly kept species as of 2024. Given its ecology — small, schooling, from slow-moving warm streams — it would be best maintained in a group in a well-planted aquarium with gentle filtration, a dark substrate, and subdued or dappled lighting to approximate its natural habitat.
Water parameters should target near-neutral pH (around 6.8–7.2) and a temperature in the mid-20s Celsius (75–79 °F / 75–79 °F), matching FishBase records for its collection localities. As a small species reaching only 1.5 in SL, it is suitable for modestly sized aquaria and is unlikely to be aggressive toward similarly sized tankmates.
Conservation
Hemigrammus machadoi was assessed by the IUCN Red List in November 2018 and placed in the Least Concern category, reflecting its known occurrence across multiple river basins in Brazil (Rio Madeira, Mamoré, Guaporé, and the Paraná-Paraguay system). Its multi-basin distribution reduces localised extinction risk compared to narrowly endemic Hemigrammus species.
No specific threats are listed in the IUCN assessment. Ongoing pressures in Mato Grosso and Rondônia — including agricultural expansion, deforestation, and associated water-quality changes in the Cerrado-Amazon transition zone — are relevant to the long-term status of stream-dwelling characids across the region, but the species' broad distribution currently buffers it against these pressures.