Taxonomy & naming
Moenkhausia tergimacula was described by Carlos Alberto Santos de Lucena and Zilda Margarete Seixas de Lucena in 1999, based on material collected from the upper Tocantins River basin near Minaçu, Goiás State, Brazil. The original description was published in Ichthyological Exploration of Freshwaters (volume 10, 1999). Eschmeyer's Catalog of Fishes records the valid name as Moenkhausia tergimacula Lucena & Lucena, 1999, with the authors not parenthesised — the species remains in the genus as originally placed.
Moenkhausia is one of the largest genera in the family Characidae, encompassing dozens of small to medium-sized tetras distributed broadly across South America, with particular diversity in the Orinoco and Amazon basins and their southern tributaries. M. tergimacula belongs to the upper Tocantins fauna, a stretch of the drainage now partly altered by hydroelectric impoundments, and its distribution spans Goiás, Pará, Tocantins, and Mato Grosso states in Brazil.
Morphology
Moenkhausia tergimacula is a small, moderately slender characid with a maximum recorded standard length of approximately 2 in. The body is compressed laterally in the typical tetra fashion, with the profile unremarkable for the genus: a rounded snout, relatively large eye, and the forked tail shared by most small characins.
The species epithet tergimacula — from Latin tergum (back) and macula (spot or blotch) — refers to the dorsal markings that characterise the species and help distinguish it from similar Moenkhausia. Beyond the eponymous dorsal spot pattern, detailed meristic and chromatic data remain sparsely published in the accessible literature; the original description in Ichthyological Exploration of Freshwaters is the primary morphological reference. FishBase records the species as benthopelagic, occupying the water column close to the substrate in freshwater tropical habitats.
Habitat
Moenkhausia tergimacula is endemic to the upper Tocantins River basin in central Brazil, with confirmed records from Goiás, Pará, Tocantins, and Mato Grosso states. The type locality is in the vicinity of Minaçu, Goiás — a region in the upper section of the Tocantins drainage that feeds one of the major river systems of the Brazilian Cerrado and Amazon transition zone.
The upper Tocantins flows through tropical freshwater habitats characterised by warm temperatures and moderate current; FishBase classifies the species as a tropical freshwater fish with a benthopelagic lifestyle, suggesting it forages near the substrate in riverine and associated habitats. The Cerrado biome, through which much of the upper Tocantins passes, is a biodiversity hotspot for freshwater fishes, and many of its endemic characids are associated with clear, seasonally variable streams and rivers over sandy or rocky substrates.
Feeding
FishBase assigns Moenkhausia tergimacula a trophic level of 3.3 (±0.5), placing it among omnivorous fishes that consume a mix of animal and plant material. This is consistent with the guild-level feeding ecology of most small Moenkhausia: opportunistic foragers taking small invertebrates, aquatic insect larvae, microcrustaceans, organic detritus, and plant matter as available.
In the aquarium, the species can be expected to accept the range of foods suitable for small omnivorous tetras — good-quality flake and micro-pellets, supplemented with frozen or live foods such as Daphnia, Artemia nauplii, or bloodworm. A varied diet is preferable to an exclusive prepared-food regime, supporting condition and colouration.
Mating
No dedicated observations of courtship behaviour in Moenkhausia tergimacula have been published in the accessible literature. The genus Moenkhausia broadly conforms to the egg-scattering strategy typical of small characids: males pursue females in active chases, and spawning occurs in bursts over fine-leaved vegetation or other suitable substrate, with adhesive or semi-adhesive eggs deposited among plant material. No parental care is provided by either sex.
In genera with comparable ecology, males in breeding condition are often slightly slimmer and more intensely coloured than females, and spawning activity is typically triggered by warmer temperatures, frequent water changes, and the presence of suitable egg-laying sites. These generalisations apply provisionally to M. tergimacula pending direct observation.
Breeding
Dedicated breeding accounts for Moenkhausia tergimacula in captivity are absent from the available literature. Based on the broad reproductive pattern of the genus and of small Characidae generally, the species is expected to be an egg-scatterer producing adhesive eggs among fine-leaved aquatic plants or spawning mops, with no parental care — the standard approach for the family.
Conditioned adults would likely spawn over spawning mops or dense plant growth, producing small adhesive eggs that should be separated from the adults to prevent predation. Incubation at tropical temperatures typically takes 24–48 hours for small characids, with free-swimming fry requiring infusoria or commercial liquid fry food as a first food before graduating to newly hatched brine shrimp. Data specific to this species remain sparse in the hobbyist and scientific literature.
In the aquarium
Moenkhausia tergimacula is not a commonly traded tetra and is lightly represented in hobbyist literature, though its small size and omnivorous temperament make it manageable for aquarists experienced with small South American characids. Like most Moenkhausia, it would be best kept in a school of six or more individuals in a well-planted aquarium with open swimming space and subdued to moderate lighting.
Water parameters appropriate for upper Tocantins species would include warm temperatures (approximately 75–82 °F), near-neutral to slightly acidic pH, and soft to moderately hard water, though precise husbandry data for this species specifically are not established in the published aquarium literature. Peaceful community tankmates of similar size — small tetras, rasboras, or Corydoras catfishes — would be suitable companions. Given the species' restricted range and benthopelagic habit, a substrate of fine sand with leaf litter would reflect its natural environment.
Conservation
Moenkhausia tergimacula is assessed as Least Concern (LC) on the IUCN Red List, with the assessment confirmed as of November 2018 via FishBase. The LC listing reflects the absence of evidence for range-wide population decline sufficient to trigger a threatened category, though the species is endemic to Brazil and its range, centred on the upper Tocantins basin, overlaps with a drainage system that has been substantially modified by hydroelectric development — most notably the Serra da Mesa reservoir in Goiás, which inundated significant stretches of the upper Tocantins River.
The long-term impact of these impoundments on the populations and distribution of endemic upper Tocantins characids, including M. tergimacula, warrants monitoring. FishBase records the species as having high resilience to fishing pressure, which, combined with its small size and omnivorous diet, provides some buffer against localised habitat disturbance. It is not known to be a target of the ornamental fish trade at commercial scale.