Taxonomy & naming
Moenkhausia iris was formally described by Manoela Marinho and Fernando Dagosta in 2023, in a paper published in the Journal of Fish Biology (vol. 103, no. 5, pp. 1122–1128; DOI: 10.1111/jfb.15513). The type locality is the rio Galera at Chapada dos Parecis in the upper rio Guaporé drainage, itself a tributary of the upper rio Madeira basin, Mato Grosso state, Brazil. The valid name per Eschmeyer's Catalog of Fishes is Moenkhausia iris Marinho & Dagosta, 2023.
The species belongs to Moenkhausia, one of the largest and most species-rich genera in the family Characidae, with more than 80 described species distributed across tropical South America. Among its congeners, M. iris is most immediately distinguished by its unique dorso-ventral bicolour pattern, combined with a single vertically elongated humeral spot and a relatively high branched anal-fin ray count of 18–19. A congener collected from the same Chapada dos Parecis region, M. parecis, occupies the upper rio Machado drainage nearby, and the two species together reflect the plateau's role as a centre of characid diversity.
Morphology
Moenkhausia iris is a small, laterally compressed characid with the streamlined, moderate-depth body plan typical of the genus. The species is diagnosed in part by its 18–19 branched anal-fin rays and by a single humeral spot that is vertically elongated rather than the round or vague spot common in related species.
The coloration is the species' most striking feature. The dorsal half of the body is described as blue or green with an iridescent quality, while the ventral half is red, the red becoming particularly intense in the region above the anal fin. This bicolour pattern is consistent across the type series and is unlike anything recorded in other Moenkhausia species, making it both the primary diagnostic character and the basis of the species name. Detailed meristic data and maximum size are reported in the original description; size data for the wild population remain limited at the time of writing.
Habitat
The type locality is the rio Galera on the Chapada dos Parecis, a high plateau in Mato Grosso, Brazil, draining into the upper rio Guaporé and thence the rio Madeira. The Chapada dos Parecis rises above 1969 ft and feeds numerous clear, swift highland streams with sand and leaf-litter substrates — a habitat pattern shared by its congener M. parecis, which is also known from this plateau system.
Based on the habitat of that congener and the general ecology of the upper rio Madeira headwaters, the streams inhabited by M. iris are likely clear, well-oxygenated, and fast-flowing, with sandy to rocky bottoms and patches of leaf litter. The endemism of the species to a small tributary system implies a restricted range shaped by the drainage isolation of the plateau and may reflect sensitivity to habitat disturbance. Specific water-chemistry measurements from the type locality are not recorded in accessible literature.
Feeding
No feeding data specific to Moenkhausia iris have been published. Based on the diet of congeners from the same region and the general feeding ecology of small Moenkhausia species, it is probable that M. iris is an opportunistic omnivore consuming aquatic and terrestrial invertebrates, small insects, and plant material.
Its congener M. parecis, also from the Chapada dos Parecis, is documented as omnivorous, taking insects, scales from other fish, and plant matter. In an aquarium context, small Moenkhausia species generally accept a wide range of prepared and live foods; high-quality flake, micro-pellets, and frozen items such as Daphnia or artemia are suitable. A varied diet helps maintain condition and may support the vivid colours characteristic of the species.
Mating
No specific mating observations have been published for Moenkhausia iris. As a member of Moenkhausia and of Characidae more broadly, it is expected to be an open-water egg-scatterer following the typical characid reproductive mode: sexually mature individuals spawn freely without forming persistent pair bonds, and eggs are broadcast among fine-leaved vegetation or over the substrate.
Small Moenkhausia species typically display sexual dimorphism in spawning condition, with ripe females fuller-bodied than males, but no formal description of dimorphism in M. iris has been published. Given the species' novelty, hobbyist observations of mating behaviour in captivity have not yet been documented in the available literature.
Breeding
Moenkhausia iris has not yet been reported in the aquarium hobby or bred in captivity in the available literature. Based on the reproductive biology of congeners and of small characids generally, a breeding attempt would follow the egg-scattering model: conditioned adults spawning freely over fine-leaved plants or synthetic mops, depositing adhesive eggs that hatch without parental care.
Typical small characid breeding protocols — a densely planted or mop-furnished spawning tank, slight temperature increase, live or frozen conditioning foods, and removal of adults after spawning — would likely apply. Eggs and fry would require similar care to other small Moenkhausia, with infusoria or commercial liquid fry food as first foods, followed by newly hatched brine shrimp. These details remain speculative in the absence of hobbyist reports.
In the aquarium
Moenkhausia iris is, as of 2023, a newly described species not yet established in the aquarium hobby. Its striking blue-green-over-red bicolour pattern — unlike any other tetra currently in the trade — gives it obvious appeal, but availability is expected to remain very limited while the species is known only from its type locality in a small Mato Grosso stream system.
Should it become available, husbandry would likely follow the pattern of other small, active Moenkhausia tetras: a planted aquarium of moderate size with soft, slightly acidic to neutral water, kept in a school of six or more individuals, and fed a varied diet of small prepared and live foods. Its congener M. parecis thrives in clear, well-oxygenated water, suggesting that good filtration and water movement would suit M. iris. For now the species is a subject of scientific interest rather than a hobby fish, and its aquarium suitability awaits first-hand hobbyist reports.
Conservation
Moenkhausia iris has not been assessed by the IUCN Red List; as a species described in 2023, it falls outside existing formal assessments. Its known range is extremely restricted — a single small tributary system on the Chapada dos Parecis plateau — which would, under IUCN criteria, merit investigation under the Extent of Occurrence and Area of Occupancy thresholds once assessment data are gathered.
The Chapada dos Parecis is subject to expanding agricultural land use, including soy cultivation and cattle ranching, which threaten the water quality and hydrology of headwater streams. A species endemic to such a small drainage on a heavily cultivated plateau faces inherent vulnerability. Until a formal IUCN assessment is completed, the species should be regarded as potentially at risk by virtue of its narrow range alone, and collection from the type locality should be approached with caution.