Taxonomy & naming
Hyphessobrycon comodoro was described by Dagosta, Seren, Ferreira & Marinho in 2022, with the original description published in Neotropical Ichthyology. The type locality is a lagoon tributary of the rio Mutum in the Municipality of Comodoro, Mato Grosso State, Brazil, placing the species within the upper rio Juruena basin, which drains into the rio Tapajós system and ultimately the Amazon. Eschmeyer's Catalog of Fishes is the governing authority for the valid name; because the species was described directly into Hyphessobrycon and the name has not been revised, no parenthetical authority is used.
Hyphessobrycon is one of the largest and most heterogeneous characid genera, comprising well over 150 described species distributed widely across South America. The genus is defined largely by a combination of small size, presence of an adipose fin, and features of dentition and the lateral line, though molecular and morphological revisions have repeatedly shown it to be polyphyletic. H. comodoro is currently placed in Hyphessobrycon pending any broader generic revision that might affect that placement. Its closest relatives within the genus have not been formally published as of the time of description.
Morphology
Hyphessobrycon comodoro is a small, slender tetra. FishBase records a maximum size of 1.5 in standard length for males and unsexed specimens, firmly placing it in the nano category alongside other diminutive Hyphessobrycon. The body is laterally compressed and streamlined, typical of active open-water tetras. An adipose fin is present, as in virtually all characids of this group.
The common name 'Emerald Green Tetra' reflects the species' most conspicuous feature: an iridescent green sheen across much of the body, strongest along the flanks under good lighting. The precise extent and intensity of the colour, including any red or orange accents on the fins or body, have not been fully documented in published aquarium literature given the species' recent description. As with most Hyphessobrycon, males are likely slimmer and may show more vivid colouration, while females are deeper-bodied when in spawning condition, but detailed dimorphism data are sparse for this species.
Habitat
The type locality is a lagoon tributary of the rio Mutum in the upper rio Juruena basin, Mato Grosso State, Brazil. This tributary, described in the original paper, had transparent water, a width of 164–197 ft, and a depth of 1–7 ft. The substrate was sand and silt with organic matter, and aquatic macrophytes and filamentous algae were present. FishBase categorises the species as benthopelagic, occurring at 0–7 ft depth in clear, rapid tropical waters.
The upper rio Juruena is a highland tributary of the Tapajós, draining parts of the cerrado-Amazon transition zone of Mato Grosso. Clear, transparent waters in this region are typically slightly acidic to neutral, relatively low in dissolved minerals, and warm year-round. The presence of macrophytes and organic matter at the type locality suggests the fish inhabits slow marginal or lagoon habitats adjacent to the main channel rather than fast-flowing open water.
Feeding
Stomach-content data from the original description indicate that H. comodoro is predominantly an autochthonous feeder: 91.6% of dietary items were of internal aquatic origin, comprising 57.7% plant fragments and 32.7% aquatic insects. This makes it somewhat more herbivorous or detritivorous than many tetras of similar size, though aquatic insects form a meaningful component. Allochthonous material (terrestrial matter) was a minor fraction.
In the aquarium, the feeding requirements of this species are consistent with other small Hyphessobrycon: good-quality micro-pellets or crushed flake, supplemented with small live or frozen invertebrates such as Daphnia, baby brine shrimp, and micro-worms. Offering some plant-based or algae-containing foods may better reflect the natural diet. Like all small tetras it benefits from frequent small feedings rather than one large daily meal.
Mating
No published mating observations specific to H. comodoro are available. Based on its placement in Hyphessobrycon and the general biology of the genus, it is expected to be an egg-scattering open spawner with no parental care. Males of small Hyphessobrycon typically court females with lateral displays and fin-flaring, with spawning activity peaking in the morning. Adhesive or semi-adhesive eggs are scattered among fine-leaved aquatic plants or over a substrate of organic matter.
In an aquarium setting, conditioning with varied live and frozen foods encourages males to display and females to develop eggs. Spawning activity is generally triggered by slightly warmer water or a water change simulating a rain event, as is common in tetras from seasonally variable Amazonian drainages.
Breeding
Specific captive-breeding records for H. comodoro have not been published in the hobbyist literature at the time of this writing, reflecting its status as a recently described, rarely traded species. General Hyphessobrycon breeding protocols apply: a species tank or breeding tank with fine-leaved plants such as Java moss or a synthetic spawning mop, subdued lighting, and soft, slightly acidic water at around 79–82 °F is the standard starting point. Adults are egg-scatterers and will consume their own spawn, so breeders should either remove adults after spawning or densely plant the tank to provide egg cover.
Eggs of small Hyphessobrycon typically hatch within 24–36 hours at breeding temperatures, with fry becoming free-swimming after a further 3–4 days. First foods are infusoria and rotifers, progressing to freshly hatched brine shrimp nauplii once fry are large enough. The emerald colouration is likely to develop gradually as juveniles mature, as is common in iridescent tetras.
In the aquarium
H. comodoro remains rare in the hobby as of its 2022 description, and specimens that do appear in trade are likely wild-caught or from small specialist breeders. Its small adult size (under 1.5 in SL) and reported emerald green colouration make it an attractive candidate for well-planted nano or small community aquaria. A group of at least six individuals is advisable to allow natural shoaling behaviour and reduce individual stress.
Water chemistry should reflect the transparent, slightly acidic conditions of its native upper Juruena habitat: soft to moderately soft water, pH in the range 6.0–7.5, and temperatures of 75–82 °F. Hobbyist sources note that water chemistry need not be critical, with a tolerance up to pH 8.0 reported, but quality — low nitrates, stable parameters, and the tannin and humic character of a mature planted tank or a tank with driftwood — likely produces the best colour and health. Tankmates should be small, peaceful species of similar size; fin-nippers should be avoided. Because the species is so recently described, aquarists keeping it are encouraged to document behaviour and share observations with the broader hobby community.
Conservation
Hyphessobrycon comodoro has not been assessed by the IUCN Red List and carries a status of Not Evaluated (NE). Its known range appears restricted to the upper rio Juruena drainage in Mato Grosso State, Brazil, based on the type locality and associated collections. Endemism to a single drainage in a region subject to ongoing agricultural expansion — the Mato Grosso cerrado and Amazon transition zone is one of Brazil's most rapidly deforested areas — represents a potential conservation concern, though no formal population assessment has been conducted.
The species' small size and habitat in lagoon and marginal tributary environments may make it vulnerable to sedimentation and water-quality changes associated with land clearance and cattle ranching in the Juruena basin. Until a formal IUCN assessment is undertaken, its conservation status will remain unquantified. Aquarists who succeed in breeding it are contributing, however modestly, to maintaining a captive population of a range-restricted and still obscure species.