Taxonomy & naming
Amazonichthys lu was described by Alexandre Lúcio Haagensen Esguícero and Fábio Baena Mendonça in 2023, in a paper published in Ichthyology & Herpetology (volume 111, issue 3, pages 426–447; DOI 10.1643/h2022010). The same paper established a second new species, Amazonichthys camelierae, and simultaneously transferred Axelrodia lindeae to the new genus as Amazonichthys lindeae — making Amazonichthys a three-species genus at its inception.
The valid name, following Eschmeyer's Catalog of Fishes (Catalog of Fishes, California Academy of Sciences), is Amazonichthys lu Esguícero & Mendonça, 2023. The genus is placed in the subfamily Aphyocharacinae within the family Characidae. FishBase lists the type locality as Brazil, South America, in freshwater.
The genus name Amazonichthys combines the Greek root for Amazon — evoking the Icamiabas, indigenous women warriors who according to accounts from the 1542 Francisco de Orellana expedition fought Spanish troops along the river that eventually bore their name — with the Greek ichthys, meaning fishes. The specific epithet lu is a proper noun in apposition, honouring Luciana Leite, known as Lu, presumably a colleague or collaborator of the authors.
Morphology
Amazonichthys lu is a very small characid with a maximum recorded standard length of 1 in (approximately 1 inch). The meristic formula recorded in FishBase gives 9 dorsal soft rays and 21 to 25 anal soft rays, with a vertebral count of 35 to 37 — a relatively high anal-ray count for a miniature characid, a trait shared with its congeners.
The species is distinguished from its two congeners, Amazonichthys camelierae and A. lindeae, by a combination of characters involving pigmentation and fin structure: poorly developed pigment on the unbranched fin rays, the absence of caudal-fin blotches that occur in the other species, and a pectoral fin composed of one unbranched ray plus eight branched rays (i8). Beyond these differential characters, the detailed osteological and meristic data appear in the original description; the published account represents the primary morphological record.
As a member of Aphyocharacinae, A. lu shares with its relatives a generally slender, compressed body form typical of small characins, with the standard characid jaw dentition and adipose fin. Its diminutive adult size places it among the smaller members of the family.
Habitat
Amazonichthys lu is native to freshwater habitats in Brazil in South America. Beyond the broad country-level distribution recorded in FishBase and the original description, detailed locality data for A. lu specifically — catchment, river system, and microhabitat — are not available in the current literature accessible through the cache, and the precise type locality has not been further qualified here.
Based on its placement in Aphyocharacinae and the environment code (benthopelagic, tropical freshwater) noted in FishBase, A. lu likely inhabits shallow, vegetated, slow-to-moderate flowing waters in lowland tropical South America, a habitat typical for small characids of this subfamily. Temperature conditions in its range are those of the lowland Amazon basin — warm tropical waters year-round. Further ecological field data await collection and publication.
Given that the species was described only in 2023 and the genus is new to science, almost nothing is documented about its ecology in natural conditions, and data on water chemistry, depth, substrate, and season preferences remain unpublished.
Feeding
No dietary studies have been published for Amazonichthys lu. Small characids of the subfamily Aphyocharacinae are generally considered micro-predators or omnivores, consuming small invertebrates — microcrustaceans, insect larvae, zooplankton — along with organic detritus and algae, opportunistically feeding in the water column and at the surface film.
In captivity, a diet of very fine live or frozen foods appropriate to the species' 1 in adult size would be essential: baby brine shrimp, micro-worms, Daphnia nauplii, and similar small invertebrates. Finely milled prepared foods may be accepted, but the species' small gape means particle size is a limiting factor. Detailed captive-feeding observations are absent from the available literature, and the above is extrapolated from the biology of comparable miniature characids.
Mating
No observations of mating behaviour in Amazonichthys lu have been published. Small characids of the family Characidae are broadly egg-scatterers that spawn in open water or among fine-leaved aquatic plants, with males pursuing and courting females and no subsequent parental involvement.
By analogy with other small Aphyocharacinae, A. lu is likely a non-guarding, open or plant-associated egg-scatterer in which females deposit adhesive or semi-adhesive eggs among fine-leaved vegetation or submerged roots. Males probably court females through rapid pursuit and parallel swimming, with no lasting pair bond. Sexual dimorphism, if present, has not been formally characterised in the original description based on available notes.
Breeding
Breeding in captivity has not been documented in the available literature for Amazonichthys lu. Given the species' membership in Characidae and its very small adult size, captive breeding, if achieved, would likely follow the general pattern of miniature characid aquarium species: egg-scattering spawning over fine-leaved plants or spawning mops, with adhesive eggs that hatch within a few days at tropical temperatures, and very small fry requiring infusoria or rotifers as first foods.
Parental care is not expected based on family-level biology — adults should be removed after spawning to prevent egg predation. The difficulty in obtaining and maintaining wild-caught specimens of such a newly described and obscure species means that captive breeding remains essentially uncharted territory. No clutch sizes, incubation periods, or rearing protocols specific to A. lu are available.
In the aquarium
Amazonichthys lu is essentially unknown in the aquarium hobby as of the time of writing. Described only in 2023, it has not appeared in trade listings or hobbyist literature accessible through the current research cache, and it is unlikely to be commercially available outside of specialist ichthyological collections or very rare wild imports from Brazil.
For any aquarist who does obtain the species, the guiding principle is its adult size: at 1 in SL, Amazonichthys lu is a true nano fish that requires tankmates scaled accordingly. A species-only setup or a nano community with other micro-tetras, small rasboras, or dwarf invertebrates would be appropriate. A heavily planted aquarium with gentle filtration, soft to moderately soft tropical freshwater, and dim lighting replicating dappled forest-stream conditions would be a reasonable starting point based on the biology of its subfamily, pending published husbandry data. The species' rarity means hobbyist experience is effectively zero, and extrapolations from related genera carry significant uncertainty.
Conservation
Amazonichthys lu has not been assessed by the IUCN Red List and carries a status of Not Evaluated (NE). As a species described only in 2023, it predates any formal conservation evaluation, and no population estimates, threat assessments, or range maps are available in the published literature.
The species is native to Brazil, which encompasses a substantial portion of the Amazon basin, a region subject to ongoing deforestation, agricultural expansion, mining, and hydrological alteration. Whether A. lu is broadly distributed across low-risk habitat or restricted to a narrow endemic range is not known from current data. Until field surveys establish its distribution and abundance, and until an IUCN assessment can be completed, the conservation status of this species cannot be meaningfully characterised. Its very recent description underscores that Amazonian freshwater biodiversity remains incompletely documented, and small characids continue to yield new species to systematic surveys.