Taxonomy & naming
Moenkhausia takasei was described by Jacques Géry in 1964 in the hobbyist journal Tropical Fish Hobbyist, under the title 'Two new tetras from the Lower Amazon Basin'. The type locality is a creek near Belém do Pará in the Rio Guamá basin, lower Amazon, Brazil; the holotype is deposited at the Smithsonian Institution as USNM 198136. Eschmeyer's Catalog of Fishes records the valid name as Moenkhausia takasei Géry, 1964; no subsequent revision has moved it from Moenkhausia, so no parenthetical authority is used.
Moenkhausia is one of the largest characid genera, comprising more than eighty recognised species distributed across tropical South America. It is a notoriously difficult assemblage to characterise on shared derived characters, and several molecular studies have flagged it as likely polyphyletic; taxonomic reshuffling within the group is ongoing. M. takasei is a small, relatively slender member of the genus whose precise affinities within Moenkhausia have not been investigated in depth in the published literature.
Morphology
Moenkhausia takasei is a small fish, with FishBase recording a maximum standard length of 1.5 in. Like most members of its genus it is a laterally compressed, fusiform characid with a forked tail, a single dorsal fin, and the adipose fin characteristic of the family. Detailed meristic data for the species are sparse in the broadly accessible literature.
The species lacks a widely recognised common name, suggesting it has not achieved mainstream hobby status. Its small size places it firmly in the category of nano or dwarf tetras, comparable in scale to members of the Hyphessobrycon and Hemigrammus assemblages rather than to the larger species of Moenkhausia such as M. oligolepis.
Habitat
The known type locality of Moenkhausia takasei is a creek near Belém do Pará in the Rio Guamá drainage, which is part of the lower Amazon basin in the state of Pará, Brazil. FishBase characterises the species as a benthopelagic tropical freshwater fish, suggesting it occupies the water column near the bottom as well as open water in small, sheltered water bodies.
The lower Amazon and its associated creeks and igapó systems in the Pará region are typically soft and acidic, with low conductivity, warm temperatures, and heavy tannin staining from decomposing leaf litter. Creek habitats in this region often have dense marginal and overhanging vegetation. Beyond the type locality, the full distributional extent of M. takasei within the lower Amazon basin is not well documented.
Feeding
No species-specific dietary data have been published for Moenkhausia takasei. Based on the feeding ecology of similarly sized characids from comparable Amazonian creek habitats, the species is likely an opportunistic omnivore taking small invertebrates, zooplankton, and organic particles in the water column and at the surface.
In the aquarium, small tetras of this size category are typically maintained on a varied diet of high-quality micro-pellets or fine flake, supplemented with small live or frozen foods such as Daphnia, micro-worm, and baby brine shrimp. Such a diet supports natural condition and colouration.
Mating
No species-specific mating or courtship observations have been published for Moenkhausia takasei. As a member of Moenkhausia — a genus of open egg-scatterers — it is expected to follow the typical characid pattern in which males court females with brief chasing displays before spawning over fine-leaved vegetation or substrate, with no lasting pair bond.
Related Moenkhausia species and other small Amazonian tetras commonly spawn in soft, slightly acidic water among dense plants. Spawning activity in small characids is typically most intense in the early morning hours, and males in a group setting may display against one another to establish hierarchical status before courting females.
Breeding
No detailed breeding account for Moenkhausia takasei specifically has been located in the available literature. Based on the reproductive biology of the genus, M. takasei is presumed to be an egg-scattering, open spawner that deposits small, adhesive or semi-adhesive eggs among fine-leaved plants, with no parental care; adults will eat eggs and must be separated from them after spawning.
For related Moenkhausia species, soft and slightly acidic water (pH around 5.5–6.5, low general hardness) is typically recommended for breeding, with temperatures in the 79–82 °F range. Eggs generally hatch within 24–36 hours under these conditions. Fry require infusoria or commercial liquid fry food initially, graduating to newly hatched brine shrimp as they grow. Given the species' very small size, fry are likely correspondingly tiny and may need especially fine first foods.
In the aquarium
Moenkhausia takasei is noted by FishBase as being kept in the commercial aquarium trade, though it does not appear in the mainstream hobby literature with any frequency, and no dedicated care guide has been widely circulated. Its very small adult size of 1.5 in SL makes it well suited to smaller aquaria and nano setups, where it could be housed in a planted tank with subdued lighting, a dark substrate, and gentle filtration.
As a lower Amazon creek species it is likely to do best in soft, slightly acidic to neutral water kept warm (around 75–82 °F), conditions that mimic the tannin-stained creek systems of the Pará region. A shoal of six or more individuals is preferable, as small tetras show more natural behaviour in groups. Tankmates should be small and peaceful — other micro-tetras, small corydoras, or dwarf cichlids would be appropriate choices. Little else is documented, and hobbyists keeping this species are encouraged to record and share observations.
Conservation
Moenkhausia takasei is assessed as Data Deficient (DD) on the IUCN Red List, with the assessment dated 4 March 2021. A Data Deficient listing indicates that there is insufficient information to make a direct or indirect assessment of the species' risk of extinction, not that it is necessarily threatened or secure.
FishBase notes a high resilience for the species, with an estimated population doubling time of fewer than 15 months, which if accurate would suggest reasonable demographic robustness. However, the paucity of distributional and population data means that threats from habitat degradation in the lower Amazon — including deforestation, agricultural runoff, and urban expansion around Belém — cannot be assessed against known population status. Continued systematic surveying of small-bodied characids in the lower Amazon creek systems would be needed to move this species out of the Data Deficient category.