Taxonomy & naming
Deuterodon oyakawai was described by Santos and Castro in 2014, with the original combination Probolodus oyakawai. The species was subsequently transferred to Deuterodon by Terán et al. (2020) following phylogenetic work that revised the boundaries of these two closely related Neotropical characid genera. Eschmeyer's Catalog of Fishes, the authority for valid names, records the current valid combination as Deuterodon oyakawai (Santos & Castro, 2014); the parenthetical authority reflects the fact that the species was not originally placed in Deuterodon.
Deuterodon oyakawai is distinguished from its congeners by a combination of skeletal and squamation characters. The Plazi TreatmentBank treatment citing the original description notes diagnostic features including the epural bone not leaning against the urostyle and the first and second infraorbitals contacting but not overlapping — characters that separate it within the genus. Meristic data from FishBase record 11 dorsal soft rays, 33–34 vertebrae, 41–43 perforated lateral-line scales, and 14–16 scales around the caudal peduncle.
Morphology
Deuterodon oyakawai is a small, slender characid reaching a maximum recorded standard length of 2.5 in. Like other members of the genus it has the typical body plan of a small Neotropical stream tetra: a moderately compressed, fusiform body, a complete lateral line, and the adipose fin characteristic of the family. The species' diagnostic meristic combination — 41–43 perforated lateral-line scales and 14–16 circumferential scales around the caudal peduncle — distinguishes it from sympatric congeners in the rio Ribeira de Iguape drainage.
Detailed colour pattern information is sparse in available sources. As with many small characids of the genus, the fish is likely silvery with the subtle lateral banding typical of the group, though striking secondary coloration has not been reported for this species. The relatively modest trophic level of 3.1 recorded in FishBase is consistent with a mixed diet, including the occasional scale-scraping events that characterise the group's feeding ecology.
Habitat
The species is endemic to the rio Ribeira de Iguape basin in the Atlantic Forest biome of southeastern Brazil, where it is known from freshwater, benthopelagic environments classified as tropical. The Ribeira de Iguape is one of the few large river systems in southeastern Brazil that retains substantial forest cover in its headwaters, supporting a diverse and partially endemic ichthyofauna.
Specific microhabitat data for Deuterodon oyakawai are sparse in available records, but members of the genus typically occupy clear to moderately turbid streams and small rivers with substrates of sand, gravel, or leaf litter, often associated with riparian vegetation and submerged roots. The original collection of the type series was made in large part by Osvaldo T. Oyakawa of the Museu de Zoologia da Universidade de São Paulo, who has documented the ichthyofauna of the Ribeira basin extensively and whose material informed both the species description and broader surveys of the basin's fish diversity.
Feeding
FishBase records scales in the stomach contents of Deuterodon oyakawai, confirming lepidophagy — the habit of scraping or biting scales from other fishes — as part of this species' dietary repertoire. Lepidophagy is rare among tetras and is perhaps best known from Probolodus heterostomus, the genus from which oyakawai was originally described; the shared feeding strategy may reflect a phylogenetic signal now formally resolved by its placement in Deuterodon.
Scale-scraping in characids is generally facultative rather than obligate: fish engaging in lepidophagy also consume invertebrates, algae, and detritus as opportunity allows, and the low trophic level of 3.1 recorded for the species is consistent with a broadly opportunistic rather than exclusively predatory diet. In the aquarium, specific dietary observations are not documented in available literature, but small Deuterodon are typically kept on good-quality flake and micro-pellet foods supplemented with live or frozen invertebrates.
Mating
No specific mating data have been published for Deuterodon oyakawai. Reproductive biology information for the species is absent from available sources, and the species has not been documented in the aquarium hobby literature where such observations would typically accumulate.
By analogy with other small Neotropical stream characids of the genus and family, the species is expected to be an egg-scattering open spawner without parental care, releasing adhesive or semi-adhesive eggs among fine-leaved vegetation, submerged roots, or over leaf-litter substrate. Spawning in many Neotropical tetras is linked to seasonal water-temperature and photoperiod cues, often peaking at the onset of the wet season when conditions for larval survival improve. These inferences remain unconfirmed for this species.
Breeding
No captive breeding records for Deuterodon oyakawai appear in available sources. The species is not established in the ornamental fish trade and is unlikely to be kept by hobbyists at present; the sparse husbandry record reflects its status as a recently described, range-restricted endemic known primarily from scientific collections.
For hobbyists who might obtain specimens, the general approach for small Neotropical stream tetras would apply: a well-planted breeding aquarium with soft, slightly acidic water, a temperature in the mid-20s Celsius, and fine-leaved plants or spawning mops as egg substrate. Given the lepidophagous tendencies documented for the species, tankmates in a breeding setup — and the breeding pair themselves — should be chosen with care, as scale-biting can cause injury to companions and stress to the target fish.
In the aquarium
Deuterodon oyakawai is not an established aquarium fish. It does not appear in the ornamental trade literature, and available records come entirely from scientific survey collections in the rio Ribeira de Iguape basin. Hobbyists seeking fish from this drainage would more readily encounter other Brazilian tetras for which trade supply chains and captive husbandry are documented.
The species' lepidophagous diet merits attention for anyone who does acquire specimens: fish that scrape scales can injure tankmates, particularly slow-moving or long-finned species. Any aquarium housing this species would do well to provide plenty of cover, a varied diet to reduce scale-biting pressure, and compatible tankmates of comparable size and speed. Water parameters consistent with the warm, tropical freshwater habitats of the Ribeira basin — a temperature of roughly 72–79 °F, neutral to slightly acidic pH, and soft to moderately hard water — would be the baseline starting point.
Conservation
Deuterodon oyakawai has not been formally assessed by the IUCN Red List; its conservation status is Not Evaluated (NE). As an endemic restricted to the rio Ribeira de Iguape basin, it is subject to pressures that affect much of the Atlantic Forest fish fauna: habitat loss through deforestation, agricultural runoff, and water abstraction, as well as ongoing modification of river hydrology in the basin.
The Ribeira de Iguape watershed is recognised as one of the most biodiverse river systems remaining in the Atlantic Forest biome, with a high proportion of endemic species and relatively intact headwater habitats compared to other southeastern Brazilian drainages. Conservation of the broader basin ecosystem is therefore directly relevant to the persistence of narrow endemics such as this species. Formal assessment through the Brazilian national red-list process or the IUCN would help clarify the species' vulnerability and guide any targeted protection measures.