Taxonomy & naming
Myxiops aphos was described by Angela M. Zanata and Alexandre Akama in 2004, making it the founding and only species of the genus Myxiops at the time of its description. The valid name, as recorded in Eschmeyer's Catalog of Fishes, is Myxiops aphos Zanata & Akama, 2004; authority is not parenthetical because the species was described in Myxiops, the genus in which it still resides. The type locality is the Rio Lençóis system in Bahia, Brazil.
Myxiops belongs to the family Characidae, the largest family of freshwater fishes in the Neotropical region. Within Characidae the genus has been placed among the smaller, more derived lineages of the family, characterized by features of the mouth and oral anatomy that distinguish it from superficially similar small characids occurring elsewhere in the São Francisco basin drainage network. The specific epithet aphos is derived from the Greek word for 'simple' or 'without adornment,' an apt choice for a small, plainly coloured fish whose distinguishing features lie more in morphological detail than in vivid pattern.
Morphology
Myxiops aphos is a small, slender characid reaching a maximum recorded standard length of 2 in. The body form is elongate and moderately compressed laterally, typical of a fish adapted to life in flowing water. Like most small characids it possesses the family's characteristic adipose fin — a small fleshy fin on the dorsal ridge between the dorsal and caudal fins that is not supported by rays.
Coloration is understated: the body is generally silvery, often with a pale golden or straw-yellow wash, and a darker mid-lateral stripe or diffuse band may be evident depending on preservation state and light conditions. The fins are largely hyaline. No bold colour markings appear to be associated with the species in available descriptions, consistent with the specific epithet's allusion to simplicity. Sexual dimorphism, if present, has not been prominently described in the literature accessible for this species.
Habitat
Myxiops aphos is known from the Rio Lençóis in Bahia, a river system draining part of the Chapada Diamantina highlands of interior northeastern Brazil. Streams of this region are typically clear, well-oxygenated, and fast-flowing in their upper reaches, running over rocky or sandy substrates through a landscape of cerrado savanna and caatinga scrubland. The drainage falls within the broader São Francisco River basin, one of the great river systems of eastern Brazil.
As a benthopelagic freshwater fish recorded from tropical Brazil, Myxiops aphos likely inhabits shallow riffles and runs where current provides oxygenation, as is characteristic of many small characids of the Chapada Diamantina region. The Rio Lençóis system is notable for its relatively clear water and is subject to seasonal fluctuation in flow, which is typical of rivers draining the semi-arid interior of Bahia.
Feeding
No detailed dietary study of Myxiops aphos appears in the available literature. As a small characid from flowing, well-oxygenated streams, it can reasonably be inferred to be an opportunistic omnivore, taking small invertebrates — aquatic insect larvae, microcrustaceans, and similar invertebrate prey — along with algae and organic detritus encountered in the current. This feeding guild is common among small-bodied Characidae of similar size and habitat in northeastern Brazil.
In captivity, small characids of comparable size and morphology are typically maintained on a varied diet of fine dried foods supplemented with small live or frozen invertebrates such as Daphnia, Artemia nauplii, and micro-worms. The species is unlikely to prove a specialist feeder, but specific dietary observations in captivity are not documented in sources available for this account.
Mating
No detailed observations on the mating behaviour of Myxiops aphos are available in the literature consulted for this account. Based on its placement in Characidae and its small body size, the species is expected to follow the widespread characid pattern of egg-scattering open spawning, in which males court females with no formation of lasting pair bonds and both sexes scatter adhesive or semi-adhesive eggs among fine-leaved vegetation, submerged roots, or over the substrate, with no subsequent parental care.
Male–female differences in behaviour at spawning time — such as the abdominal distension of ripe females common across small characids — would be expected but have not been specifically documented for this species in the sources available.
Breeding
Breeding in captivity has not been documented in the sources available for this account. By analogy with other small, stream-dwelling South American characids, Myxiops aphos would be expected to spawn over fine-leaved plants or spawning mops, depositing small, adhesive eggs that the adults will consume if not removed. Rearing would follow the standard small-tetra protocol: isolation of eggs or spawning medium, hatching after several days at tropical temperatures, and feeding of the small fry on infusoria or commercial fry foods before graduating to newly hatched brine shrimp.
Until captive breeding records exist for this species, all breeding guidance should be treated as inference from closely related taxa rather than confirmed observation.
In the aquarium
Myxiops aphos is not an established aquarium species and is not known to be available in the ornamental trade at the time of writing. Its small size — under 2.5 in standard length — and its origins in clear, well-oxygenated Bahian highland streams suggest it would require clean, well-filtered water with moderate to good current, cooler temperatures appropriate to upland Brazilian streams, and a diet of small live and frozen invertebrates supplemented with fine prepared foods.
Should it ever become available to specialist keepers, it would best suit a species aquarium or a tank with similarly small, peaceful fishes from the same biogeographic region. Its scientific rather than ornamental appeal places it primarily in the realm of ichthyologists and collectors of unusual South American characids rather than the general aquarium hobby.
Conservation
Myxiops aphos is assessed as Least Concern (LC) on the IUCN Red List, with an assessment dated 7 November 2018. Although its known range is restricted to the Rio Lençóis system in Bahia, the species is apparently not under immediate threat at the population level sufficient to qualify for a threatened category under current criteria.
The Rio Lençóis drainage and the broader Chapada Diamantina region of Bahia are not without environmental pressure — the semi-arid northeastern interior of Brazil faces challenges from agricultural water use, river regulation, and land-cover change — and the restricted range of a single-river endemic warrants ongoing monitoring. The Least Concern assessment reflects the state of knowledge as of 2018; any significant degradation of the Lençóis headwaters could alter the picture for a species with nowhere else to occur.