Taxonomy & naming
Astyanax keronolepis was described in 2019 by Silva, Malabarba & Malabarba, and is recorded as a valid species in Eschmeyer's Catalog of Fishes (Characidae, Characiformes). The type locality and distribution are restricted to coastal drainages of southeastern Brazil, encompassing a narrow corridor from Ubatuba, São Paulo, to the Guapimirim River basin in Rio de Janeiro state.
The species belongs to Astyanax Baird & Girard, 1854 — one of the largest and most taxonomically complex genera in Neotropical freshwater ichthyology, with well over 100 valid species distributed from northern Mexico through South America. Many members of the genus are morphologically conservative, and new species continue to be described as regional surveys fill in the Atlantic Forest coastal zone. The placement of A. keronolepis in Astyanax follows current usage in the Catalog of Fishes, which is the governing authority for the valid name.
Morphology
Astyanax keronolepis reaches a maximum recorded standard length of 4 in, making it a mid-sized member of the genus. Like most Astyanax it has the typical characid body plan: moderately compressed laterally, a forked tail, a small adipose fin behind the dorsal, and the paired rows of teeth characteristic of the family.
Specific diagnostic characters distinguishing A. keronolepis from congeners were established in the original description and are tied to the morphological details documented for the type series. As a species described primarily from museum material, detailed external colour notes in life are not widely reported in secondary literature; the species is not established in the ornamental trade and hobbyist colour accounts are essentially absent.
Habitat
Astyanax keronolepis is a freshwater specialist endemic to a short stretch of the Atlantic Forest coastal plain in southeastern Brazil. Its known range runs from the vicinity of Ubatuba in São Paulo state to the Guapimirim River basin in Rio de Janeiro — a coastal corridor that drains directly to the Atlantic rather than into the major interior basins.
Within this zone the species inhabits rapid, crystalline streams with rocky substrates covered in algae. This habitat profile — fast current, high transparency, and algae-encrusted rock — is characteristic of well-oxygenated upper drainages in the Serra do Mar escarpment system. The Atlantic Forest coast of southeastern Brazil is one of the most threatened ecoregions on Earth: extensive deforestation, urbanisation, and agricultural conversion have severely fragmented remaining natural stream habitat, and many freshwater endemics of the region face pressure from these landscape-level changes.
Feeding
FishBase records Astyanax keronolepis as feeding predominantly on vegetable matter — algae and plant material — with hymenoptera (ants and their relatives) making up an occasional component of the diet. This emphasis on plant-based food is somewhat unusual among Astyanax, many of which are broadly omnivorous with a stronger invertebrate component, and likely reflects the algae-rich rocky substrate the species inhabits in the wild.
In an aquarium context, a diet weighted toward vegetable-based foods — spirulina flake, blanched vegetable matter, algae wafers — alongside standard omnivore flake and the occasional small live or frozen invertebrate food would approximate natural feeding. As with other characids, varied feeding improves condition.
Mating
No species-specific mating observations have been published for Astyanax keronolepis. Based on genus-level reproductive biology documented for Astyanax more broadly, the species is expected to follow the typical characid pattern: egg-scattering open spawning with no pair bond formation and no parental care.
Males in reproductive condition likely display to females using characteristic characid posturing and fin-spreading. Spawning in Astyanax species generally occurs in association with fine-leaved aquatic vegetation or other structure over which adhesive or semi-adhesive eggs are scattered. Reproductive activity in some Astyanax species is described as opportunistic and extended seasonally rather than tightly pulse-triggered, with multiple spawning events possible within a breeding season.
Breeding
Astyanax keronolepis has not been documented in captive breeding accounts, and it is not available in the ornamental trade. Extrapolating from genus-level reproductive data, breeding in Astyanax typically involves batch spawning of small oocytes deposited among fine-leaved plants or over open substrate, with no subsequent parental care. Adults will consume eggs if given the opportunity.
In laboratory settings, Astyanax species have been brought into reproductive condition with temperature increases into the range of 72–77 °F and conditioning on varied foods. Fry are small at hatching and require fine first foods. Given the species' restricted and threatened range, it has not come to the attention of specialist breeders, and no published captive-breeding protocol exists.
In the aquarium
Astyanax keronolepis is essentially unknown in the ornamental trade and is not available through standard hobby channels. Its description from a narrow endemic range in coastal Brazil makes wild collection for export unlikely to have occurred at any meaningful scale, and it has not been established as a captive-bred species.
Should specimens become available, the habitat profile suggests they would do best in well-oxygenated, clean water with moderate to strong current, a temperature range consistent with subtropical coastal Brazil (roughly 64–75 °F), and rock or gravel substrate with algal growth. As a mid-sized Astyanax, it would likely prove a robust, schooling fish compatible with similarly sized peaceful tankmates. The species' diet leanings toward vegetable matter suggest supplementing with algae-based foods. In practice, aquarists interested in Atlantic Forest endemics are better served by the handful of A. bimaculatus or related Astyanax that do appear in trade.
Conservation
Astyanax keronolepis has not been formally assessed by the IUCN Red List and carries a status of Not Evaluated (NE). The species was only described in 2019, and newly described taxa frequently lag behind the assessment process. However, the biological facts point to genuine conservation concern: it is a freshwater endemic with a range confined to a narrow coastal strip in southeastern Brazil, and that coastal Atlantic Forest zone is one of the most heavily degraded freshwater regions in South America.
Stream habitats in the Ubatuba–Guapimirim corridor face pressure from urban expansion in one of the most densely populated regions of Brazil, agricultural runoff, and the loss of riparian vegetation that maintains water quality and the cool, oxygenated conditions fast-water specialists require. A formal IUCN assessment, using criteria accounting for the species' restricted range and the condition of its habitat, would be a valuable step in understanding its conservation needs.