Taxonomy & naming
Astyanax cubilhuitz was described by Juan Julio Schmitter-Soto in 2017, as one of nine new species introduced in a major systematic revision of Central and North American Astyanax published in the Journal of Natural History (vol. 51, no. 21–24, pp. 1331–1424). The holotype, UMMZ 250290, is a specimen of 2 in standard length collected from the spring that gives rise to a short stream with underground drainage to the Río Dolores, at the locality of Cubilhuitz, Alta Verapaz, Guatemala, at an elevation of approximately 984 ft. The species epithet is a noun in apposition taken directly from the type locality name, Cubilhuitz.
Astyanax is by far the most species-rich characid genus in the Americas, and its taxonomy has long been complicated by widespread morphological conservatism across the group. Schmitter-Soto's 2017 revision applied meristic and morphometric analyses to untangle Central American diversity, distinguishing cubilhuitz from its congeners on the basis of body proportions and fin-ray counts, including a body depth of 35% of standard length or less, an eye diameter of approximately 35% of head length, and an anal-fin ray count of 21–26. The Catalog of Fishes (Eschmeyer, CAS) records the valid name as Astyanax cubilhuitz Schmitter-Soto, 2017.
Morphology
Astyanax cubilhuitz is a small, slender tetra with the holotype measuring 2 in standard length, and FishBase reports a maximum size of 2 in SL — a figure derived from the type series. Like other members of the genus it has the characteristic Astyanax body plan: a moderately compressed, fusiform profile, a relatively large eye, a short snout, and the small adipose fin positioned between the dorsal and caudal fins that is typical of characids.
Diagnostic meristic characters noted in the original description include nine dorsal-fin rays, an anal-fin ray count in the range of 21–26, and a single row of short scales along the anal-fin base. Eye diameter is relatively large at roughly 35% of head length, and body depth does not exceed 35% of standard length, giving the species a somewhat slender profile compared with some congeners. No nuptial tubercles were recorded in the type series.
Habitat
The species is known exclusively from the type locality: the spring head of a short surface stream at Cubilhuitz, Alta Verapaz, Guatemala, which drains underground into the Río Dolores. This is a karstic landscape at approximately 984 ft elevation, characterised by limestone geology with subterranean stream segments that resurface as springs. The Río Dolores drains into Atlantic-slope river systems in the broader Guatemala highlands.
The spring-origin habitat suggests cool, well-oxygenated, hard water buffered by carbonate bedrock — conditions typical of karst springs in highland Central America. No detailed water-chemistry data for the specific site were provided in the available sources. The subterranean drainage component of the system means surface habitat is limited and potentially isolated, a feature common to many narrow-range karstic endemics in the region.
Feeding
No published feeding observations exist for Astyanax cubilhuitz specifically. Members of the genus are broadly omnivorous opportunists, taking small invertebrates, algae, plant material, and particulate organic matter as available in their respective habitats. Spring-fed karstic streams typically support invertebrate communities including insect larvae, small crustaceans, and worms, which would be expected prey items for a small characid of this size.
In an aquarium setting, congeners of similar size accept quality flake foods, micro-pellets, and a variety of small live and frozen foods including Daphnia, Artemia nauplii, and chironomid larvae. There is no information specific to this species in captivity.
Mating
No specific mating observations have been published for Astyanax cubilhuitz. The genus is broadly characterised as egg-scattering, open-water or plant-associated spawners without parental care — the typical reproductive strategy across the Characidae. In species where it has been studied, male Astyanax pursue females in short bursts, and the pair release eggs and milt simultaneously in open water or among fine-leaved vegetation, with the adhesive or semi-adhesive eggs settling among plants or substrate.
No nuptial tubercles were noted in the original type series of A. cubilhuitz, and the original description does not comment on sexual dimorphism or breeding behaviour. Given the small body size, spawning activity would be expected to follow broadly typical characid patterns, but details remain unrecorded.
Breeding
Astyanax cubilhuitz has not been reported in captive breeding. Based on the biology of congeners, the expected pattern is open egg-scattering over fine-leaved plants or substrate with no parental investment; adults would be expected to consume their own eggs if left in the same container. Eggs of similarly sized Astyanax species are typically small, adhesive to semi-adhesive, and hatch within two to four days at tropical temperatures, with larvae becoming free-swimming shortly thereafter.
No captive husbandry or breeding records were located for this species. Given its restricted wild range and apparent rarity in the hobby, captive breeding information is data sparse.
In the aquarium
Astyanax cubilhuitz is not an established aquarium fish. No trade records or hobbyist accounts were found, and the species appears to be essentially unknown in captivity. Its small size — maximally around 2 in SL — and presumed peaceful, schooling temperament suggest it would be manageable in a modest aquarium if it were ever collected and maintained, but any such details remain speculative.
Given the karstic spring origin of the type locality, water with moderate to high hardness and a neutral to slightly alkaline pH would likely suit the species better than the soft, acidic conditions often favoured for Amazonian tetras. No care-rating can responsibly be assigned from the available information.
Conservation
Astyanax cubilhuitz has not been formally assessed by the IUCN Red List and carries a status of Not Evaluated as of 2025. The species is a narrow-range endemic known only from a single spring system in Alta Verapaz, Guatemala — a restricted type locality that makes it intrinsically vulnerable to any disturbance affecting that watercourse. The subterranean karst drainage system the stream feeds into adds further complexity: pollutants or hydrological changes entering the underground aquifer could affect the spring output without any surface-visible warning.
Guatemala's highland karst systems face pressure from agricultural runoff, deforestation of riparian zones, and water extraction. Without a formal range survey it is not possible to say whether the species occurs elsewhere in the Río Dolores catchment or is truly confined to the Cubilhuitz spring. A targeted field survey and formal IUCN assessment would be the appropriate first steps toward understanding its conservation needs.