Taxonomy & naming
Astyanax guaricana was formally described by Claudio Oliveira, Vinícius Abilhoa, and Carla S. Pavanelli in 2013, in the journal Neotropical Ichthyology (volume 11, pp. 291–296). The holotype, MZUSP 112224, was collected from the rio Arraial, an affluent of the rio Cubatão feeding the Guaricana Reservoir in the municipality of São José dos Pinhais, Paraná State, southern Brazil (25°42'29"S 48°58'25"W). The Catalog of Fishes (Eschmeyer) records the valid name as Astyanax guaricana Oliveira, Abilhoa & Pavanelli, 2013.
The species is placed within the Astyanax scabripinnis species complex, a large and unresolved assemblage of small Atlantic Forest Astyanax distributed across southeastern and southern Brazil. Members of this complex share broadly similar body form and silvery colouration and are diagnosed largely through combinations of meristic counts, body proportions, and geographic distribution. The placement of A. guaricana within Astyanax reflects traditional usage in its original description; broader generic limits across Characidae remain an active area of systematic revision.
Morphology
Astyanax guaricana is a small, moderately deep-bodied characid, reaching a recorded maximum of 4 in standard length. Body depth ranges from 29.3 to 35.7% of standard length, giving adults a somewhat robust profile for the scabripinnis group. Key meristic counts from the original description include 18 to 22 branched anal-fin rays (mean 21), 40 to 43 scales in the lateral line (mean 42), and 15 to 17 circumpeduncular scales.
A diagnostic feature shared with other scabripinnis-complex members is the presence of two vertical humeral spots on the flank behind the opercle — a character useful for placing the species within the complex, though the precise number and distinctness of humeral markings vary among individuals. Males bear small hooks on the anal-fin rays, a sexually dimorphic feature common across Astyanax and useful for sexing preserved or living specimens. Colouration is typical for the genus: silvery flanks with a lateral band, dark pigmentation along the dorsal midline, and a caudal-peduncle spot.
Habitat
Astyanax guaricana is known only from tributaries of the rio Cubatão drainage in eastern Paraná State, southern Brazil, where it inhabits streams flowing through Atlantic Rainforest. The type locality, rio Arraial, feeds the Guaricana Reservoir near São José dos Pinhais — a region of the Serra do Mar escarpment where Atlantic Forest remnants persist alongside agricultural and peri-urban land use. The Cubatão is a coastal drainage running to the Atlantic rather than to the interior Paraná basin, placing this species entirely within the Atlantic Forest biome.
Like other members of the scabripinnis complex distributed across Atlantic Forest streams, A. guaricana presumably occupies clear to lightly turbid, cool, well-oxygenated stream environments with rocky or sandy substrates, riparian cover, and relatively stable seasonal flow. Its restricted known range — only the Cubatão drainage tributaries according to the original description — makes it one of the more localised members of this diverse species complex.
Feeding
No dedicated dietary study of Astyanax guaricana has been published. Members of the scabripinnis species complex are generally opportunistic omnivores, consuming a mixture of aquatic invertebrates, allochthonous terrestrial insects falling to the stream surface, algae, and plant material grazed from submerged surfaces — a broad trophic strategy shared across much of the genus Astyanax.
In the aquarium, closely related Astyanax species accept most standard foods readily: good-quality flake and small pellets, frozen invertebrates such as Daphnia, bloodworm, and brine shrimp, and supplementary vegetable matter. Until specific dietary data for A. guaricana are available, this general characid-omnivore model is the best available guide.
Mating
No direct observation of mating behaviour in Astyanax guaricana has been published. The species belongs to a clade of egg-scattering characids with no parental care, and spawning behaviour follows the pattern typical of the genus: males pursue females into areas of fine-leaved vegetation or submerged roots, where eggs are scattered and fertilised in open water or among plant substrate. Males are distinguished from females by the presence of anal-fin hooks, which may function in stabilising contact during spawning.
Seasonal and environmental cues — water temperature, photoperiod, and rainfall-driven changes in water chemistry — likely govern reproductive activity in wild populations, as documented in related Atlantic Forest Astyanax. In the aquarium, similarly sized Astyanax species are induced to spawn by slight temperature increases, water changes simulating rainfall, and the provision of fine-leaved plants or spawning mops.
Breeding
Astyanax guaricana has not been documented as an established aquarium breeding subject, and specific captive-breeding data are absent from the published record. The general breeding biology of the scabripinnis complex provides the best available template: eggs are small, non-adhesive to weakly adhesive, scattered among fine-leaved vegetation, and number in the dozens to low hundreds per spawning event. Adults provide no parental care and will consume eggs if not removed.
For aquarists attempting to spawn wild-caught or obtained specimens, the approach used for other Astyanax applies: condition a small group in a well-planted or mop-equipped tank, trigger spawning with a modest temperature rise and large water change, and promptly remove adults after spawning is observed. Fry are tiny at hatching and require very fine first foods — infusoria or commercial liquid fry food — before advancing to newly hatched brine shrimp nauplii. Data sparse; captive breeding of this species has not been widely reported.
In the aquarium
Astyanax guaricana is not an established aquarium species; it is a small, range-restricted endemic known primarily from the scientific literature, and it does not appear in the mainstream ornamental trade. Its congeners in the scabripinnis complex are similarly rarely traded, as most are small, silvery, and modest in colour relative to the Astyanax bimaculatus group species more commonly sold as tetras.
Should specimens become available — from field collection or specialist exchange — the appropriate care follows the template for cool-water Atlantic Forest Astyanax: a well-oxygenated, moderately cool aquarium in the low-to-mid 20s Celsius, neutral to slightly acidic soft water reflecting the Atlantic Forest stream chemistry of its range, and a group of six or more to support the schooling behaviour natural to the genus. It is a peaceful fish suited to community setups with similarly sized species. Data on long-term aquarium maintenance of this specific species are sparse.
Conservation
Astyanax guaricana has not been formally assessed by the IUCN Red List; its conservation status is Not Evaluated. Its known distribution is narrow — restricted to tributaries of the rio Cubatão drainage in eastern Paraná, all within the Atlantic Rainforest biome. The Atlantic Forest is one of the world's most biodiverse and most threatened biomes, retaining less than 15% of its original cover, and the stream fauna of coastal Paraná faces ongoing pressure from urbanisation, agriculture, and water extraction in the greater Curitiba–São José dos Pinhais metropolitan region.
The Guaricana Reservoir, into which the type-locality stream flows, represents a modified hydrological environment that may affect local stream conditions and connectivity. For a species known from a limited number of localities in a single small coastal drainage, any significant degradation of riparian vegetation or stream quality poses a genuine threat. A formal conservation assessment and broader surveys to establish the full extent of the species' range would be a valuable step for regional ichthyofaunal conservation planning.