Taxonomy & naming
Acrolebias carvalhoi was first described by George S. Myers in 1947, making the authority (Myers, 1947). The Catalog of Fishes (Eschmeyer, Fricke & van der Laan) records the valid combination as Acrolebias carvalhoi, placing the species within the genus Austrolebias Costa, 1998 — the large South American annual killifish genus that encompasses the majority of Argentine, Uruguayan, southern Brazilian, and Paraguayan seasonal-pool killies. Some older literature and FishBase cross-references attribute the species to the junior synonym Acrolebias, reflecting a nomenclatural history common to many Austrolebias taxa before the genus-level revision stabilised current usage.
Austrolebias belongs to the family Rivulidae (South American rivulines), the dominant annual-killifish lineage on the continent. The genus is characterised by its peat-spawning, soil-burrowing reproductive mode and by the highly sexually dimorphic colour patterns found in most species: males carry vivid lateral markings and elongated fin rays, while females are cryptically coloured. Acrolebias carvalhoi is a small-bodied species within the genus, consistent with its ephemeral, resource-limited pool habitat.
The type locality is Porto União, Santa Catarina, Brazil, at the upper limits of the Paraná drainage. No subspecies or geographic variants have been formally described.
This fish was long listed as Austrolebias carvalhoi; Eschmeyer's Catalog of Fishes places the species in Acrolebias, and the current combination Acrolebias carvalhoi is followed here.
Morphology
Acrolebias carvalhoi is a compact, deep-bodied annual killifish reaching a maximum of 1.5 in standard length (FishBase). This places it among the smaller members of the genus. As in all Austrolebias, the species is strongly sexually dimorphic: males carry the vivid lateral patterning and extended dorsal and anal fin rays typical of the genus, while females are cryptically brownish with rounded, shorter fins — an adaptation to reducing predation risk during the vulnerable egg-deposition phase.
The body form is typical of small-pool annual killies: laterally compressed, with a large, upturned mouth suited to surface and mid-water prey capture, and a relatively deep body profile. The fins of breeding males are often edged with iridescent colour. Precise scale counts and meristic data for this species remain sparsely published in the accessible literature; the species is known primarily from its type locality and has not been extensively studied morphometrically.
Habitat
Acrolebias carvalhoi inhabits seasonal freshwater pools in the upper Paraná River basin, centred on the Porto União area of Santa Catarina state, southern Brazil. These are temporary, often shallow bodies of water — grassland pools, flooded depressions, and roadside ditches — that fill with seasonal rains and dry out completely during the dry season. Such habitats are characteristic of the campos sulinos (southern grasslands) biome, where alternating wet and dry seasons drive the annual cycle on which the species depends.
Water conditions in these pools tend to be soft and slightly acidic. FishBase records a temperature of approximately 77 °F and pH 6.5 with low hardness (around 5 dGH), consistent with the soft, poorly buffered rainwater pools typical of the region. The benthos is typically composed of organic detritus, leaf litter, and soft mud or peat — the substrate in which eggs are buried.
Because the pools are ephemeral, the fish's distribution is tightly tied to the annual hydrological pulse: adults are present only when surface water exists, and the species persists through the dry season exclusively as buried, diapausing eggs. The restricted geographic range — confined to the upper Paraná system in Santa Catarina — means that even localised habitat changes can affect the entire known population.
Feeding
Acrolebias carvalhoi is insectivorous, as is typical for annual killies of its size and habitat. In seasonal pools, the available prey base includes aquatic insect larvae (chironomids, mosquito larvae), small crustaceans, and zooplankton; the upturned mouth of Austrolebias is well suited to ambushing prey at or near the water surface. The AKA (American Killifish Association) characterises the diet of this species as insectivorous.
In the aquarium, Acrolebias carvalhoi and its congeners are routinely maintained on live or frozen invertebrates — daphnia, artemia, bloodworm, and tubifex — supplemented with small pellet or flake foods. Like most annual killifish, the species feeds eagerly and grows rapidly, consistent with its short wild lifespan of less than one year.
Mating
Mating in Acrolebias carvalhoi follows the annual killifish pattern characteristic of all Austrolebias: pair-forming courtship between a colourful male and a dull-coloured female, culminating in repeated spawning dives into the substrate. Males actively court females through lateral display, spreading and vibrating the dorsal and anal fins to present their iridescent markings at close range. Receptive females are led by the male to a soft area of the pool floor.
At each spawning event, the male presses alongside the female and both fish drive together into the soft mud or peat substrate, burying several millimetres below the surface. Eggs are released and fertilised within the substrate during this plunge. The pair surfaces and may dive again multiple times over a single session. This spawning behaviour is not incidental — it is the mechanism by which eggs are physically deposited in the diapausing microenvironment they require to survive the dry season. Males are persistent and may harass females if kept in close confinement, so providing visual breaks in the aquarium is important.
Breeding
Acrolebias carvalhoi is a true annual killifish whose eggs undergo diapause — a phase of arrested embryonic development — during the dry season. Research on the Austrolebias genus (PubMed, PLoS ONE) has shown that annual rivuline embryos can enter up to three distinct diapause stages (I, II, and III), with diapause III representing deep metabolic shutdown accompanied by structural stress-response proteins and a near-complete cessation of development. This arrest can persist for weeks to months in dried substrate, allowing embryos to survive conditions lethal to all free-living organisms in the pool.
In the hobby, the standard protocol mimics this cycle: a spawning medium of peat moss or coconut coir fibre is placed on the aquarium floor for several weeks while the pair spawns freely into it. The medium is then removed, gently pressed to remove excess water (but not dried fully), sealed in a plastic bag or container, labelled with the date, and stored in a warm, dark place for a species-appropriate incubation period — typically two to four months for Austrolebias, though the minimum viable period varies by species and batch. After incubation, the peat is tipped into a shallow container and rainwater or soft, slightly acidic water is added; fry hatch within hours to a day.
Newly hatched fry are robust compared to many killifish and can take baby brine shrimp nauplii from day one. Growth is rapid; fish may reach sexual maturity in six to eight weeks under good conditions. Wild fish complete their entire reproductive lifespan within the months the pool holds water, dying as it dries — the next generation exists solely as eggs in the soil until the rains return.
In the aquarium
Acrolebias carvalhoi is maintained by specialist killifish keepers rather than the general aquarium trade, owing to its small size, annual life cycle, and limited availability. A modestly sized aquarium of 8–16 US gal is adequate for a pair or trio; the tank should be well covered, as killifish are capable jumpers. Water should be soft and slightly acidic to reflect the species' natural pool chemistry — pH around 6.0–6.8, low hardness, temperature around 72–77 °F. Subdued lighting and a dark substrate or leaf litter layer reduce stress and encourage natural behaviour.
The substrate must include a spawning medium: peat moss fibre or commercial coconut coir, placed in a tray or loose on the floor to a depth of several centimetres. The fish will spawn spontaneously into this medium once settled. Tankmates are not recommended — annual killies are best kept as single-species setups, particularly given the need to manage the peat substrate and the pair's breeding cycles carefully.
Males can be aggressive toward each other and persistent in their pursuit of females; providing multiple females per male and visual cover reduces harassment. The fish are short-lived by design — expect a lifespan of eight to eighteen months under aquarium conditions, depending on temperature and husbandry. The hobby value lies in the annual cycle itself: the ritual of the peat harvest, incubation, and hatching is a distinctive and rewarding part of keeping annual killies.
Conservation
Acrolebias carvalhoi is assessed as Critically Endangered (CR) on the IUCN Red List (assessment 2018). The species qualifies under criteria reflecting a severely restricted range and ongoing decline — it is known from the upper Paraná River basin in Santa Catarina, Brazil, and its habitat of seasonal grassland pools is under pressure from agricultural conversion, drainage, and the intensification of land use across southern Brazil's campos sulinos.
The ephemeral pool habitats that annual killies occupy are among the least protected freshwater ecosystems in South America. Because they hold water only seasonally, they are routinely overlooked in conservation planning focused on permanent water bodies and are highly vulnerable to drainage for agriculture, cattle grazing disturbance, and road construction. The restricted type locality of Porto União and the very limited documented range of A. carvalhoi mean that even localised habitat destruction could extirpate the entire species. The SHOAL Conservation group has identified this species as a priority fish target, reflecting international recognition of its precarious status.
No captive conservation programme for A. carvalhoi is known to be formally established, though the species is maintained in small numbers within the killifish hobby. The ease with which annual killies can be kept and their eggs stored as dried peat makes ex situ preservation theoretically accessible, but sustained, coordinated action has not been documented for this species. Effective conservation requires protection of the remaining seasonal pool habitat in the upper Paraná system and formal survey work to establish the current extent of the species' range and population size.