Taxonomy & naming
Simpsonichthys brunoi was described by Wilson J.E.M. Costa and Flávio Brasil in 1994, based on specimens from the ribeirão Canabrava floodplain pools near Vila Boa in Goiás state, central-eastern Brazil. The authority is presented in parentheses — (Costa & Brasil, 1994) — because the species has at various points been reclassified. Costa's 2006 revision of Neotropical annual killifishes elevated Hypsolebias as a genus (or recognised it as a subgenus of Simpsonichthys), and the species has appeared in the literature under the combination Hypsolebias brunoi (Costa, 2006). The Catalog of Fishes continues to track the valid placement; Killi-Data, the primary specialist database for the order Cyprinodontiformes, records the taxonomic notes on this reclassification and the competing arrangements.
The species epithet brunoi honours Bruno Bove da Costa, following the standard practice in killifish taxonomy of naming new species for collectors, researchers, or enthusiasts who contributed to their discovery. The genus Simpsonichthys was established to accommodate a group of South American annual killifishes broadly distributed across the cerrado and caatinga seasonal wetlands of Brazil, a group noted for vivid male colouration and obligate egg diapause.
Morphology
Simpsonichthys brunoi is a small, laterally compressed killifish. FishBase records a maximum standard length of 1 in SL, while It Rains Fishes, citing detailed meristic data, gives up to 1.5 in SL — the latter figure likely reflecting the larger sex. Meristic counts are D 19, A 21. Males display the vivid colouration typical of the genus: iridescent blues, greens, and reds arranged in the flanks and fins in patterns that vary by individual and population, serving as species-recognition cues in the turbid, shallow pools the fish inhabits. Females are considerably less colourful, showing a cryptic brownish or olive ground with little iridescence, as expected for a fish that must remain camouflaged while guarding developing ovaries.
The body form is typical for a burrowing annual killi: moderately deep, with a rounded head, a superior to terminal mouth suited for surface feeding, and posteriorly placed dorsal and anal fins positioned to facilitate rapid forward dives into soft substrate during spawning. The caudal fin is rounded to slightly lanceolate.
Habitat
The species is known from the floodplain pools associated with the ribeirão Canabrava drainage near Vila Boa, Goiás, in the cerrado biome of central-eastern Brazil. These are shallow, seasonal pools that form during the Brazilian wet season (roughly October–March) and dry out completely during the dry season. The substrate is soft — a mixture of fine mud, sand, peat, and accumulated detritus — into which the fish spawns and in which eggs overwinter in diapause.
Cerrado seasonal pools are typically warm and variable in chemistry, often soft to moderately hard with slightly acidic to near-neutral pH reflecting the organic load of decaying vegetation and local soil chemistry. Water temperatures follow the local climate, rising sharply in the wet season when pool levels are high and dropping toward the end of the wet season as pools shrink and concentration effects begin. The pools are generally shallow, well-lit, and rich in aquatic invertebrates during the brief window of water availability.
Feeding
Like all Simpsonichthys species, S. brunoi is a generalised micro-predator in the wild, feeding on the small invertebrates — mosquito larvae, aquatic crustaceans, worms, and other benthic or surface-dwelling invertebrates — that proliferate rapidly in the seasonal pools the fish inhabits. The short growing season of an annual pool favours fast, opportunistic feeding to fuel the rapid growth and early sexual maturation that defines the annual killifish life strategy.
In captivity the fish accepts a range of live and frozen invertebrate foods: artemia nauplii and adults, daphnia, cyclops, and small chironomid larvae (bloodworm) are all suitable. High-quality dried micro-pellets designed for small carnivorous fish are taken by some individuals. Varied feeding accelerates condition and colouration in males.
Mating
Mating in Simpsonichthys brunoi follows the obligate peat-spawning mode universal in the genus. Males are brightly coloured and display actively to females, spreading fins and posturing to show their lateral and dorsal colours. Competition between males is intense — pools are small and male densities can be high — and dominant males may suppress subordinate males through display and chasing.
When a female is receptive, the pair align side-by-side at the substrate surface, then dive together into the soft mud or peat — the male using his body to drive both fish downward. Eggs are fertilised and deposited in the substrate during this brief dive. The fish resurface immediately. A single female may produce multiple eggs over several dive sequences in a session, and spawning occurs repeatedly throughout the wet season as conditions allow. There is no pair bond and no parental care after spawning.
Breeding
Simpsonichthys brunoi is an obligate annual killifish: the eggs it buries in substrate must pass through a diapause period before hatching. It Rains Fishes documents a diapause duration of 8–10 weeks under peat storage conditions in the hobby — hobbyists collect the peat containing eggs, partially dry it, and store it sealed in plastic bags at moderate temperature for that period before re-wetting to trigger hatching. In the wild the diapause period corresponds to the complete drying of the pool through the dry season and the resumption of rains.
Once re-wetted and hatched, fry are relatively large and free-swimming from the outset, able to take artemia nauplii almost immediately. Growth is rapid: It Rains Fishes records sexual maturity and the production of first eggs as early as 5–6 weeks after hatching. Wild lifespan is tied to the duration of pool water availability and is typically 6–12 months; captive individuals can live 10–12 months. This compressed lifecycle is the fundamental adaptation of annual killifishes to temporary habitats.
In the aquarium, spawning medium is typically a layer of boiled, tannin-leached peat moss or commercial coconut coir placed on the tank floor. Pairs are placed over this medium; spawning occurs within days to weeks. After a spawning period, the medium is removed, gently squeezed but not dried completely, sealed, and stored for 8–10 weeks before being placed in a shallow tray of soft, slightly acidic water to trigger hatching.
In the aquarium
Simpsonichthys brunoi is a specialist-level fish suited to experienced killifish keepers rather than general community aquaria. A small, densely planted species tank of 5.5–10 US gal is appropriate for a breeding trio or pair; multiple males will quarrel in close quarters. The aquarium should be tightly covered, as killies are accomplished jumpers. Soft, slightly acidic to neutral water that approximates the chemistry of Brazilian cerrado pools is preferred — very soft, low-conductivity water at pH 6.0–7.0 and temperatures of 72–79 °F suits the species well.
A layer of peat or coir substrate at least 2 in deep is essential to allow natural spawning behaviour. Dense surface vegetation or floating plants provides cover, reduces aggression, and brings out bolder male display. The fish are short-lived; a keeper should maintain a peat storage programme to carry eggs through diapause and renew the population from each generation's eggs.
Simonichthys brunoi is rarely encountered in mainstream aquarium retail and is primarily kept and exchanged within specialist killifish societies and clubs, where eggs in peat are the standard unit of trade — a practical adaptation to the fish's own biology.
Conservation
The IUCN Red List assesses Simpsonichthys brunoi as Vulnerable under criterion D2, meaning its extent of occurrence is so small that the species could qualify for a higher threat category in a short period under plausible threats. The assessment date is recorded by FishBase as 2018-11-07. The species is known only from the ribeirão Canabrava floodplain pools near Vila Boa, Goiás — a single restricted locality in the Brazilian cerrado.
The cerrado is one of the world's most threatened biomes. Agriculture — particularly large-scale soybean and cattle farming — has cleared and drained vast areas of cerrado savannah, including the seasonal wetland systems on which annual killifishes depend. The temporary pools inhabited by S. brunoi are vulnerable to drainage for irrigation, infilling for agricultural expansion, alteration of the local hydrology through upstream channelling, and pollution from agrochemical run-off. The introduction of invasive fish species — including Nile tilapia and various livebearers widely used as mosquito-control agents — into formerly fish-free seasonal pools poses an additional direct threat, as predation on fry and adults can eliminate killifish populations rapidly.
Conservation of this species depends on the protection and maintenance of intact cerrado seasonal wetlands within its extremely restricted range. It is not known to occur in any protected area. Ex-situ maintenance by specialist killifish hobbyists and societies, who sustain captive populations through peat-egg exchange, represents a meaningful backup against wild population collapse.