Taxonomy & naming
Hypsolebias notatus was described by Costa, Lacerda & Brasil in 1990, with the type locality recorded as a temporary pool at Alvorada do Norte, Goiás state, central Brazil (approximately 14°30'S, 46°50'W, altitude around 1608 ft), situated within the Rio Paranã drainage of the upper Tocantins basin. The holotype — a male of 0.99 in standard length, catalogued as MZUSP 39985 — is held at the Museu de Zoologia da Universidade de São Paulo. Eschmeyer's Catalog of Fishes treats the valid name as Hypsolebias notatus (Costa, Lacerda & Brasil, 1990), placed within the family Rivulidae (South American annual killifishes).
The species was reclassified in some older literature under the genus Hypsolebias, a name encountered in collection databases; the current Catalog of Fishes treatment restores it to Simpsonichthys. A 2004 revision by Costa & Brasil (Zootaxa 737) formally recognised a H. notatus species group — a clade that also includes S. stellatus, S. similis, S. rufus, S. trilineatus, S. auratus, and S. ocellatus, among others — confirming H. notatus as the anchor taxon of a recognised and species-rich lineage within the genus.
This fish was long listed as Simpsonichthys notatus; Eschmeyer's Catalog of Fishes places the species in Hypsolebias, and the current combination Hypsolebias notatus is followed here.
Morphology
Males reach a maximum of approximately 1.32 in standard length (FishBase records 1.32 in SL as the upper figure for this species). The body plan is typical of the genus: moderately deep-bodied, laterally compressed, with a rounded caudal fin and a slightly upturned mouth suited to surface and mid-water feeding.
Sexual dimorphism is pronounced in both colour and finnage. Males are dark yellow-ochre on the flanks, overlaid with vivid blue iridescent dots and irregular bars that shift in intensity under changing light — an advertisement display directed at both potential mates and rival males. Females are plain: light brownish-grey with diffuse dark spotting, a cryptic colouration that affords concealment among leaf litter and detritus on the pool floor. Fin shapes also differ; males develop extended, ornate dorsal and anal fins relative to females.
Habitat
The native range of Hypsolebias notatus is confined to the Rio Paranã drainage within the upper Tocantins River basin, Goiás state, central Brazil — a region dominated by the Cerrado biome, the vast tropical savanna that constitutes one of the world's recognised biodiversity hotspots. The species inhabits small temporary pools that form on the savanna floor during the wet season (roughly October–March) and evaporate entirely in the dry season.
These pools are typically shallow, nutrient-enriched, and heavily vegetated with aquatic grasses and marginal sedges. Water conditions recorded at the type locality and related Cerrado pools are near-neutral (FishBase lists pH 7.0 for the species) and warm, reflecting the high ambient temperatures of the Goiás plateau. The pools sit at an altitude of roughly 1608 ft, placing them in the central Cerrado tablelands rather than in lowland Amazonian floodplains. Because the pools dry completely, the fish cannot survive the dry season in water — the entire resident population perishes, and survival of the species depends entirely on the diapausing eggs buried in the substrate.
Feeding
Hypsolebias notatus is an opportunistic micro-predator, as is typical of rivulid killifishes. In the wild it takes small invertebrates available in the temporary pool environment: mosquito larvae, midge larvae (chironomids), small crustaceans, and zooplankton are the principal prey items. The relatively small terminal mouth is well suited to picking individual prey from the water column or from the surface film.
In the aquarium the species accepts a wide range of live and frozen small invertebrates — Daphnia, Artemia nauplii, bloodworm (Chironomus larvae), and micro-worms — as well as high-quality dried foods sized appropriately for a fish of under 1.38 in. Live foods are preferred for conditioning breeders and for maximising colour expression in males. Overfeeding should be avoided; the pools these fish inhabit in nature, while productive, are not permanently food-rich, and excess waste quickly degrades the water quality of the small volumes typically used in annual killifish husbandry.
Mating
Like all members of the genus Simpsonichthys, H. notatus is an annual killifish with a bottom-spawning reproductive strategy driven by the predictable drying of its seasonal pool habitat. Males are actively territorial and court females with intense lateral displays, fanning their patterned flanks and fins to showcase the blue iridescent markings that distinguish them from cryptic females and from rival males.
When a female is receptive, the pair engage in a spawning dive — the 'deep diving' behaviour characteristic of South American annual killies in the hobbyist literature. The male presses alongside the female and the two submerge together into the soft substrate (peat, mud, or organic detritus on the pool floor), where one or a few eggs are deposited with each dive. Multiple dives occur across a spawning session, and a single pair may produce eggs over many days of the wet-season period before the pool begins to contract.
Breeding
The buried eggs of Hypsolebias notatus are drought-resistant, entering a state of arrested development (diapause) as the pool dries around them. This diapause is not a single fixed stage but can pass through several developmental arrest points — a strategy that spreads hatching risk across time and insures against a false-season pool refill that drains before fry can mature. Eggs remain viable in the dry substrate for the duration of the dry season, which in central Goiás typically lasts several months.
Hatching is triggered by the return of rain and the re-flooding of the pool. Fry are born at a relatively advanced developmental stage compared to non-annual killifishes and begin feeding almost immediately. The life cycle is compressed: in nature, fish grow to sexual maturity, spawn extensively, and then die as the pool dries, all within a single wet season of a few months.
In the aquarium, the standard approach for South American annual killies applies. Spawning medium is a layer of peat, coir, or fine sand-peat mix into which the pair dive. Eggs are harvested periodically, gently pressed to remove excess moisture, and stored in sealed plastic bags or containers at around 75–79 °F for a diapause period of typically 3–4 months, after which the medium is re-wetted to trigger hatching. Fry are raised on infusoria and micro-worm before graduating to Artemia nauplii. A tight-fitting lid is essential, as even small killifish are capable jumpers.
In the aquarium
Hypsolebias notatus is a species for the specialist annual killifish keeper rather than the general community aquarist. Its small size — under 1.38 in SL — and short captive lifespan (typically one to two years in a well-managed aquarium) mean it requires a dedicated approach based on an understanding of the annual life-cycle husbandry model.
A species tank of 8–11 US gal is sufficient for a pair or a small group of one male and two or three females. Décor should replicate the shallow, heavily planted Cerrado pool: a dark substrate of peat or fine sand mixed with leaf litter, Java moss or other fine-leaved plants, and subdued lighting that shows male colouration to advantage without causing stress. Water should be soft to moderately hard and near-neutral (pH close to 7.0, temperature 72–79 °F), with gentle filtration — a small sponge filter is ideal since strong currents are absent from the seasonal pools these fish inhabit.
The species is best kept separately from robust or nippy tankmates; its small size and the males' extended finnage make it vulnerable in mixed-species setups. Within a trio or group, the single male may harass females persistently; having multiple females distributes this pressure. Annual killies are best approached as a managed cycle: spawn the adults, raise and store eggs through diapause, hatch the next generation, and begin again.
Conservation
The IUCN Red List assesses Hypsolebias notatus as Endangered (EN), a status that reflects the severe constraints imposed by its extremely limited native range within the Cerrado of central Brazil. The species is known primarily from the Rio Paranã drainage in Goiás, and its dependence on small, isolated temporary pools makes it acutely sensitive to any modification of those water bodies or their surrounding catchments.
The Cerrado is among the most threatened biomes on Earth. Identified as a global biodiversity hotspot, it has lost more than half of its original extent to conversion for agriculture — principally soy and cattle ranching — with the Goiás plateau at the heart of this transformation. Temporary pools in agricultural landscapes are frequently drained, filled, or poisoned with agrochemical run-off; the shallow depressions that annual killies require are among the first features eliminated in land clearance. Sedimentation from deforested catchments alters the pool substrate on which eggs are laid, potentially disrupting the burial and diapause of eggs. Introduced Poecilia reticulata (guppies) and other exotic species that persist in partially permanent water bodies pose additional pressure where water management has altered the drying regime.
Conservation of H. notatus depends on the protection of the remaining temporary pool complexes within the Rio Paranã basin and the maintenance of native Cerrado vegetation in their catchments. The hobbyist killifish community — through organisations maintaining living populations and managed egg banks — plays a documented role in preserving captive genetic diversity of threatened annual species, providing a buffer against extinction of wild populations.