Taxonomy & naming
Hypsolebias stellatus was described by Wilson J. E. M. Costa and G. Brasil in 1994, originally placed in the genus Cynolebias as Cynolebias stellatus Costa & Brasil, 1994b. The species was subsequently reassigned to Simpsonichthys when that genus was erected to accommodate a clade of South American annual killifish previously grouped within the broadly defined Cynolebias. Eschmeyer's Catalog of Fishes is the authority for the valid current combination Hypsolebias stellatus (Costa & Brasil, 1994), with the parenthetical authority denoting the original generic placement.
Costa's 2007 revision of the Simpsonichthys notatus species group, documented in Plazi TreatmentBank, places H. stellatus within that group and distinguishes it from close relatives by a combination of male colour characters: elongated light blue spots with black interspaces on the basal portion of the dorsal fin, and a dark grey distal stripe on the anal fin. The holotype (MNRJ 12446, a male 1.57 in SL) was collected from a temporary pool approximately 1 mi north of the city of São Francisco, Estado de Minas Gerais, Brazil (15°50'S, 44°50'W), at an altitude of roughly 1542 ft above sea level.
This fish was long listed as Simpsonichthys stellatus; Eschmeyer's Catalog of Fishes places the species in Hypsolebias, and the current combination Hypsolebias stellatus is followed here.
Morphology
FishBase records a maximum size of 2.4 in for this species, making it a small to medium killifish consistent with other Simpsonichthys. Sexual dichromatism is pronounced, as is typical for annual killies: males carry elaborate coloration used in rival assessment and mate attraction, while females are cryptically coloured.
Male colouration is described in Costa's 2007 revision as dark yellow-ochre on the sides, overlaid with 9–11 grey vertical bars and scattered light blue iridescent dots. The dorsal fin is dark brownish-red with blue spots; the anal fin is purplish-grey with a dark distal edge. Females are pale with faint grey markings and lack the iridescent patterning. These features, combined with the distinctive elongated blue spots on the basal dorsal fin and the dark grey distal anal-fin stripe in males, are the diagnostic characters separating H. stellatus from other members of the S. notatus group.
Habitat
The species occupies temporary pools within the Cerrado, the vast tropical savanna biome of central Brazil. The middle São Francisco basin in Minas Gerais is characterised by a strongly seasonal climate with a pronounced dry season during which the shallow pools that annual killies inhabit evaporate completely. The type locality sits at approximately 1542 ft elevation, in the semi-arid to sub-humid transition zone that characterises much of the middle São Francisco drainage.
These temporary pools are typically shallow, with soft substrates of peat, mud, and organic detritus — the medium in which the eggs are deposited and undergo diapause. Water chemistry in Cerrado pools associated with annual killies is generally soft and somewhat acidic; hobbyist breeding reports for H. stellatus suggest water temperatures of 68–73 °F and moderately soft, acidic conditions, consistent with Cerrado pool chemistry during the rainy season when fish are active.
Feeding
No species-specific dietary studies appear in the available literature for Hypsolebias stellatus. Annual killifish in general are opportunistic micro-predators, feeding on small invertebrates — aquatic insect larvae, crustaceans, and worms — as well as zooplankton present in the temporary pools they inhabit. The diet reflects what is seasonally abundant in pools that are recolonised at the start of each rainy season and that support dense invertebrate communities before larger predators establish.
In aquarium conditions the species readily accepts live and frozen small invertebrates including Artemia nauplii, daphnia, mosquito larvae, and tubifex. A varied diet maintains colour and condition in males and supports successful egg production in females.
Mating
Hypsolebias stellatus reproduces by the annual killifish spawning mode: paired spawning dives in which the male and female press together and plunge into the soft substrate, depositing a small number of eggs buried in the peat or mud with each dive. This spawning-into-substrate behaviour is characteristic of the South American annual killifish clade and contrasts sharply with the plant-spawning of non-annual killies.
Male colouration — the yellow-ochre base, vertical bars, blue iridescent spots, and ornate dorsal and anal fins — serves as a signal in male-male competition and female mate choice. Females assess and select among displaying males; subordinate males may be excluded from spawning. The intensity of colour in males is likely condition-dependent and reflects competitive quality. Spawning activity in nature is concentrated in the rainy season when pools exist and food is abundant, with pairs spawning repeatedly over the course of weeks before the pool contracts.
Breeding
As an annual species, Hypsolebias stellatus produces diapausing eggs that are buried in the substrate and must survive the complete desiccation of the habitat through the dry season. Eggs enter diapause — an arrested state of embryonic development — that allows them to persist in dry or barely moist substrate for months until rains return and pools refill. This diapause mechanism is the defining adaptation of annual killies and allows the population to persist across years as a buried egg bank rather than as living adults, which die when the pool dries.
In the aquarium, breeding follows the standard annual-killi protocol: a peat or coir spawning medium is placed in the tank, the pair spawns into it over days to weeks, and the medium is then collected, squeezed to remove most moisture, and stored in a sealed container at room temperature for a diapause period of several weeks to a few months before being re-wetted to trigger hatching. Killi.co.uk reports one hobbyist experience with H. stellatus noting breeding at 68–73 °F in moderately soft, acidic water, with spawning rated as relatively easy but yielding a somewhat male-biased sex ratio. Fry should be raised on appropriately sized live foods starting with infusoria or rotifers and progressing to Artemia nauplii.
In the aquarium
Hypsolebias stellatus is an annual killifish suited to killifish specialists who are comfortable with the peat-spawning protocol and dry-storage of eggs. It is not a community aquarium fish: pairs or trios are best maintained in small, species-only setups of 8–16 US gal, with a tightly fitting lid (killies are capable jumpers) and subdued lighting that shows male colour to advantage. Floating plants and fine-leaved vegetation provide cover and reduce aggression.
Water conditions should be moderately soft and slightly acidic (pH around 6.0–7.0, soft to medium hardness) at temperatures of 68–73 °F. Pairs or small groups of females per male are typical; multiple males together will fight. The hobby availability of this species is limited, and it is primarily circulated through killifish club auctions and specialist breeders rather than commercial channels. Maintaining live populations in the hobby is ecologically significant given the restricted natural range of most Simpsonichthys species.
Conservation
Hypsolebias stellatus has not been evaluated by the IUCN Red List and carries a status of Not Evaluated (NE). This is common among narrow-range Cerrado annual killifish: many species are known from single localities or very restricted pool systems, and formal threat assessments have not kept pace with the number of species described.
The Cerrado biome has suffered severe deforestation and agricultural conversion — it is one of the world's most threatened and least protected biodiversity hotspots, with a large proportion of its original vegetation lost to soybean cultivation, cattle ranching, and sugarcane production. Temporary pool habitats used by annual killifish are among the most vulnerable microhabitats: they are easily drained, filled, or degraded by changes in catchment land use, and the fish that depend on them have nowhere to retreat. The middle São Francisco basin faces additional pressure from water extraction for irrigation and from the impacts of the Transposition of the São Francisco River project on the broader catchment hydrology. For a species known from a single type locality near the town of São Francisco, Minas Gerais, these landscape-scale pressures represent a genuine threat to the persistence of the egg bank on which the population depends.