Taxonomy & naming
Maratecoara splendida was described by Wilson J.E.M. Costa in 1995 and is placed in the family Rivulidae within the order Cyprinodontiformes. The genus Maratecoara was erected to accommodate a small group of plesiolebiasine killifishes from the seasonal savannahs of central Brazil; Costa's 2007 revision in Zootaxa (1410: 1–41) consolidated the taxonomy of Maratecoara alongside the related genera Pituna and Plesiolebias, and remains the primary systematic reference for the group. Eschmeyer's Catalog of Fishes records the valid name as Maratecoara splendida Costa, 1995.
The genus name Maratecoara is a Brazilian toponym derived from the Aruana/Goiás region, honouring the geographic heartland of the genus. The specific epithet splendida is from the Latin splendidus, meaning brilliant or resplendent, alluding directly to the vivid iridescent colouration of males in breeding condition — a characteristic that immediately distinguishes this species from the more soberly patterned members of its genus.
Within the plesiolebiasine killifishes, Maratecoara represents a lineage adapted to the seasonal pools and gallery-forest streams of the Cerrado, the vast Brazilian interior savannah. The group shares the defining annual life-history strategy of Neotropical killifishes tied to habitats that disappear on a yearly cycle.
Morphology
Maratecoara splendida is a sexually dimorphic, elongate killifish of modest size. Males reach a maximum of approximately 1.5 in standard length; females are somewhat smaller, reaching roughly 1 in SL (FishBase). This places the species among the genuinely miniature South American annuals, comparable in scale to the smallest members of Notholebias and Spectrolebias.
Males in breeding condition are the sex for which the epithet splendida was coined. The flanks display a vivid iridescent pattern — typically an interplay of blues, greens, and reds over a dark ground — that is characteristic of the group and serves as a signal during the male territorial and courtship displays. Fins are pigmented and often carry extension of the colour pattern into the caudal and dorsal rays. Females, as is typical for annual Rivulidae, are cryptically coloured in brownish or olive tones with minimal patterning, an adaptation that reduces predation risk while they are engaged in substrate-spawning.
The body plan is cylindrical and slightly compressed — a shape suited to burrowing behaviour in soft substrates. The mouth is small and upturned, positioned for surface and mid-water prey capture in shallow seasonal pools.
Habitat
The known range of Maratecoara splendida is restricted to the type locality: a seasonal lagoon in the vicinity of the rio Canabrava, a tributary of the upper Tocantins drainage in the state of Goiás, Brazil (FishBase; IUCN 2018). The Tocantins basin drains the eastern Cerrado, the world's most biodiverse tropical savannah, a landscape characterised by a pronounced dry season lasting five to six months during which temporary wetlands — veredas, campos de murundus, and shallow lagoons — contract, fragment, and ultimately disappear.
Maratecoara splendida inhabits these seasonal lagoons during the rainy season (roughly October to March), when rainfall refills the pools and triggers hatching of diapausing eggs. The water in Cerrado seasonal wetlands is typically warm, shallow, and soft, often stained by organic matter from surrounding vegetation; the aquarium literature records conditions of approximately 77 °F and near-neutral pH for related annual species of the region. Substrate is the key habitat element: a layer of soft mud, peat, or accumulated organic detritus into which the fish spawn.
Beyond the type locality, the distribution of this species has not been confirmed at additional sites, making it one of the most geographically restricted killifishes in South America. The IUCN notes that the geographic range is extremely limited and that the population trend is unknown.
Feeding
Like other small plesiolebiasine killifishes, Maratecoara splendida is a microinvertebrate predator in the wild. In seasonal Cerrado pools it would encounter zooplankton, small aquatic insects, midge larvae, and other invertebrates that bloom abundantly during the wet season — the same prey pulse that fuels the rapid growth and reproduction of annual killifishes before the pools dry.
In the aquarium, annual killifishes of this size group are best maintained on live or frozen small invertebrates: Artemia nauplii, Daphnia, Moina, micro-worms, and bloodworm. Dry foods can be accepted by established adults but live and frozen items maintain condition, encourage spawning, and keep the gut functioning normally. Feeding several small portions per day rather than one large meal suits the continuous opportunistic foraging mode of these fish in nature.
Mating
Maratecoara splendida is an annual killifish and an obligate substrate-spawner. Courtship is initiated by the male, who displays his full chromatic brilliance in front of the female through lateral presentation and head-shaking movements (ForAquarist.com breeding guide). These displays advertise male quality and stimulate female receptivity; in densely planted or structured aquaria, subdominant males are driven off while the dominant male courts.
Once a female is receptive, the pair align side by side and the male curves his body around hers in the characteristic diving embrace of annual killifishes. Together they plunge briefly into the soft substrate — peat, mud, or detritus — depositing and fertilising one or a few eggs per dive before surfacing. This sequence is repeated across multiple spawning acts over the course of hours or days. The eggs are sticky and are left adhered to or buried within the substrate without any further parental investment.
In the wild this mating behaviour is compressed into the wet season window; a single season may be the complete lifetime of the adults. In the aquarium, providing a layer of moist peat or coconut coir of sufficient depth — at minimum 2–3 in — is essential for the fish to perform the spawning dive successfully.
Breeding
The eggs of Maratecoara splendida, once deposited in the substrate, enter a state of arrested development known as diapause. In the wild, the drying of the pool over the dry season triggers or deepens diapause; the embryos remain viable within the desiccated substrate for weeks to months until the rains return and the pool refills, at which point the eggs complete development rapidly and hatch. This diapausing strategy is the defining adaptation of annual killifishes and the foundation of the hobby's peat-storage technique.
In aquarium practice, the spawning substrate is periodically collected and placed in sealed plastic bags or containers in barely moist condition at room temperature. After an incubation period that varies by species and temperature — typically two to four months for South American annuals of this group — the substrate is re-wetted with soft, slightly acidic water, and fry hatch within hours to a day or two. Fry of small plesiolebiasines like Maratecoara splendida are tiny and require appropriately sized first foods: freshly hatched Artemia nauplii, micro-worms, or commercial fry food, offered from day one. Growth is fast; fish can reach sexual maturity in as little as four to six weeks under warm conditions, reflecting the selective pressure of an environment that grants only one season for growth, reproduction, and egg-deposition before the pool dries.
The ForAquarist.com breeding guide notes that consistent, generous feeding — including live tubifex — is particularly important for maintaining spawning activity in annuals of this group, and that the species does not necessarily dive into the substrate but deposits eggs at or near its surface, so a shallower peat layer may suffice relative to deep-diving South American annuals.
In the aquarium
Maratecoara splendida is a specialist's fish, suited to the killifish hobbyist rather than the general community keeper. Its small size (males under 1.5 in), rapid life cycle, and requirement for a peat or coir spawning substrate make it best housed in a dedicated species or genus tank. A small, shallow aquarium of 5.5–10 US gal is adequate for a pair or small group; water depth need not exceed 6 in. Subdued lighting, dark substrate, and the addition of floating plants or other surface cover reduce stress and encourage natural behaviour.
Water conditions should replicate the warm, slightly soft, near-neutral waters of the Cerrado seasonal lagoon: temperature around 72–79 °F, pH approximately 6.5–7.5, and low to moderate hardness. The ForAquarist.com guide records 77 °F and pH ~7 as suitable starting parameters. A gentle sponge filter provides adequate circulation without disturbing the spawning substrate layer. Males will spar but serious injury is rare in a well-structured aquarium; a single male paired with one or two females is the usual approach.
Spawning substrate — commercial peat, coconut coir, or fine aquatic sand — should be provided at the bottom of the tank in a layer of at least 2–3 in. Eggs can be collected by removing and partially drying the substrate every two to four weeks, then storing it sealed until the incubation period is complete. Given the species' extremely restricted wild distribution and Vulnerable status, captive colonies maintained by the killifish hobby represent a meaningful genetic reservoir. The American Killifish Association (AKA) supports conservation-minded breeding programs for threatened annual species.
Conservation
The IUCN Red List assessed Maratecoara splendida as Vulnerable (VU) in November 2018, the assessment driven by the extreme restriction of its geographic range to a single seasonal lagoon in the rio Canabrava drainage, upper Tocantins basin, Brazil. The population trend is listed as unknown, reflecting the near-total absence of systematic survey data for this remote and ephemeral habitat type.
The primary threats identified by the IUCN assessment are agriculture and aquaculture, specifically livestock farming and associated wetland degradation. The Cerrado — the biome within which Maratecoara splendida occurs — is one of the most threatened tropical ecosystems on Earth. It has lost more than half of its original extent to agricultural conversion, principally soy and cattle farming, and continues to be cleared at a rate among the highest of any major biome. Seasonal lagoons and veredas are particularly vulnerable: they are drained for pasture improvement, used as livestock watering points, and degraded by cattle trampling and waste loading. A species confined to a single such lagoon has no fallback population.
Conservation actions recommended by the IUCN include land and water protection and resource and habitat protection, but no protected area currently encompasses the type locality with certainty. The American Killifish Association and the broader European killifish hobby have a role to play: captive-bred populations of Maratecoara splendida maintained under documented collection data represent both a genetic reservoir and a research resource should future reintroduction or habitat restoration become possible.