Taxonomy & naming
Maratecoara formosa was described by Wilson J. E. M. Costa and Brasil in Costa (1995), with the type locality in the middle Tocantins River basin in central Brazil. The Catalog of Fishes (Eschmeyer, Fricke & van der Laan) records the valid name as Maratecoara formosa Costa & Brasil in Costa, 1995. The authority appears without parentheses because the species has remained in the genus Maratecoara since its original description and has not been transferred.
The genus Maratecoara belongs to the tribe Cynolebiatini within the family Rivulidae, the New World killifishes. It is a small genus of South American annual killifishes from the central Brazilian Cerrado, closely related to genera such as Hypsolebias and Cynolebias. The specific epithet formosa is Latin for 'beautiful' or 'well-formed', a reference to the species' ornamental coloration, particularly in males.
Morphology
Maratecoara formosa is a small fish reaching a maximum total length of approximately 2 in (FishBase). Like other cynolebiatine annuals, it has a robust, slightly compressed body suited for burrowing into substrate during spawning. Standard length proportions recorded in the hobbyist literature give body depth at 37.7% of standard length, pre-dorsal distance at 64.9% of standard length, and lateral-line scale count averaging 26.5.
Males are the more visually striking sex, displaying vivid coloration and performing elaborate gill-cover displays during courtship. Females are typically less colourful, with more cryptic patterning suited to the role of substrate selection during spawning. Sexual dimorphism is thus clear, with males showing the intensified hues and display behaviours characteristic of annual killies in the tribe Cynolebiatini.
Habitat
Maratecoara formosa is native to the middle Tocantins River basin in the Brazilian state of Goiás and Tocantins. Documented collection localities include Formosa (Goiás state) and Brejinho de Nazaré (Tocantins state), from which three collection locations have been formally recorded. The species inhabits seasonal lagoons and shallow pools in the Cerrado, the vast tropical savannah biome of central Brazil characterised by a strongly seasonal climate with a pronounced dry season.
These pools are temporary, typically filling during the rainy season (November to March) and drying completely during the winter dry season. The water in Cerrado pools is commonly warm and soft, often somewhat turbid with suspended organic matter. The fish are adapted to the full seasonal hydrological cycle of their habitat — filling, peak productivity, and complete desiccation — and cannot persist in perennial water bodies in the same way as non-annual species.
Feeding
As a small-bodied carnivore, Maratecoara formosa feeds primarily on small invertebrates in the wild. The seasonal pools it occupies are rich in zooplankton, small aquatic insects, and crustaceans during the wet season, providing the dense prey base that annual killies exploit to complete their rapid growth and reproduction before the water disappears.
In the aquarium, annual killies in this group accept live and frozen foods readily. The hobbyist literature for this species specifically recommends live food during the breeding period, when males and females are being conditioned for spawning. Brine shrimp nauplii (Artemia), micro-worms, Daphnia, and small chironomid larvae are all appropriate. Providing a variety of live and frozen meaty foods is standard practice for maintaining peak condition in annual Cynolebiatini.
Mating
Maratecoara formosa is a substrate-spawning annual killifish. Males are reported to engage in colourful gill-cover displays during courtship — a behaviour well-documented in the genus and in closely related South American annual killies. These lateral and frontal displays allow females to assess male quality before committing to a spawning dive.
Once a pair has formed, spawning follows the typical cynolebiatine pattern: both fish dive together into the soft muddy or peaty substrate, where eggs are deposited in small groups rather than singly. The eggs are not scattered freely into the water column but are actively buried, which protects them from predation and, crucially, places them in the substrate where they can survive desiccation when the pool dries. A dark aquarium environment is preferred, consistent with the species' association with shaded or turbid forest-edge Cerrado pools.
Breeding
Maratecoara formosa is a true annual killifish with diapausing eggs. After spawning, the eggs remain buried in the substrate and enter embryonic diapause — a state of arrested development that allows them to survive the months-long dry season during which the parent pool is completely dry. The adults die with the drying of the pool; the entire population overwinters as buried eggs.
In the aquarium hobby, this species is bred on a peat moss or coconut coir substrate. Adults spawn into the medium over several weeks, after which the medium is removed, gently squeezed to remove excess water, and sealed in a plastic bag or container to begin the dry storage period. Incubation temperature and duration affect hatching timing: the hobbyist literature for this species records incubation periods of three to five months or longer at 75–82 °F, shortening to a faster schedule at 86–91 °F. When the storage period is complete, the peat is re-wetted and the fry emerge within hours to days. Newly hatched fry are large enough to take Artemia nauplii from day one, an advantage in the hobby for rapid grow-out. Growth to sexual maturity is fast, consistent with the compressed annual life cycle.
In the aquarium
Maratecoara formosa is maintained by specialist annual killifish keepers, particularly within the American Killifish Association (AKA) community, where it is catalogued as a Class 3 South American Annual. The species has been written about in the AKA's Journal (JAKA) on at least 13 occasions, suggesting a reasonable history in the hobby despite its relative rarity compared to more widely traded species.
The aquarium setup follows standard practice for small cynolebiatine annuals: a small, dimly lit tank with a soft, deep peat or coco-peat substrate for spawning, and tannin-rich soft water. A dark background and floating plants or surface cover help replicate the shaded, turbid conditions of Cerrado seasonal pools. The species should be kept in pairs or small groups, with males displaying but generally not causing injury at low stocking densities. Water temperature in the range of 75–82 °F is appropriate. Live foods are recommended for conditioning and for optimal breeding results. Because the fish are annual, keepers plan the wet-storage and dry-storage cycle in advance to synchronise egg collection and hatching with the keeper's schedule.
Conservation
The IUCN Red List assessed Maratecoara formosa as Vulnerable (VU) in 2018 (assessment authority: Instituto Chico Mendes de Conservação da Biodiversidade, ICMBio). The assessment reflects the species' narrow endemic range within the middle Tocantins basin and the severe and ongoing degradation of the Cerrado biome.
The Cerrado is one of the world's most threatened biodiversity hotspots. Its seasonal wetlands and vereda palm-swamp systems — the very habitats that support annual killifishes like M. formosa — have been lost at an extraordinary rate to soybean agriculture, cattle ranching, and large-scale water management including dam construction on the Tocantins River itself. For a species with only three documented collection localities, the loss or degradation of even one pool can represent a significant fraction of the total wild population. The species' annual life history, while resilient to natural drought, provides no buffer against permanent habitat loss — there is no perennial adult population to recolonise a restored habitat, making egg bank preservation and hobbyist breeding programmes a meaningful complement to in-situ conservation efforts.