Taxonomy & naming
Moema pepotei was described by Wilson J. E. M. Costa in a contribution published in the Revista Brasileira de Biologia (vol. 52, no. 4, p. 621, fig. 6), issued in late 1992 but dated 1993 in most citation practice — hence the authority is written as Costa, 1993. The type specimen is holotype CAS-SU 63604, a male of 2 in SL collected at Forte Príncipe da Beira on the Bolivian border in Rondônia state, Brazil, placing the type locality firmly in the río Guaporé basin of the upper Río Madeira drainage. Eschmeyer's Catalog of Fishes is the authority for the valid name Moema pepotei (Costa, 1993); the parenthetical authority form applies because the species has not been moved from the originally erected combination.
The genus Moema was erected in 1989 with Moema piriana as its type species, and now comprises approximately twenty valid species distributed across temporary-pool habitats of the Amazon basin and the adjacent upper Paraguay drainage. A 2022 phylogenetic study (Drawert et al.) examining related Moema species confirmed the genus as a coherent, monophyletic annual killifish lineage within the broader South American aplocheiloid radiation. Moema is placed within the family Rivulidae (or Cynolebiidae, depending on the classification followed), the South American annual killifishes — a group defined by the diapause-egg life history tied to seasonally drying pools.
The specific epithet pepotei is not explained in the original description in terms available in the cached sources; it may be a local or indigenous toponym or personal name from the type-locality area of Rondônia.
Morphology
Adult males of Moema pepotei reach approximately 1.5–2 in standard length, with the holotype male measuring 2 in SL. This places the species at a mid-range size for the genus — stockier and larger than many dwarf annual killifishes but modest in comparison with the largest Austrolebias or Pterolebias. Females in the annual killifish lineage are typically smaller and more cryptically coloured than males, a pattern consistent across rivulid annuals, though detailed morphometric data for female pepotei are sparse in the available sources.
As with other Moema species, the body shape is moderately deep and laterally compressed, with the dorsal and anal fins set relatively far back on the body — a typical annual killifish silhouette adapted to bottom-orientated spawning behaviour. Males display the vivid patterning characteristic of Moema: iridescent lateral flanks with pigment patterns used in intraspecific signalling. Detailed fin-ray counts and scale formulae are given in the original Costa (1993) description but are not reproduced here from secondary sources.
Habitat
Moema pepotei is native to the upper Río Madeira system, specifically the Guaporé/Iténez sub-basin that forms the border between Rondônia state in south-western Brazil and the Beni department of north-eastern Bolivia. The IUCN 2020 assessment records the species from both Bolivia and Brazil. The río Guaporé and its associated floodplain is a major tributary system of the upper Madeira, draining seasonally inundated savannas and gallery forests in the transition zone between Amazonian forest and the Cerrado/Pantanal ecotones.
Like all Moema species, M. pepotei inhabits temporary pools and ephemeral wetlands that fill during the Amazonian rainy season and dry out completely for weeks to months each year. These pools typically accumulate soft, organic-rich substrate — decomposed leaf litter, peat, fine clay — and carry the slightly acidic, low-conductivity water characteristic of many Amazonian seasonal habitats. Based on conditions typical of the Guaporé floodplain and in line with congener data, pH of approximately 6.4–6.6 and warm temperatures (75–82 °F) are likely; the pools may be tea-coloured with tannins from decaying vegetation.
The temporary nature of these habitats is both the ecological driver of the annual life cycle and the primary threat to the species: pools that drain predictably each dry season are also vulnerable to permanent loss through land conversion, water diversion, or changes in the hydrological cycle driven by deforestation in the catchment.
Feeding
Moema pepotei, like other South American annual killifishes, is a micro-predator and opportunistic carnivore in the wild. The shallow, temporary pools it inhabits are rich in small invertebrates — aquatic insect larvae, microcrustaceans, small worms, and zooplankton — and these form the bulk of the wild diet. Annuals must grow fast and reach reproductive maturity within a single wet season, so high-protein prey is energetically prioritised.
In the aquarium, M. pepotei readily accepts live and frozen invertebrate foods: Daphnia, Artemia nauplii and adults, bloodworm (Chironomus larvae), Tubifex, and small earthworms are all suitable and encourage good condition and colouration in males. Dry foods such as small pellets and granules formulated for killifishes can be offered as a supplement but should not be the sole diet. Feeding small amounts frequently — two to three times daily — mimics the opportunistic foraging pattern of wild annual killies and helps maintain the rapid growth rate these fish are capable of.
Mating
Moema pepotei is an annual peat-spawner with a substrate-diving reproductive strategy characteristic of all South American annual killifishes. When a male courts a female, courtship involves lateral displays in which the male presents his flank — showing the full extent of his iridescent colour pattern — and erects his fins. If the female is receptive, the pair move together and press side by side, with the male wrapping around or aligning tightly with the female in the classic killifish spawning clinch.
At the moment of spawning, the pair dive together into soft substrate — in nature, the silty organic mud or detritus of the pool floor; in captivity, a layer of peat or coir — and a single egg (or a small number of eggs) is deposited and fertilised within or just below the surface of the medium. The pair immediately back out and may repeat the dive multiple times across a spawning session. This substrate-diving act is the defining feature of the annual killi mating system, and it is the mechanism by which the diapausing eggs are buried safely for the dry season.
Breeding
The eggs of Moema pepotei, buried in substrate, enter diapause — arrested embryonic development — that allows them to survive the complete desiccation of the pool during the dry season. FishBase records an incubation period of approximately six months for M. pepotei under peat-storage conditions, consistent with the length of the dry season in the Guaporé basin. During this storage period the peat is kept only slightly moist at a stable warm temperature; hatching is triggered by re-wetting the medium with soft, warm water, which simulates the return of seasonal rains.
In the hobbyist approach — which closely mimics the natural cycle — the spawning medium (peat or coir) is collected from the aquarium every four to six weeks, gently squeezed to remove excess water, sealed in a plastic bag, labelled with the collection date, and stored at 75–79 °F in a warm, dark place for the appropriate incubation period. After roughly six months, the peat is placed in a shallow tray and covered with soft, slightly acidic water at around 75 °F; fry appear within hours to a day or two of re-wetting.
Fry are relatively robust at hatching compared with some annual killi species. They can be started on freshly hatched Artemia nauplii immediately; infusoria is usually not required. Growth is rapid — annual killies must be sexually mature within a single wet season — and juveniles can be sexed within a few weeks. Males should be separated as they mature to reduce fighting. The total aquarium lifespan of M. pepotei, even under ideal conditions, is likely to be well under two years, reflecting the short-lived nature of all true annual killifishes.
In the aquarium
Moema pepotei is a specialist fish suited to experienced killifish keepers familiar with the peat-spawning annual technique. A small, species-only aquarium of 10–15 US gal is adequate for a pair or a trio (one male, two females); multiple males will fight persistently. The tank should have a tight-fitting lid, subdued lighting, and a layer of floating plants or surface cover to reduce stress. A dark substrate and background encourage the male to display his full colour pattern.
Water chemistry should target the soft, slightly acidic conditions of the Guaporé floodplain: temperature 75–81 °F, pH 6.0–6.8, low hardness. The tank does not need to be large, but water quality must be maintained with regular small water changes — annual killies are sensitive to accumulated nitrates even though they evolved in temporary pools, because those pools are regularly renewed by rain and inflow.
A spawning medium — a layer of peat, coir fibre, or peat/sand mix — should be provided on the tank floor or in a small container to allow the fish to dive-spawn. The medium is collected every three to four weeks, stored as described in the Breeding section, and a fresh layer provided. Keeping a rolling series of stored peat batches at different stages ensures a steady supply of fry. Moema pepotei is not a fish for the general community aquarium, but for the killifish hobbyist it offers the fascination of one of nature's most remarkable life cycles: a fish that literally dies each year and is reborn from buried eggs.
Conservation
The IUCN Red List assessed Moema pepotei as Least Concern in December 2020 (assessment date 2020-12-14), reflecting an estimated range that extends across portions of both Rondônia state in Brazil and north-eastern Bolivia in the Guaporé/Iténez basin. The LC assessment implies that no immediate collapse of the population is anticipated at the species level, but it should not be read as a clean bill of ecological health.
The temporary pool habitats on which M. pepotei and all annual killifishes depend are among the most ecologically vulnerable freshwater habitats in the Amazon periphery. Deforestation in the Cerrado–Amazon transition zone of Rondônia — one of the most heavily deforested biomes in Brazil — reduces the tree cover that moderates pool hydrology, increases sedimentation, and can alter the wet/dry seasonality that drives the annual killi life cycle. Agricultural conversion of seasonally flooded savannas and gallery forest margins to cattle pasture or soy cultivation destroys pool habitat permanently. The río Guaporé basin has experienced significant land-use change pressure over recent decades.
Annual killifishes are also intrinsically fragile to localised habitat loss because many species have small, naturally patchy distributions tied to specific pool systems; if the pools at a locality are destroyed, there is no recolonisation from refugia the way longer-lived fishes might recover from a river. The LC status of M. pepotei is plausible given its occurrence in two countries, but continued monitoring of the Guaporé floodplain and its associated temporary wetlands is warranted to detect any deterioration before population declines become acute.