Taxonomy & naming
Moema staecki was described by Lothar Seegers in 1987, with its type locality in the Amazon River basin of Brazil. Eschmeyer's Catalog of Fishes (Fricke, Eschmeyer & Fong) recognises the valid combination as Moema staecki (Seegers, 1987), placed in the genus Moema within the family Rivulidae — the South American annual killifish. The authority is presented in parentheses, indicating that nomenclatural movement has occurred since the original description.
Moema staecki is the nominal type species of the Moema staecki species group, a clade within the genus that includes closely related forms such as Moema humaita. The genus Moema itself belongs to a broader assemblage of Neotropical annual killifish whose members occupy ephemeral seasonal pools across the lowland Amazon basin and its tributaries.
Morphology
Moema staecki reaches a maximum recorded total length of 4.5 in (FishBase), making it a moderately large annual killifish. As in other rivulids, the body is elongate and laterally compressed, built for life in shallow, vegetated pools.
Sexual dichromatism is pronounced, as is characteristic of the genus. Males display vivid iridescent patterning on the flanks and unpaired fins — the intense coloration typical of annual killifish that must attract mates within a compressed breeding season. Females are cryptically coloured with a more subdued, brownish appearance and a rounded belly when gravid. Detailed colour descriptions for this species remain sparse in the accessible literature, but the general Moema body plan — a deep-bodied, colourful male and a plainer female — applies here.
Habitat
Moema staecki inhabits seasonal, ephemeral pools in the Amazon River basin of Brazil. These pools arise with the onset of the annual rains, often forming in low-lying savanna or gallery-forest margins where water accumulates in shallow depressions over impermeable lateritic soils. As the dry season progresses the pools shrink and eventually disappear entirely, leaving only buried eggs in the substrate to carry the population forward.
Water chemistry in these environments is typically soft and slightly acidic to neutral, reflecting the mineralogy of Amazonian lowland substrates. FishBase records a pH of 7.2 and temperatures of 75–82 °F as representative conditions for the species. The pools are characteristically shallow, low in dissolved oxygen, and rich in detritus and leaf litter — conditions that adult annual killifish are adapted to exploit.
Because the species is restricted to ephemeral pool habitat within a limited area of the Amazon basin, it is sensitive to any land-use change that alters the hydrology of those seasonal wetlands.
Feeding
Like other Moema, M. staecki is a benthopelagic opportunist feeding in the water column and near the substrate. The diet in the wild likely consists primarily of small aquatic invertebrates — microcrustaceans, insect larvae, and worms — supplemented by whatever organisms are locally abundant in the transient pool.
In captivity the species accepts a range of live and frozen foods appropriate to its size: bloodworm, Daphnia, Artemia, Tubifex, and similar items. The compressed lifespan of an annual killifish means that regular, nutritious feeding directly influences breeding readiness and condition, and aquarists typically maintain adults on a varied diet of live and frozen invertebrates.
Mating
Moema staecki is a substrate-spawning annual killifish. Pair formation and courtship occur within the transient pool, where males display intensely to females using their vivid flank and fin coloration. The breeding season is tightly constrained by the wet-season calendar, and the urgency of reproduction before the pool dries out drives males to court actively and persistently.
Copulation involves a spawning dive in which the male and female press their bodies together at the substrate surface and push into the soft bottom sediment — peat, mud, or detritus — where a small clutch of eggs is deposited and fertilised. Each dive produces a small number of eggs rather than a large batch, and pairs spawn repeatedly across the available season, incrementally burying eggs at various depths in the substrate.
Breeding
The eggs of Moema staecki are encased in a tough, drought-resistant chorion and enter embryonic diapause once buried — a developmental arrest that allows them to survive the complete desiccation of the pool through the dry season. Wild incubation periods in annual rivulids of this group can span several months, with FishBase recording approximately six months for M. staecki. The eggs progress through one or more diapause phases before completing development and hatching when the rains return and refill the pool.
In the aquarium, annual killifish are bred on a peat or coir substrate into which the pair spawns repeatedly over several weeks. The substrate is then removed, gently squeezed dry (not bone-dry), stored in a sealed bag at room temperature, and kept for the appropriate incubation period — typically three to six months for a species of this group. At the end of this period the peat is re-wetted with cool, soft water, and fry hatch within hours to days. Newly hatched fry are large enough to take small live foods such as freshly hatched Artemia nauplii and microworm from the outset. Growth is rapid in warm water, and the fish can reach sexual maturity in a matter of weeks under good conditions.
In the aquarium
Moema staecki is described by FishBase as difficult to maintain, reflecting the specialist requirements of annual killifish rather than any unusual fragility. The species requires soft, slightly acidic to neutral water (pH around 7, temperature 75–82 °F), a dark substrate, and a well-planted or peat-filtered environment that approximates the dim, tannin-stained conditions of its native pools.
A small, species-specific tank is the recommended approach: a group of one to two males with several females in a tank of 15–20 US gal, heavily planted or furnished with floating vegetation to diffuse light and provide refuge. Aggressive male–male interactions are common and extra females help distribute the males' attention. The short lifespan — most adults in the wild live less than a year — means the aquarist must be prepared to manage the full breeding cycle, including the peat-storage phase, or accept the loss of the colony at season's end. For this reason M. staecki is a fish for committed killifish specialists rather than the general community aquarist.
Conservation
Moema staecki is assessed as Least Concern on the IUCN Red List (2018 assessment). The species' occurrence across part of the Amazon basin of Brazil gives it a broader distribution than many single-locality annual killifish, supporting the LC classification.
Nevertheless, the ephemeral pool habitats that annual killifish depend on are inherently vulnerable. Agricultural expansion, pasture conversion, and drainage of seasonal wetlands in the Amazon basin can eliminate entire local populations of pool-dependent species without leaving any visible trace. Unlike perennial stream fishes, annual killifish have no refuge during the dry season other than the buried egg bank — the destruction of a pool's substrate through ploughing or compaction can extirpate a population instantly. The longer-term conservation picture for M. staecki, as for many Amazonian seasonal-wetland endemics, depends on the fate of the broader lowland Brazilian floodplain environment.