Taxonomy & naming
Plesiolebias altamira was described by Wilson J. E. M. Costa and J. Nielsen in Costa (2007), with the type locality given as temporary pools near the city of Altamira, state of Pará, Brazil — pools associated with the Rio Xingu drainage, a major southern tributary of the Amazon. The Catalog of Fishes (Eschmeyer, Fricke & van der Laan) treats Costa & Nielsen in Costa, 2007 as the valid authority. The specific epithet altamira is a toponym, directly referencing the city near which the type series was collected by J. Diniz on 5 May 2003.
The genus Plesiolebias belongs to the family Rivulidae (South American annual killifishes) and was erected to accommodate a cluster of small, seasonally restricted annuals from central Brazil and surrounding lowlands. Rivulidae as a whole contains dozens of genera spanning the Neotropics from Trinidad and the Guianas south to the Río de la Plata basin; Plesiolebias sits within the annual-killi radiation that independently evolved the diapause-egg strategy in multiple South American lineages. FishBase records dorsal-fin rays 10–12, anal-fin rays 14–16, and vertebrae 25–27 for this species, counts consistent with the genus.
Morphology
Plesiolebias altamira is a diminutive fish: FishBase gives a maximum standard length of 0.5 in (0.5 in SL), with a total length of approximately 1 in reported from the hobbyist literature. Males are more intensely coloured, as is typical across the rivulid annuals, bearing the species' patterning against a background body colour; females display scattered spots that form oblique bars along the sides, a useful field mark distinguishing them from males at a glance.
The body plan is that of a typical bottom-oriented annual killi: laterally compressed, with a relatively dorsal placement of the eyes and an upturned mouth adapted to surface-zone and near-substrate feeding. The species is classified as benthopelagic by FishBase. Like all Plesiolebias, the fins are rounded and the overall silhouette is compact — the anatomy of a fish that must complete its entire adult life in a few weeks or months before its pool evaporates.
Habitat
This species inhabits temporary seasonal pools within the Rio Xingu drainage, state of Pará, in the Brazilian Amazon. These pools form during the wet season when rains flood low-lying terrain, and they dry out completely during the dry season — leaving no permanent water connection. The pools are shallow, often vegetated or lined with soft organic substrates (peat, mud, leaf litter, and detritus) that accumulate and hold the buried eggs through the dry months.
Water chemistry data from a comparable Xingu-region habitat (from academic literature on the area, including a study describing a co-occurring rivulid from state Pará) indicates dark, acidic water: pH around 5.5, temperature approximately 80 °F at shallow depths. The Xingu is known for its clear, mineral-poor, tea-coloured waters where they pass over the Guiana and Brazilian shields, and the lateral pools it floods during high water reflect those characteristics — soft, warm, and acidic. The fish does not occur in permanent river channels but strictly in the ephemeral pool habitats that define the annual-killi lifestyle.
Feeding
Like other small rivulid annuals, Plesiolebias altamira is a micro-predator in the wild, subsisting on the zooplankton, aquatic insect larvae, and other small invertebrates that colonise temporary pools rapidly after flooding. The species' upturned mouth and benthopelagic orientation suggest feeding both at the water surface and through the water column in the shallow pools it inhabits.
In captivity, fry are initially fed on infusoria or equivalently fine microfoods — the mouth at hatching is tiny even by killifish standards. After one to two weeks, newly hatched Artemia nauplii become suitable. Adults can be maintained on live and frozen Artemia, micro-worms, and other small invertebrate foods. The species is delicate and stress-prone, so a calm feeding environment without competition from larger tankmates is important to ensure individuals feed consistently.
Mating
Plesiolebias altamira is an annual killifish and practises the substrate-spawning, diapausing-egg reproductive mode that defines this life-history guild. Pairs court in the water column above soft substrate; the male pursues and displays to the female, and upon acceptance the pair align side-by-side and dive together into the muddy or peaty bottom. Eggs are deposited directly into the substrate with each spawning embrace, buried where the eggs will remain protected during the dry season.
Males of Plesiolebias and related genera tend to dominate spawning; the hobbyist literature for this species notes that males often make up more than 90 percent of fry from a batch, a sex-ratio skew documented in some annual rivulid species and thought to reflect genetic or developmental factors. In the aquarium, multiple spawning dives occur over several weeks before the female is exhausted or the keeper collects the medium.
Breeding
Breeding in captivity follows the standard annual-killi protocol. The spawning pair is placed over a container of soft peat or coir fibre that is deep enough for the fish to dive into comfortably. After three to four weeks of spawning, the medium is removed, gently squeezed to remove excess moisture, and stored in a sealed bag or container at room temperature (around 75–79 °F) for the diapause period. The embryos undergo arrested development (diapause) within the buried eggs, remaining viable through the simulated dry season.
Incubation for Plesiolebias altamira requires a long diapause of six to nine months, according to observations in the killifish-keeping literature — a duration reflecting the length of the dry season in the Xingu region. After this period the medium is re-wetted with soft, slightly acidic water, and fry hatch within 24–48 hours. The newly hatched fish are small and require fine first foods (infusoria) before graduating to Artemia nauplii after one to two weeks. Maturity is reached in approximately two months — a rapid development consistent with the species' compressed annual life cycle. Wild fish likely live well under a year in total.
In the aquarium
Plesiolebias altamira is a rare and demanding species suited to experienced killifish keepers rather than general community aquarists. It is small, delicate, and stress-prone; the hobbyist literature specifically flags its sensitivity, and it should be maintained in quiet, dedicated species aquaria without competition or harassment from other fish. A small tank (2.5–5.5 US gal) with a dark substrate, minimal decor, and gentle filtration is appropriate; heavy planting or a bare-bottom setup with a peat tray for spawning are both used by specialists.
Water conditions should replicate the soft, warm, acidic chemistry of its Xingu pool habitat: temperature around 79–81 °F, pH in the range 5.5–6.5, very soft water (low conductivity). Avoid hard or alkaline conditions. Feeding must be attentive — offer live or frozen micro-invertebrates rather than dried prepared foods, and ensure all fish are eating. The skewed sex ratio (males dominant in fry batches) means keepers may struggle to maintain females for ongoing breeding; sourcing additional females from other keepers is sometimes necessary. This species is a specialist's fish and a conservation-relevant one — maintaining viable captive colonies supports knowledge of its biology outside the contracting wild range.
Conservation
The IUCN Red List assesses Plesiolebias altamira as Least Concern (LC), with the assessment completed 18 May 2022. However, Least Concern for an annual killifish confined to temporary pools near a single city does not mean the species is without vulnerability. Plesiolebias altamira is a point-endemic of the Altamira region of Pará, and its entire known range falls within an area that has experienced substantial deforestation and agricultural development as part of the broader clearing of the Brazilian Amazon. Seasonal pools of the kind this species requires are easily drained, filled, or degraded by changes in land use — deforestation alters rainfall retention and microhabitat conditions; cattle and mechanised agriculture compact soils and eliminate the soft organic substrates the fish needs for egg burial.
The Xingu basin has also been the site of major hydroelectric development, most notably the Belo Monte dam complex, which has altered hydrology and aquatic habitats across a large area of the middle Xingu. While P. altamira's temporary upland pools may sit outside the directly inundated and dewatered zones, cumulative regional hydrological changes add pressure. As with many highly localised annual killies, the species' survival depends on the persistence of its precise pool microhabitats, and continued deforestation around Altamira represents the primary ongoing threat.