Taxonomy & naming
Gambusia lemaitrei was described by the American ichthyologist Henry Weed Fowler in 1950, on the basis of Colombian material. The species honours Ernesto D. Lemaitre, a Colombian naturalist and angler associated with the collection of the type specimens. Eschmeyer's Catalog of Fishes treats Gambusia lemaitrei Fowler, 1950 as the valid name, placing it in the genus Gambusia within the subfamily Poeciliinae of the family Poeciliidae, the New World livebearers.
Gambusia is a large, predominantly North and Central American genus — its best-known members are the western and eastern mosquitofishes, Gambusia affinis and G. holbrooki, spread around the world for mosquito control. G. lemaitrei is one of only a small number of Gambusia that reach South America, where it is endemic to Colombia. Its position within the genus has not been the subject of detailed modern phylogenetic study, and beyond its place in Lucinda's 2003 checklist of the South and Central American Poeciliidae the species has attracted little taxonomic attention. The genus name Gambusia derives from the Cuban Spanish word gambusino, used in the expression for fishing and catching nothing — a wry reference to how inconsequential these small fishes seemed to early collectors.
Morphology
Gambusia lemaitrei is a small poeciliid. FishBase records a maximum size of about 1 in standard length for males and unsexed fish, after Lucinda (2003), with females reaching roughly 1.5 in — the larger female size being the usual pattern in the genus. As in other Gambusia, the body is compact and somewhat laterally compressed, with the mouth set upturned for surface and mid-water feeding, an arrangement well suited to taking small prey from the upper water column.
The species shows the sexual dimorphism characteristic of the poeciliids. Females are larger and deeper-bodied; males are smaller and bear the gonopodium, a slender intromittent organ formed from modified rays of the anal fin and used to transfer sperm internally. Detailed colour and meristic descriptions specific to G. lemaitrei are sparse in the accessible literature, and the fish is, like most mosquitofishes, plainly coloured rather than ornamented — silvery to olive flanks without the bright spotting of the showier livebearers. Any finer points of pattern should be regarded as poorly documented for this species.
Habitat
Gambusia lemaitrei is endemic to Colombia, in northern South America. FishBase characterises it as a benthopelagic, tropical freshwater and brackish-water fish, recorded from the shallow zones of lakes and reported also from brackish coastal waters — a salinity tolerance shared with many Gambusia and consistent with a fish at home in low-lying, near-coastal environments. Reported water temperatures fall in the warm tropical range of roughly 75–82 °F.
The species is range-restricted, a Colombian endemic associated with the country's northern lowland and coastal drainages. As with other shallow-water mosquitofishes, it would be expected in warm, slow or still waters — lake margins, backwaters, ditches and coastal lagoons — where surface-feeding live-bearers thrive. Precise locality data and habitat detail beyond these broad strokes are limited in the available record, which is part of why the species remains formally Data Deficient; its distribution is better described as "endemic to Colombia" than tied to any well-studied set of sites.
Feeding
No diet study specific to Gambusia lemaitrei is available, and FishBase carries only a modelled trophic level of about 3.2, indicating a small carnivore or micro-predator rather than a herbivore. This is entirely in keeping with the genus: mosquitofishes are opportunistic feeders on small aquatic invertebrates, insect larvae — mosquito larvae prominent among them, the basis of the group's common name — zooplankton, and other small drifting items taken from the surface and upper water column.
The upturned mouth points to surface and near-surface feeding, and a fish of warm shallow waters would take whatever small prey those habitats offer. In the absence of species-specific observations, the responsible summary is that G. lemaitrei is almost certainly a generalist micro-predator and omnivore on the genus model, supplementing animal prey with incidental algae and detritus, but the particulars of its wild diet are undocumented (data sparse).
Mating
Like all poeciliids, Gambusia lemaitrei reproduces by internal fertilisation. The male transfers sperm to the female using the gonopodium, the modified anal fin that is the defining feature of the family; courtship in Gambusia is typically brief and dominated by persistent male pursuit and sneak copulation attempts rather than the elaborate displays seen in some other livebearers. Females are larger than males and, as in the genus generally, can store viable sperm internally, allowing successive broods to be produced from a single mating.
Species-specific mating behaviour for G. lemaitrei has not been described in the accessible literature, so the account here is inferred from the well-known reproductive biology of Gambusia. Mosquitofishes are not known for parental investment beyond gestation, and males do not defend territories or care for young. Unlike some poeciliids — notably certain Heterandria and Poeciliopsis — Gambusia are not reported to practise superfetation, the simultaneous carrying of broods at different developmental stages; their gestation runs as discrete successive broods.
Breeding
Gambusia lemaitrei is a live-bearer. FishBase classifies its reproductive guild as internal live-bearing (ovoviviparous/viviparous), with development lecithotrophic — the embryos nourished chiefly by yolk rather than by a placental connection — and no superfetation documented, the standard Gambusia pattern. After internal fertilisation the female carries the developing young and gives birth to free-swimming fry rather than laying eggs.
No brood-size or gestation figures specific to this species are published in the sources at hand, so the expected values are those of the genus: gestation of roughly three to four weeks at tropical temperatures, with broods ranging from a few fry to a few dozen depending on the female's size and condition. The newborn fry are fully formed miniature fish, able to swim and feed immediately, and — as is typical of mosquitofishes — receive no parental care and may be cannibalised by adults. The species' modelled resilience is high, with an estimated population-doubling time of under fifteen months, reflecting the fast, prolific live-bearing strategy of the group; the precise breeding particulars for G. lemaitrei itself, however, remain undocumented.
In the aquarium
Gambusia lemaitrei is effectively absent from the aquarium hobby. No dedicated care page for the species could be located through specialist livebearer resources, and it is best understood as a rarely kept, non-commercial Colombian endemic rather than a trade fish. There is, accordingly, no species-specific husbandry literature, and any keeping notes can only be inferred from general Gambusia practice.
On the genus model, mosquitofishes are hardy, undemanding and tolerant of a wide range of conditions, including the warm (roughly 75–82 °F) and slightly brackish water that suits G. lemaitrei in the wild. They are prolific live-bearers that breed readily, so population control becomes the main management task, and they have a reputation for fin-nipping and aggression toward more delicate tankmates — Gambusia are generally poor community fish and are better kept in single-species groups. These remarks are extrapolated from the genus, not from documented experience with this species; aquarists should treat husbandry detail for G. lemaitrei as inferred rather than established (data sparse).
Conservation
Gambusia lemaitrei is assessed as Data Deficient (DD) on the IUCN Red List. The Data Deficient category means there is not enough information on the species' distribution, population size or trend to assign a meaningful threat category — it is neither a clean bill of health nor a determination of threat, but a statement that the species is too poorly known to evaluate.
That status fits a range-restricted Colombian endemic that has attracted little study. As a fish of shallow lake and coastal waters, G. lemaitrei would be exposed to the pressures that act on such habitats — pollution, habitat alteration and the spread of introduced fishes — but in the absence of population data none of this can be quantified for the species. The practical conservation priority for a fish like this is straightforward: better field survey and basic biological documentation, so that a future assessment can rest on evidence rather than on the genus and a handful of museum records.