Taxonomy & naming
Girardinus uninotatus was described by Felipe Poey in 1860, the Cuban naturalist whose work laid the foundation for the study of the island's fish fauna. The species sits in the genus Girardinus, the Cuban topminnows, within the family Poeciliidae and the subfamily Poeciliinae — the New World livebearers that include guppies, mollies and mosquitofishes. Eschmeyer's Catalog of Fishes governs the valid name, and FishBase records the species under Cyprinodontiformes > Poeciliidae > Poeciliinae.
The genus name Girardinus honours Charles Frédéric Girard (1822–1895), the French-American herpetologist and ichthyologist who worked as an assistant to Louis Agassiz. The species epithet uninotatus combines the Latin uni- (one, single) with notatus (marked, spotted), giving "single-spotted" — the source of the English name singlespot topminnow.
The species has carried other names in the aquarium hobby. It has circulated under the older name Glaridichthys torralbasi, a synonym associated with it by livebearer keepers; this is a hobby usage rather than a current valid combination, and the Catalog of Fishes name remains authoritative.
Morphology
Girardinus uninotatus is a small fish with marked sexual size dimorphism. FishBase records a maximum of about 2 in standard length for males and a much larger 3.5 in standard length for females, so the sexes differ substantially in size, with females considerably the larger and deeper-bodied of the two. This female-larger pattern is typical of the poeciliid livebearers, where the female must accommodate a developing brood.
As in all the topminnows, the body is elongate and the mouth is set high and angled upward — an adaptation to feeding at and just below the surface, the "topminnow" habit. The colouration is restrained rather than ornamental; the common name singlespot points to a marking on the flank rather than to the scattered, saturated colour spots of a guppy.
The defining male feature is the gonopodium, a slender intromittent organ formed from modified rays of the anal fin. The presence of this structure in the smaller-bodied male, against the larger plain female, is the most reliable way to sex the species and is the visible signature of internal fertilisation in the Poeciliidae.
Habitat
Girardinus uninotatus is endemic to Cuba, where it is a freshwater, demersal, non-migratory fish of tropical streams. FishBase reports it from streams where it prefers pools and the areas along the banks, occasionally venturing into swifter water. This is a fish of marginal, sheltered water rather than open current — the calm pockets along a streambank where a small surface-feeder can hold station and graze.
The species is tropical and warm-water, with a recorded range of roughly 75–82 °F. Its endemism to a single island, combined with a preference for the quieter parts of stream systems, makes it part of Cuba's distinctive and geographically restricted freshwater fish fauna.
Detailed habitat chemistry for this species is data sparse in the cached sources beyond the temperature range; the broader genus tolerates the hard, mineral-rich waters typical of Cuban freshwaters, and aquarium keepers report that warmer temperatures suit it best.
Feeding
In the wild Girardinus uninotatus is a grazing omnivore. FishBase records a diet of diatoms, algae, the leaves of plants, detritus and insect larvae, and places the species at a low trophic level of about 2.2 — squarely that of a herbivore-leaning omnivore that takes a good deal of plant and algal material along with small animal prey. This matches the topminnow body plan, with its upturned mouth suited to picking at surfaces and the surface film.
Hobby accounts of the genus add a more carnivorous emphasis in captivity, describing the Cuban topminnows as taking animal foods readily while still accepting fruit and vegetable matter. The two pictures are complementary: a fish that grazes algae and detritus in the stream but will eat small invertebrate foods enthusiastically when offered.
In the aquarium this translates to an easy feeder. A varied diet of good flake or micro-pellet with a vegetable or algal component, supplemented by small live and frozen foods such as Daphnia or brine shrimp, keeps the fish in good condition and breeding readily.
Mating
Reproduction in Girardinus uninotatus is internal, as in all poeciliid livebearers. The male transfers sperm to the female using the gonopodium, the modified anal-fin organ; fertilisation takes place inside the female, and she carries the developing young internally rather than laying eggs. There is no nest, no spawning site, and no egg-laying — the whole reproductive cycle is internal up to the moment of birth.
The genus is reported in the hobby to require a fresh mating for each pregnancy, rather than relying on long-term stored sperm to fuel a string of broods. In practical terms this means the Cuban topminnows do not exhibit the marked superfetation — overlapping broods at different stages of development — seen in some other poeciliids; superfetation should not be assumed for this species, where the cached evidence points the other way.
The strong size difference between the sexes shapes mating behaviour, with the small male pursuing the much larger female. Beyond this general poeciliid pattern, fine detail of courtship in G. uninotatus specifically is data sparse in the cached sources.
Breeding
Girardinus uninotatus is viviparous: the female gives birth to fully formed, free-swimming fry rather than laying eggs. The young are lecithotrophic — nourished by the yolk of the egg through development rather than by a placental connection — which is the standard mode for the Poeciliinae, and no specialised placental provisioning has been reported for this species. The fry emerge as miniature fish able to swim and feed at once.
Hobbyist reports describe the genus as breeding readily in the aquarium, even in modest tanks of around ten gallons, provided temperatures are kept warm — a suggested minimum of about 75 °F is consistent with the species' wild range of 75–82 °F. As with other livebearers, dense planting or floating cover helps newborn fry escape predation by the adults, including their own mother, until they are large enough to be safe.
Precise brood sizes and gestation length for G. uninotatus are data sparse in the cached sources; given the strong size dimorphism, the larger females can be expected to carry the larger broods, as is the rule among poeciliids.
In the aquarium
Girardinus uninotatus is a hardy, undemanding livebearer well suited to the aquarist with an interest in the less-common Poeciliidae. It is a peaceful, warmth-loving fish that does well in a planted tank kept toward the warmer end of the tropical range, broadly 75–82 °F. Hobby guidance for the genus recommends giving the fish room — a tank of at least about 23.5 in in length — which suits an active surface-and-midwater shoaling species and gives the adults and any fry space to spread out.
A varied diet keeps the fish healthy: a good staple food with a vegetable or algal component, supplemented by small live and frozen foods. Warm, clean, stable water and a well-planted layout that offers cover for fry are the main husbandry points; this is not a delicate fish, and it breeds freely under ordinary livebearer conditions.
Girardinus uninotatus is not a brightly coloured "display" fish in the way of fancy guppies, so it appeals most to keepers who value endemic livebearers and the behaviour of a true wild-type species. Sourcing healthy stock from livebearer specialists or associations is the practical route to keeping it, as it is not a common shop fish.
Conservation
Girardinus uninotatus is assessed as Least Concern on the IUCN Red List, in an assessment dated 4 May 2020 (Red List version 2025-2). The species is endemic to Cuba but is evidently sufficiently widespread and secure within the island's stream systems not to qualify for a threatened category at present.
FishBase notes the species is not evaluated under CITES or CMS, is harmless to humans, and carries a low fishing vulnerability; its resilience is rated medium, with an estimated population doubling time of roughly 1.4 to 4.4 years. These are the marks of a small, fast-reproducing fish that can recover quickly from disturbance.
As with any single-island endemic, the species' long-term security rests on the health of Cuba's freshwater habitats — the streams and their bankside pools where it lives. A Least Concern listing reflects current abundance rather than a guarantee, and the usual aquarist caution applies: a non-native island livebearer should never be released into local waters outside its range.