Taxonomy & naming
Scolichthys greenwayi was described by the American ichthyologist Donn Eric Rosen in 1967 and is the type species of the genus Scolichthys, which Rosen erected for it. The fish belongs to the order Cyprinodontiformes, family Poeciliidae and subfamily Poeciliinae — the New World livebearing toothcarps that include the guppies, mollies, swordtails and their many small Central American relatives. Eschmeyer's Catalog of Fishes treats Scolichthys greenwayi Rosen, 1967 as the valid name.
The genus name combines the Greek skolex, "worm," with ichthys, "fish." The species epithet greenwayi honours Dr James Cowan Greenway Jr. (1903–1989), an American naturalist and collector. As a small, geographically restricted poeciliid from a single Guatemalan drainage, the species has never been a fixture of the aquarium hobby, and most of what is recorded about it derives from collection material and the livebearer reference literature rather than from a large body of field study. Where the cache and reliable knowledge are silent, this article says less rather than guessing.
Morphology
Scolichthys greenwayi is a small fish. Published figures give males and unsexed individuals to about 1.5 in total length, with females reaching roughly 2 in — the larger-female, smaller-male pattern typical of poeciliids. The body is the compact, somewhat elongate form usual for a stream-dwelling livebearer of this size.
As in all poeciliids, the sexes differ in the structure of the anal fin: mature males carry a gonopodium, an intromittent organ formed from modified anal-fin rays and used to transfer sperm to the female, while females retain a normal fan-shaped anal fin. Detailed colour and meristic descriptions for this species are sparse in the accessible literature, so this account does not assert pigment patterns or fin counts that cannot be traced to a reliable source.
Habitat
The species is endemic to Guatemala, where it is recorded from the Río Chixoy and Río Salinas system in Alta Verapaz, in the country's central highlands. This is upland limestone country, and the fish inhabits flowing fresh waters rather than still pools, described as a pelagic freshwater species of running streams.
Water conditions reported for the species are neutral to alkaline and hard — pH on the order of 7.0 to 8.0, hardness of about 10 dH or more, and tropical temperatures of roughly 68–75 °F. These figures are consistent with a hard-water, calcareous drainage. Because the species is known from a single restricted river system, its entire global range is small, a fact directly relevant to its conservation profile.
Feeding
Detailed dietary studies of Scolichthys greenwayi are not available in the accessible literature, and the species carries an estimated trophic level of about 3.0 — the intermediate value typical of a small omnivorous to micro-predatory stream fish. On that basis it is best understood as a generalist that takes a mix of small invertebrates, insect larvae, and algal and detrital material from flowing water, in the manner of comparable small Central American poeciliids.
No specific aquarium feeding regime is documented for this rarely kept species. By analogy with other small livebearing toothcarps, a varied diet of fine prepared foods together with small live and frozen items would be appropriate, but in the absence of direct husbandry reports this article does not present such guidance as established fact for S. greenwayi specifically.
Mating
Reproduction in Scolichthys greenwayi is internal, as in all poeciliids. The male uses the gonopodium — the rod-like intromittent organ formed from modified anal-fin rays — to transfer sperm directly to the female, so fertilisation occurs inside the female's body rather than in open water. This is the defining reproductive feature of the New World livebearers and distinguishes them sharply from the egg-laying killifishes to which they are sometimes superficially compared.
The specific courtship behaviour of this species has not been documented in the accessible literature. In poeciliids generally, males pursue females and may both court and attempt sneak inseminations, and females of many species can store sperm internally to fuel successive broods from a single mating; whether and to what degree these behaviours, including superfetation, occur in S. greenwayi is not established here and is therefore not asserted as fact.
Breeding
Scolichthys greenwayi is viviparous: after internal fertilisation the female carries the developing embryos and gives birth to free-swimming young rather than laying eggs. Reported figures give a gestation of about 28 days, after which the female produces a brood of roughly 10 to 30 young. The species is rated as having high reproductive resilience, with a minimum population doubling time of under 15 months — consistent with the fast, prolific breeding seen across small poeciliids.
The newborn fry of livebearing toothcarps are fully formed miniature fish, able to swim and feed from birth. Beyond the gestation period and brood size noted above, detailed breeding observations specific to this species are sparse, and this article does not extrapolate fry-rearing detail that cannot be traced to a source.
In the aquarium
Scolichthys greenwayi is not a fish of the general aquarium trade; it is known chiefly from collections and specialist livebearer literature rather than from broad commercial availability. As such, there is no large body of established husbandry practice for it, and any keeping would be the province of dedicated livebearer specialists rather than the general hobby.
What can reasonably be inferred from its native waters is that it would require flowing, well-oxygenated, hard and neutral-to-alkaline conditions at tropical temperatures of roughly 68–75 °F — matching the calcareous upland streams it comes from. Because firm, species-specific captive-care reports are not available, this section deliberately stops short of presenting a detailed care recipe as proven for S. greenwayi.
Conservation
Scolichthys greenwayi is assessed as Data Deficient (DD) on the IUCN Red List, an assessment dated 16 October 2019 under the IUCN 3.1 criteria. The Data Deficient category means there is not enough information on the species' distribution, population status or threats to make a confident assessment of its extinction risk — it is a statement of uncertainty, not of safety.
That uncertainty matters because the species is endemic to a single, restricted river system — the Río Chixoy and Río Salinas drainage of Alta Verapaz, Guatemala. Narrowly endemic freshwater fishes of this kind are inherently vulnerable to localised pressures such as habitat alteration, water extraction and pollution within their small range, even where formal data are lacking. For an endemic Data Deficient species, the responsible reading is that targeted survey work is needed before its true status can be known.