Taxonomy & naming
Cyprinodon meeki was formally described by the American ichthyologist Robert Rush Miller in 1976, with the original account published in the Bulletin of the Southern California Academy of Sciences (volume 75, number 2). The type series spanned 0.5–2.5 in, collected from spring-fed localities in the state of Durango, Mexico. Eschmeyer's Catalog of Fishes (Fricke, Eschmeyer & Fong) recognises Cyprinodon meeki Miller, 1976 as the valid name, with the authority unparenthesised because Miller himself erected the genus combination.
The species belongs to the family Cyprinodontidae and the large, widespread genus Cyprinodon — the pupfishes — which is the defining lineage of the North American desert-spring killifish radiation. The genus name derives from the Greek kyprinon (carp) and odon (tooth), referring to the distinctive tricuspid, incisor-like teeth that Cyprinodon species use to scrape algae and organic films from hard substrates. The specific epithet honours Seth Eugene Meek (1859–1914), the Illinois-born ichthyologist who spent much of his career at the Field Museum of Natural History in Chicago and made foundational contributions to the knowledge of Mexican freshwater fishes.
Within Cyprinodon, meeki is placed among the Mexican highland species of the genus. The American Killifish Association classifies it as a Class 1 New World Non-Annual, consistent with its life in stable spring systems rather than ephemeral seasonal pools. The dorsal fin typically carries 10–12 rays (usually 10), a meristic detail recorded in Miller's original description.
Morphology
The Catarina pupfish is a compact, deep-bodied fish typical of the genus Cyprinodon: laterally compressed, with a short snout, large eyes, and an upturned mouth bearing the tricuspid teeth characteristic of the pupfish clan. FishBase records a maximum total length of 2 in TL, with a more typical adult size around 1.5 in TL — placing it among the smaller members of its genus. The body form reflects the shallow-water, benthic-to-midwater lifestyle of a fish that spends much of its time browsing hard surfaces in bright, clear spring outflows.
Colouration in males is strongly sexually dimorphic, particularly during breeding condition. Males develop vivid iridescent blue or blue-green flanks with darker vertical banding and a yellowish to orange wash on the fins — the intense coloration typical of isolated spring pupfishes, where sexual selection in small, closed populations has driven striking male ornamentation. Females are more plainly coloured, showing brownish to olivaceous flanks with less distinct banding and no blue iridescence. Outside of breeding condition, males are less vivid but still show traces of lateral iridescence distinguishing them from females.
Habitat
The Catarina pupfish is endemic to spring-fed watercourses in Durango state, north-central Mexico, in the foothills and plateaux of the Sierra Madre Occidental. Collection localities documented by the American Killifish Association include Veintisiete de Noviembre, Río Canatlan, Ojo Garabato, Morcillo, and Labor — a cluster of spring heads and associated outflow streams that together form an extremely restricted range. These habitats are characteristic of the Mexican highland spring systems: clear, hard, alkaline water with stable temperatures maintained by groundwater discharge, often surrounded by dry, semi-arid scrub vegetation.
As a Cyprinodon, the species is adapted to water chemistry that many freshwater fish would find marginal: high mineral content, alkaline to mildly basic pH, and temperatures that can fluctuate with the seasons more than in the lowland tropics but remain within the tolerances of a small, metabolically active fish. The shallow, sunlit spring margins where the species lives support dense algal and diatom growth — the biofilm that forms the base of the pupfish's diet. Permanent spring outflows provide stability against the seasonal drought that makes Mexican highland streams episodic in many areas, but this permanence also makes the species critically dependent on the continued flow of a small number of springs.
Feeding
Like other members of the genus Cyprinodon, the Catarina pupfish is principally an aufwuchs grazer and opportunistic omnivore. The characteristic tricuspid teeth allow it to rasp diatoms, algae, organic detritus, and bacterial biofilm from rock surfaces, submerged plant stems, and sediment. This grazing mode is supplemented by picking up small invertebrates, crustacean fragments, and any other small organic particles encountered during foraging — a flexible feeding strategy well suited to the productive but often resource-limited spring environments it inhabits.
In the aquarium the species accepts a broad range of small prepared foods readily. High-quality flake, micro-pellets, and frozen foods such as daphnia, cyclops, and artemia nauplii are all suitable; a vegetable component — spirulina-enriched foods or blanched greens — is valuable given the algivorous element of the wild diet. Feeding frequency and variety support the bright condition and active behaviour that make this species interesting to maintain.
Mating
The Catarina pupfish is a non-annual killifish and breeds in the manner typical of Cyprinodon and other spring-dwelling toothcarps: continuous or near-continuous spawning throughout the warmer months, with pairs or small groups depositing adhesive eggs on submerged plant stems, fine-leaved vegetation, algal mats, spawning mops, or other suitable fine structure at or near the substrate. There is no single defined breeding season tied to a dry-wet cycle, and no diapause; eggs develop directly in water without burying into sediment.
Males in breeding colour actively court females with lateral displays and quivering, showing off the vivid blue flanking and fin coloration. Courtship in Cyprinodon is often vigorous and can be persistent to the point of harassment; males may pursue females relentlessly, and in small aquaria with unequal sex ratios this can lead to physical stress in females. A male will court multiple females opportunistically. Spawning involves a brief side-by-side embrace near the chosen substrate, during which a small number of eggs are deposited and fertilised. The pair separates and resumes activity immediately, with further spawning bouts occurring throughout the day.
Breeding
Eggs of the Catarina pupfish are small, adhesive, and transparent to slightly amber-tinted, attached individually or in small clusters to fine vegetation, spawning mops, or algal substrate. Incubation occurs directly in water — this is not a peat-burying species, and no diapause takes place. In warm water (around 75–79 °F) eggs hatch in approximately 10–14 days, producing fry that are small but robust and begin feeding within a day or two of hatching. The absence of parental care means adults will consume eggs and fry opportunistically, so breeding groups are best managed in densely planted tanks or with spawning mops removed daily for separate incubation.
The continuous breeding cycle and relatively rapid development mean that a well-managed group can produce fry throughout the warm season. Fry are best started on infusoria or commercial fry foods, graduating to baby brine shrimp nauplii and finely powdered flake as they grow. The American Killifish Association has documented this species in hobbyist culture across multiple decades (8 JAKA articles from 1966 to 2024), and collection data from multiple Durango localities suggests some genetic variation among populations that serious breeders track by locality code.
In the aquarium
The Catarina pupfish is a manageable and rewarding species for the specialist killifish hobbyist, kept in small, well-filtered aquaria of 10–20 US gal. Hard, alkaline water replicating the spring chemistry of its native Durango habitats is ideal: a pH in the range of 7.5–8.5 and moderate to high mineral content suit the species well. Temperature in the range of 68–79 °F covers the typical conditions of Mexican highland springs; the species tolerates somewhat cooler temperatures during winter but thrives best with a warm-season peak. Bright lighting encourages algal growth on décor surfaces, providing both natural foraging and the visual backdrop against which male colour shows best.
The aggressive courtship behaviour of males means that a group is best kept with a higher female-to-male ratio (two or three females per male) and sufficient surface area and visual breaks — fine-leaved plants, spawning mops, and rock arrangements — to allow females to escape persistent males. The species should not be mixed with other Cyprinodon where hybridisation is a risk; the AKA recommends careful strain management and locality tracking to preserve the genetic integrity of captive populations, particularly given the species' threatened status in the wild. This is a fish that benefits from its hobbyist community: captive breeding by AKA members represents a meaningful ex-situ complement to what remains of the wild population.
Conservation
The IUCN Red List assesses Cyprinodon meeki as Endangered under criteria B1ab(i,ii,iii)+2ab(i,ii,iii) in an assessment by Lyons and Contreras MacBeath, published in 2019 (assessment version 2025-2). The B-criterion application reflects both the extremely small extent of occurrence and area of occupancy, and the continuing decline in each — primarily through the degradation and loss of the spring habitats on which the species depends.
The principal threats are those common to Mexican highland spring endemics: groundwater extraction for agriculture and human consumption, which reduces or eliminates spring discharge; habitat modification around spring heads through livestock access, channelisation, and diversion; and the introduction of non-native fishes — particularly mosquitofish (Gambusia spp.) and other Cyprinodon — which compete with, predate upon, and hybridise with native spring endemics. The Durango spring system is not a protected area in any formal sense, and enforcement of water-use regulations in this part of Mexico is limited.
The role of the killifish hobbyist community is consequential for this species. The American Killifish Association has maintained captive populations and published care and breeding information across eight decades of engagement with this species; these captive populations, managed by locality code, form a practical ex-situ reserve. Any recovery or reintroduction programme for the Catarina pupfish will depend on the continued existence of well-documented captive lines — making responsible hobbyist record-keeping a direct conservation contribution.