Taxonomy & naming
Zoogoneticus purhepechus was described in 2008 by Omar Domínguez-Domínguez, Rodolfo Pérez-Rodríguez and Ignacio Doadrio, in a paper in Revista Mexicana de Biodiversidad (79: 373–383) that combined morphological and genetic comparison of populations previously lumped under Zoogoneticus quitzeoensis. The authors found that fish from the western part of the range formed a distinct lineage and named them as a new species. The holotype is a mature male of 1.5 in SL (CPUM-1509), collected in November 2002 from La Luz spring — also known as Presa Verduzco — in the Río Duero drainage of the lower Río Lerma system, near Zamora de Hidalgo, Michoacán. Eschmeyer's Catalog of Fishes treats Zoogoneticus purhepechus Domínguez-Domínguez, Pérez-Rodríguez & Doadrio, 2008 as the valid name.
The genus name Zoogoneticus derives from Greek zoon (a little animal) and a Latin/Greek element for generation or birth — a reference to the live-bearing habit of these goodeids. The specific epithet purhepechus honours the Purhépecha (Tarascan) indigenous people of the type-locality region in Michoacán, which is also the source of the English common name Tarascan splitfin. The species is also called the La Luz splitfin after its type spring, and Picote La Luz in Mexican usage.
The species belongs to the family Goodeidae, subfamily Goodeinae — the viviparous goodeids endemic to the Mesa Central of Mexico — within the order Cyprinodontiformes. Its sister species is Zoogoneticus quitzeoensis, from which it differs by a shorter preorbital distance, a longer dorsal-fin base and a higher dorsal-fin ray count (13–14 versus 11–13). Mitochondrial cytochrome-b data separate the two by roughly 3–3.8 percent, and within Z. purhepechus three evolutionarily significant units (ESUs) have been recognised, corresponding to the Río Lerma/Lake Chapala basin, the upper Río Ameca and Laguna Magdalena, and the endorheic Atotonilco–Sayula–San Marcos systems.
Morphology
The Tarascan splitfin is a small, compact goodeid. The maximum standard length reported in the original description is 2 in SL, with the holotype a mature male of about 1.5 in SL; FishBase lists a maximum of 1.5 in SL, a figure that sits below the describing authors' own maximum and should be read against it. Length at first maturity is around 1 in. The fish is moderately deep-bodied with 13–14 soft rays in both the dorsal and the anal fins, and a short gut and small, pointed mouth set with conical teeth — the build of a visual micro-predator rather than a grazer.
Both sexes are a light brown, marked with dark-brown spots on the posterior body and the base of the caudal fin, and with a pair of characteristic spots on the caudal peduncle over the hypural plate. Males are slightly darker than females and carry a bluish to greenish iridescent sheen. The most striking feature is colour on the fins: males from the type locality show an intense red terminal band on the pelvic and dorsal fins, which appears more orange in other populations.
Sexual dimorphism is clear once the fish mature. Males bear the goodeid "splitfin" structure — an andropodium, in which the front of the anal fin is notched off after the first roughly seven shortened rays, forming the modified intromittent apparatus used in internal fertilisation. Females have clean, clear fins without the red or orange band and retain the abdominal blotching; they are the plainer sex, deeper-bodied when carrying young.
Habitat
Zoogoneticus purhepechus is endemic to the Mexican states of Jalisco and Michoacán, in the lower Río Lerma drainage of west-central Mexico. Its historical range took in the Río Duero, Laguna de Chapala and the adjacent Río Grande de Santiago, the endorheic lagunas west of Chapala (Atotonilco, San Marcos, Zacoalco and de Sayula), the upper Río Ameca drainage, and the endorheic Laguna Magdalena basin. That range has since contracted by roughly 75 percent from its known historical occurrence points, leaving the species in scattered refuges rather than across a continuous distribution.
The fish occupies lakes, streams, ponds, canals and irrigation ditches over a wide variety of substrates — clay, silt, mud, sand, gravel, organic debris and rock. It tolerates clear to muddy water and from no current to moderate flow, but is usually found in shallow water, typically less than 2 ft and rarely as deep as a metre. The best populations are spring-fed and oxygen-rich, with dense vegetation: green algae, water hyacinth (Eichhornia), Scirpus, Potamogeton, Nasturtium, Chara and Lemna, along with submerged tree roots — willow (Salix) at La Luz and bald cypress (Taxodium) at Lago de Camecuaro.
The type locality is a permanent spring of clear, lentic water forming a small pond of about 1,500 square metres, with a rocky periphery and a muddy bottom, vegetated with Iris, Ceratophyllum and emergent Typha and Scirpus, plus introduced water hyacinth. Native fishes sharing this water include Alloophorus robustus, Chapalichthys encaustus, Goodea atripinnis, Skiffia multipunctata and Poeciliopsis infans — a characteristic assemblage of the goodeid-rich springs of the Mesa Central.
Feeding
The Tarascan splitfin is a visual micro-predator. Its short gut, small pointed mouth and conical teeth all point to a carnivorous diet of small invertebrates — crustaceans and insect larvae taken from the vegetation and water column — rather than the algae-and-detritus grazing of some of its goodeid neighbours. Its reported trophic level of about 2.2 reflects this small-animal diet.
In the aquarium it should be fed as the predator it is. Keepers report success with bloodworms, insect larvae, Daphnia, mysids and brine-shrimp nauplii, supplemented by good-quality flake and granulate. A varied, protein-rich diet supports both condition and breeding, and live or frozen foods are taken eagerly. As with most small, active fishes, several modest feedings suit it better than one heavy meal.
Mating
Like all goodeids, Zoogoneticus purhepechus practises internal fertilisation, but the goodeid arrangement differs in detail from that of the better-known poeciliid livebearers such as guppies and platies. Rather than the rod-like gonopodium of the poeciliids — a long intromittent organ formed from the whole anterior anal fin — the male goodeid bears an andropodium, a "splitfin" in which only the first few anal rays are shortened and notched off from the rest of the fin, forming a shorter copulatory structure. Sperm is transferred to the female through this apparatus.
Courtship in this genus is built around the male's fin colour. Males display the red-to-orange terminal band on the dorsal and pelvic fins to females, and the iridescent body sheen adds to the signal. Detailed behavioural studies specific to Z. purhepechus are sparse, and much of what is inferred about its mating comes from its close relative Z. quitzeoensis; for the Tarascan splitfin itself the published behavioural record is thin, and it is more honest to say the data are sparse than to assert a courtship sequence in detail.
Breeding
Zoogoneticus purhepechus is a viviparous, matrotrophic livebearer — the defining reproductive mode of the goodeids and the feature that most sharply separates them from the poeciliids. After internal fertilisation the female does not simply carry yolk-bearing embryos; instead the developing young draw nourishment from the mother through trophotaeniae, ribbon-like extensions of gut tissue that function as a placenta-analogue and absorb maternal nutrients across the gestation. This true maternal provisioning makes goodeid broods relatively small but the fry comparatively large and well-developed at birth.
Precise breeding figures for Z. purhepechus are not well documented, so much of the seasonal picture is drawn from its close relative Z. quitzeoensis, which breeds from roughly January to April: gravid females and juveniles of all sizes have been recorded in April at Lago de Camecuaro and in November in the Río Duero. The pattern is of seasonal, temperature-cued reproduction rather than the year-round, continuous fecundity of a guppy. Unlike many poeciliids, goodeids do not exhibit superfetation (the carrying of multiple broods at different developmental stages simultaneously) or long-term sperm storage; broods are produced in discrete cycles.
In captivity the species breeds readily when given a proper seasonal rhythm. A winter cool rest below about 68 °F — ideally for two to three months — halts fry production; reproduction resumes when temperatures rise to about 68–70 °F in spring and tails off again above roughly 77 °F. Where multiple sizes of juveniles are present in a well-planted tank, the fry are rarely predated, so a stable colony can be maintained without elaborate fry-rearing infrastructure.
In the aquarium
The Tarascan splitfin is a fish for the keeper who can give it cool, clean, oxygen-rich water rather than the warm tropical defaults of a community tank. A minimum aquarium of around 20 US gal suits a group, set up with dense vegetation and submerged roots for cover but with open swimming space alongside it. The fish wants moderate current and high dissolved oxygen — keepers aim for 8 mg/l or more — and responds well to large weekly water changes on the order of 60–80 percent.
Temperature management is central to keeping this species well. It is a cool-water goodeid that needs a genuine winter rest below about 68 °F, ideally for two to three months, and it can be kept outdoors from spring to autumn wherever daytime water temperature stays above about 63 °F. Sustained warm water above roughly 77 °F is unsuitable and shuts down breeding. Feeding follows its predatory nature: bloodworms, insect larvae, Daphnia, mysids and brine-shrimp nauplii, with flake and granulate accepted as well.
This is not a beginner's livebearer in the way a guppy is. Its cool-water requirement, appetite for live and frozen foods, and need for high water quality place it with the dedicated goodeid keeper, and much of the most reliable husbandry guidance comes through the Goodeid Working Group, the conservation-breeding network that maintains many of these threatened Mexican fishes in aquaria. Keeping a stable captive line is itself a small act of conservation for a species under pressure in the wild.
Conservation
Zoogoneticus purhepechus is assessed as Vulnerable (VU) on the IUCN Red List, under criteria B1ab(i,ii,iii,iv)+2ab(i,ii,iii,iv), in an assessment dated 12 September 2018. The listing reflects a restricted and fragmenting range: historically widespread across the lower Río Lerma, Lake Chapala and the lagunas to the west, the species has lost roughly three-quarters of its former range, and its three recognised evolutionarily significant units are in markedly different states. The Río Lerma/Lake Chapala unit is considered endangered to vulnerable, with its best refuge in four springs draining to the Río Duero; the upper Ameca and Laguna Magdalena unit is endangered; and the Atotonilco–Sayula–San Marcos unit is critically endangered — it was thought extinct after Tanque El Molino dried in 2018, before a new population was found in 2025 in the Teocuitatlán River.
The threats are those facing Mexican goodeids generally, as documented by Lyons and colleagues in their 2019 review: the drying of lakes and springs through water extraction and drought, water pollution from agricultural and urban sources, and the introduction of non-native fishes that compete with and prey on the native fauna. Under Mexico's own NOM-059-SEMARNAT-2010 the species carries no risk category, a gap between the national listing and the IUCN's Vulnerable assessment.
The Goodeidae are among the most imperilled freshwater fish families in the world, and Z. purhepechus is a representative case — a narrowly endemic, habitat-specialised livebearer squeezed by water loss and introduced species in one of Mexico's most heavily used hydrological regions. For this family, captive maintenance by networks such as the Goodeid Working Group is not a hobbyist curiosity but a recognised conservation backstop, and the rediscovery of the critically endangered Atotonilco lineage in 2025 is a reminder that the species' status in the wild is still being actively rewritten.