Taxonomy & naming
Xenotaenia resolanae was described by Clarence L. Turner in 1946 (Occasional Papers of the Museum of Zoology, University of Michigan, No. 495), based on a mature female of about 1.5 in standard length collected by B. C. Turner on 29 March 1939. The holotype (UMMZ-143024) came from the Río Resolana, a tributary of the Río Purificación roughly 25 miles south-west of Autlán, Jalisco — and the specific epithet resolanae commemorates that type locality. The genus name combines Greek xenos, "strange," with Latin taenia, "strip" or "ribbon," in reference to the unusual ribbon-like trophotaeniae of its embryos.
The species belongs to the family Goodeidae, the splitfins, and within it the subfamily Goodeinae — the viviparous Mexican goodeids. Xenotaenia is monotypic: resolanae is its only species. Phylogenetic work places the genus as sister to Ilyodon, with Xenotaenia and Ilyodon together sister to Allodontichthys, a cluster of west-Mexican Pacific-slope goodeids. The Catalog of Fishes (Eschmeyer, CAS) governs the valid name, recognising Xenotaenia resolanae Turner, 1946.
FishBase lists the English common name as Leopard splitfin and the Spanish as Mexcalpique leopardo. The fish has never carried much hobby nomenclature beyond these, reflecting its rarity in the trade and its largely conservation-driven captive history.
Morphology
This is a small goodeid. FishBase gives a maximum of 1.5 in total length for males and unsexed fish and 2 in for females, while Miller et al. (2005) cite a maximum of about 3 in standard length — so the species generally tops out at a few centimetres, with females the larger sex. The body is moderately elongate and laterally compressed, in keeping with a fish of slow stream pools, and the common name "leopard" refers to a variable pattern of dark spotting along the flanks.
The diagnostic male feature is the goodeine andropodium — not the rod-like gonopodium of poeciliid livebearers but a modified anterior portion of the anal fin, in which roughly the first seven rays are shortened and set off by a notch, forming a crowded structure used in internal insemination. Males also tend to carry a somewhat larger dorsal fin than females. Body coloration is variable between individuals and populations and is generally subdued rather than gaudy.
Internally, the species shows the short digestive tract (around 0.85% of total length) and bifid anterior teeth on strong jaws typical of a more carnivorously inclined goodeid — anatomy that matches its observed diet rather than the long gut of a dedicated algae-grazer.
Habitat
Xenotaenia resolanae is endemic to the Pacific slope of west-central Mexico, in the states of Jalisco and Colima. It is confined to two adjacent drainage systems: the Río Purificación (the type drainage) and the Río Marabasco, the latter including the tributary ríos Ayotitlán, Cuzalapa and Patita and the Arroyo Las Marías. Conservation genetics recognise two evolutionarily significant units, one in each basin (Marabasco and Purificación). This is a genuinely restricted-range fish — the basis for its IUCN listing.
The species occupies pools of clear to turbid streams with little aquatic vegetation, over substrates of silt, mud, sand, rock and bedrock. Current ranges from none to moderate, and the fish prefers depths under about one metre, usually somewhat greater than half a metre. Stretches of habitat are partly shaded by streamside trees. Water temperatures recorded in the field during March and April 1975 ranged from roughly 73–78 °F, consistent with the 72–77 °F tropical-freshwater envelope reported by FishBase.
The small size of the range, combined with a history of pollution from sugar-mill discharge, sewage and animal waste in the 1980s, makes the species sensitive to local water-quality and flow disturbances even though its populations have since stabilised.
Feeding
The wild diet of Xenotaenia resolanae appears to be carnivorous to omnivorous, with a leaning toward animal prey. Its short gut, bifid anterior teeth and strong jaws are the anatomy of a fish that takes invertebrates rather than one specialised for scraping algae, and stomach contents and captive observations point to crustaceans, worms and insect larvae as natural foods. FishBase additionally records algae in the diet (Ref. 26133) and assigns a low trophic level of about 2.0, so plant and detrital material likely supplements the animal component depending on what a given pool offers.
In captivity the species is undemanding at the bowl. Keepers report that it readily accepts flake and granule foods alongside frozen and live items such as brine shrimp, with a varied animal-rich menu best supporting condition and breeding. As with most small stream fishes, frequent modest feedings suit it better than infrequent large meals.
Mating
Like all goodeids, Xenotaenia resolanae practises internal fertilisation, but its anatomy differs fundamentally from the poeciliid livebearers (guppies, mollies, platies). Instead of a true gonopodium — a rod-like intromittent organ formed from elongated anal-fin rays — male goodeids possess an andropodium, in which the first several anal-fin rays are shortened and crowded behind a notch. This modified, stiffened front edge of the anal fin is pressed against the female to transfer sperm; it is a structurally distinct solution to the same problem of internal insemination.
Courtship in splitfins centres on the male approaching and positioning alongside the female to bring the andropodium into contact, rather than on the prolonged sneak-and-chase dynamic of guppies. Sexual dimorphism in this species is expressed through the male's andropodium and somewhat larger dorsal fin; body coloration is variable and not strongly dimorphic. Detailed observations of the wild mating behaviour of X. resolanae specifically are sparse, and beyond the general goodeine pattern the species' courtship has not been richly documented.
Breeding
Xenotaenia resolanae is viviparous and matrotrophic — the defining reproductive mode of the Goodeidae. Unlike poeciliids, whose eggs are essentially fully provisioned with yolk before fertilisation, goodeid embryos are nourished throughout development by the mother through trophotaeniae: ribbon- or rosette-like extensions that trail from the embryo's vent and absorb nutrients within the ovarian cavity. It is precisely these structures that give the genus its name (xenos + taenia, "strange ribbon"). There is no superfetation here as there is in some poeciliids; goodeids carry a single developing brood at a time.
Fecundity is small, as is typical of goodeids relative to poeciliids — FishBase notes broods on the order of 10 to 30 — and the young are born as relatively large, fully formed fish; newly recruited juveniles of 0.5 in TL were caught in the field in March and April. In captivity reproduction has been reported year-round except in August and December, suggesting a long but not strictly continuous reproductive period. Goodeid Working Group keepers report spawning at around 68–70 °F that ceases above about 77 °F, and recommend a cool winter rest below 68 °F to pause breeding and condition the fish. Because adults will sometimes predate fry, cover or separation helps raise good numbers.
The combination of internal nourishment, large well-developed neonates and modest brood sizes makes the species slower to multiply than a guppy, which is one reason its captive maintenance depends on coordinated breeding networks rather than casual hobby propagation.
In the aquarium
Xenotaenia resolanae is a specialist's livebearer kept chiefly through the Goodeid Working Group rather than the general trade. It is not delicate so much as exacting about water quality and oxygenation. Recommended housing is a tank of at least roughly 40 US gal, low and wide rather than tall, with moderate current and high dissolved oxygen (on the order of 8 mg/l or more), plus large weekly water changes of 60–80%. These are stream fishes that reward clean, well-moving, well-aerated water.
In temperament the species is not shy and settles well, though some intraspecific male aggression occurs and adults may predate fry, so structure and cover in the tank help. It accepts prepared, frozen and live foods readily. A seasonal regime works well: keep the fish cooler (below about 68 °F) in winter to rest them, then allow breeding at 68–70 °F in the warmer months, noting that spawning stops above about 77 °F.
For an aquarist, the meaningful point is conservation context: this is a Vulnerable, restricted-range Mexican endemic whose hobby presence is essentially an ex-situ safeguard. Keeping it well means maintaining genetically managed lines through the working-group system rather than treating it as an ornamental community fish.
Conservation
Xenotaenia resolanae is assessed as Vulnerable (VU) on the IUCN Red List (species ID 191716), under criteria B1ab(i,ii,iii,iv)+2ab(i,ii,iii,iv), with the assessment dated 14 March 2018. The listing reflects its restricted range — a single small endemic confined to the Río Purificación and Río Marabasco drainages of Jalisco and Colima — rather than a documented steep decline. Across roughly twenty historical localities the populations are small but, per Lyons et al. (2019), broadly stable, having recovered after the heavy pollution episodes of the 1980s.
The historical threats were water-quality driven: sugar-mill (ingenio) discharge, sewage and animal waste degrading the small streams the species depends on. With those pressures eased, the fish is now characterised as "vulnerable but stable." Notably, Mexico's national listing NOM-059-SEMARNAT-2010 places it in no category of risk, a discrepancy with the IUCN assessment that underscores how a narrow range alone can drive a global Vulnerable rating.
As with many west-Mexican goodeids, the practical safeguard against future loss is twofold: protecting the integrity and water quality of its two home drainages in the wild, and maintaining genetically managed captive lines through hobbyist conservation networks such as the Goodeid Working Group. For a monotypic genus, that ex-situ insurance carries particular weight.