Taxonomy & naming
Skiffia lermae was described by the American ichthyologist Seth Eugene Meek in 1902, in his foundational monograph A Contribution to the Ichthyology of Mexico (Field Columbian Museum, Zoological Series). Meek erected the genus Skiffia in the same work, naming it in honour of Frederick James Volney Skiff, the first director of the Field Columbian Museum — Skiffia translating loosely as "Skiff's one." The holotype (FMNH 3616, a 2 in fish) was collected by Meek and F. E. Lutz in May 1901 from Lago de Pátzcuaro, near the town of Pátzcuaro in Michoacán, which stands as the species' type locality.
The specific epithet lermae refers to the Río Lerma basin. The name reflects a geographic error on Meek's part: he believed Lago de Pátzcuaro drained into the Lerma system, when in fact Pátzcuaro sits in its own closed (endorheic) basin separate from the Lerma. The fish nonetheless does occur across the true middle Lerma drainage, so the name has proved apt in the end. Two names have fallen into synonymy beneath it — Skiffia variegata Meek, 1902 (from Lago de Zirahuén, a population now extinct) and Goodea lermae Regan, 1907.
The genus Skiffia belongs to the family Goodeidae, subfamily Goodeinae, the splitfins of the Mexican highlands, within the order Cyprinodontiformes. Eschmeyer's Catalog of Fishes treats Skiffia lermae Meek, 1902 as the valid name. The species is sometimes partitioned into evolutionarily significant units (ESUs) by conservation geneticists — four are recognised across its remaining range — reflecting the genetic divergence that has built up among its now-isolated refuge populations.
Morphology
Skiffia lermae is a small, compact goodeid. Reported maximum sizes vary by source and method: FishBase gives about 2 in total length for males and 2 in for females (after Wischnath's Atlas of Livebearers), while Miller and colleagues report a maximum standard length of around 2.5 in. Length at first maturity is roughly 1 in. The body is moderately deep and laterally compressed, in keeping with a fish of quiet, vegetated shallows.
The ground colour is an olive to brownish-grey, the basis of the common names "olive skiffia" and tiro olivo. Sexual dimorphism is pronounced, particularly in breeding condition. Males carry a larger, notched dorsal fin with a serrated anterior edge, and — like all male goodeids — bear the andropodium, a modified anal fin in which the first several rays are shortened and set off by a distinct notch (the "split" of the splitfins). In breeding dress, males develop a dark, often blackened head and a yellow-to-orange wash over the caudal peduncle and body, while females show a yellowish belly. These colours are mood-dependent and fleeting: a disturbed or stressed fish can lose its breeding colour within minutes.
Habitat
Skiffia lermae is endemic to central Mexico, recorded historically across the states of Michoacán, Guanajuato and Querétaro. Its former range spanned the middle Río Lerma and several adjacent basins: the Río Grande de Morelia drainage (including Lago Cuitzeo and Presa Cointzio), Laguna Yuriria, the spring systems of La Mintzita, La Maiza and San Cristóbal, Laguna Zirahuén, Lago de Pátzcuaro, the Río Angulo and Lago Zacapu, and the middle Lerma tributaries such as the Río Turbio and Río Laja, with a single outlying report from the Río San Juan of the Pánuco drainage.
The fish favours quiet waters — the shallow margins of lakes, spring-fed ponds, canals and small creeks — typically less than a metre deep, with no to slow current. It tolerates clear or turbid water over bottoms of mud, sand, gravel and decaying organic matter, and is closely associated with submerged and emergent vegetation: water hyacinth (Eichhornia), duckweed (Lemna), bulrush (Scirpus), Salvinia, watercress (Nasturtium) and pondweed (Potamogeton). Adults in particular prefer thickly planted shorelines.
That range has collapsed. Over roughly the past half-century the species has retreated to perhaps six remaining sites, the most important being Lake Zacapu in the Lerma basin, the Molino de Chapultepec springs in the Pátzcuaro basin, and the La Mintzita springs in the Grande de Morelia basin. One unit, restricted to the Río Laja system, is confined to the Charco del Ingenio reserve near San Miguel de Allende and is regarded as critically imperilled.
Feeding
Skiffia lermae is an omnivore with strongly herbivorous leanings — FishBase places it at a low trophic level of about 2.1, and its gut is long for its size (the intestine measuring roughly two to three and a half times the body length), the digestive signature of a plant-and-detritus grazer. In the wild it works over the aufwuchs, the film of algae and micro-organisms coating submerged surfaces, grazing it from the stems of bulrush and from rocks, and it will also take small insects from the surface.
In captivity it accepts a broad diet built around that grazing habit. Keepers offer algae and aufwuchs where it can be cultured, supplemented with blanched vegetables, small live and frozen foods such as Daphnia and newly hatched brine shrimp, and good-quality flake or granular foods. A vegetable-rich diet suits its physiology and helps maintain condition and colour.
Mating
Like all goodeids, Skiffia lermae practises internal fertilisation, but its anatomy differs from the more familiar poeciliid livebearers such as guppies and mollies. Where a male poeciliid uses a true gonopodium — a rod-like intromittent organ formed from the whole anal fin — the male goodeid transfers sperm using the andropodium, the notched, partly separated front portion of the anal fin that gives the splitfins their name. Sperm is delivered in packets (spermatozeugmata) rather than as a tube-driven stream.
Courtship plays out in the planted shallows the fish inhabits, with breeding males advertising their readiness through their darkened heads and yellow-orange flush. The recorded reproductive season runs at least from February to May, when pregnant females and newborn fry are observed in the wild. Recent research underscores how sensitive this reproduction is to water quality: a 2024 study found that realistic, field-relevant concentrations of nitrate measurably depressed reproductive indicators in female S. lermae — a direct line drawn from agricultural and urban pollution to the species' decline.
Breeding
Skiffia lermae is viviparous in the full goodeid sense: the developing embryos are not merely incubated but actively nourished inside the female through trophotaeniae, ribbon-like extensions that function as a placenta-like nutrient-transfer structure. The young are therefore born comparatively large and well-developed, as fully formed miniatures ready to swim and feed. In the wild, broods of fry have been seen swimming near the surface in loose groups of roughly three to fifteen.
Unlike many poeciliids, goodeids generally do not produce huge serial broods from stored sperm; brood sizes are modest and the investment per young is high. One trait makes the species a forgiving colony breeder, however: the adults usually do not hunt their own fry, so young raised in a well-planted tank stand a good chance without being separated. Reproduction is strongly seasonal and temperature-cued — spawning begins as water warms to around 68 °F in spring and tapers off above about 75 °F — so a cool winter rest is part of the natural cycle rather than an interruption of it.
This species does not display superfetation (the carrying of multiple broods at different developmental stages simultaneously), a phenomenon documented in some other livebearers; S. lermae instead follows a single seasonal reproductive pulse keyed to spring temperatures.
In the aquarium
Skiffia lermae is an uncommon fish in the hobby, kept very largely by conservation-minded specialists — indeed FishBase notes it is "cultivated almost exclusively in scientific institutions" — and groups such as the Goodeid Working Group maintain it expressly as an ark population against extinction in the wild. It is not difficult to keep so much as exacting about a few conditions that mirror its cool, clean, highland habitat.
Keepers recommend a tank of at least 15 US gal, and ideally a broad, shallow layout (around 10 in of water depth) with moderate current and high oxygenation — dissolved oxygen of roughly 8 mg/l or more suits it. The species is intolerant of warm, stale water: sustained temperatures above about 75 °F bring disease and shortened lifespans, so it wants cooler conditions than tropical livebearers and benefits from a genuine winter cool-down below 68 °F for two to three months, which also paces its breeding. Large, frequent water changes — on the order of 60 to 80 percent weekly — keep the water as clean as the fish demands. Fed on algae and aufwuchs, blanched vegetables, Daphnia, brine shrimp nauplii and prepared foods, and given the plants it likes to graze and shelter in, it makes a rewarding subject for aquarists willing to treat its upkeep as a small act of conservation.
Conservation
Skiffia lermae is assessed as Endangered on the IUCN Red List (criteria B1ab(i,ii,iii,iv)+2ab(i,ii,iii,iv); date assessed 13 March 2018). In Mexico it is additionally listed under NOM-059-SEMARNAT-2010 as Amenazada (threatened). Both listings reflect the same trajectory: a once-widespread highland fish reduced over decades to a handful of fragmented refuges.
The drivers of decline are the familiar ones of the Mexican Plateau's freshwater fauna — desiccation and pollution of lakes and springs from agriculture and urban growth, the spread of invasive species, and the steady loss of the clean, vegetated, well-oxygenated shallows the species needs. The 2024 finding that ordinary field concentrations of nitrate suppress reproduction in this species puts a fine point on the pollution threat: even where water remains, its chemistry may no longer permit the fish to breed.
Because its remaining wild strongholds are so few and so vulnerable, captive maintenance has become a genuine pillar of the species' survival. Conservation breeding networks keep distinct lineages in cultivation precisely so that, should a wild refuge fail, the genetic line is not lost with it — making Skiffia lermae one of those fishes for which the aquarium and the field have become two halves of the same conservation effort.