Redtail Splitfin (Xenotoca eiseni)

The Redtail Splitfin (Xenotoca eiseni), also known as the Red-Tailed Goodeid or Sheepshead Goodeid, is a livebearer belonging to the family Goodeidae, native to the Río Grande de Santiago basin in Jalisco and Nayarit, Mexico. Unlike common livebearers such as guppies and platies (family Poeciliidae), goodeid livebearers are characterized by their internal fertilization using an andropodium (a modified anal fin), a short gestation, and the birth of large, nutritionally advanced young connected to a trophotaeniae (a placenta-like structure).

Males of X. eiseni display a striking orange-red caudal peduncle and posterior body, while females are more drab olive-brown. The split or forked appearance of the tail base gives the species its common name. Adults reach 7–8 cm in length.

This species is listed as Extinct in the Wild or Critically Endangered in some of its native range due to habitat destruction and introduced species. Captive populations maintained by hobbyists and conservation programs are therefore significant for the species' survival.

Redtail Splitfins are hardy and undemanding in terms of water chemistry, preferring neutral to slightly alkaline, moderately hard water. They are omnivorous with a preference for vegetable matter. They can be kept in groups or pairs and are generally peaceful, though males may compete with each other.

Water Parameters: Neutral to slightly alkaline water: pH 7.0–8.0, temperature 20–26°C, GH 10–20. They are from the Mexican highlands and appreciate cooler, moderately hard water. Avoid very soft or acidic conditions. Good water quality is important for fry health.

Tank Setup: A 60-liter aquarium for a small group. Provide a well-planted setup with plenty of vegetated areas for fry refuge. Include floating plants for cover. A gentle filter is suitable — they don't require strong flow. The tank should be temperature-stable.

Feeding: Omnivores with a preference for plant matter. Offer high-quality flake food, spirulina flakes, blanched vegetables (zucchini, spinach), algae wafers, and small live or frozen foods. Feed twice daily. Vegetable content is important for long-term health.

Tankmates: Generally peaceful in appropriate setups. Can be kept with other similarly-sized peaceful fish. Males may compete mildly. Keep 1 male to 2–3 females ratio. Avoid very aggressive species. Compatible with White Cloud Mountain Minnows and other cool-water species.

Breeding: Livebearers giving birth to 5–20 large, well-developed fry after approximately 60-day gestation. Fry are large enough to accept finely crushed flake food immediately. Provide dense planting to protect fry from adults.