Red-tailed Goodeid

Xenotoca eiseni, the Red-Tailed Goodeid, is a member of the Goodeidae family — a group of livebearers endemic to Mexico's Mesa Central that reproduce differently from poeciliid livebearers. Goodeid embryos are nourished by trophotaeniae, specialised structures analogous to a placenta, and fry are born large and well-developed.

Males display a vivid orange-red flush on the caudal peduncle that contrasts sharply with the olive-grey body — a signal used in courtship and male-male competition. Females are larger and less colourful. In the wild, Xenotoca eiseni is critically endangered due to habitat destruction and invasive species, making captive populations maintained by dedicated keepers genuinely important for conservation.

This species is best kept in a species or goodeid-specialist tank with Mexican endemic companions such as other goodeids. It has a slightly feisty temperament and may nip fins of slower-moving fish.

Water: 18–24 °C, pH 7.0–8.0, moderate to hard; prefers cooler temperatures than most livebearers. Tank: 80 L species tank; robust plants as they may nibble soft vegetation; moderate flow. Feeding: Omnivore with herbivore tendency; algae flake, spirulina, blanched vegetables, and quality pellets. Breeding: Small litters of 5–25 large fry; trophotaeniae fry easy to raise; gestation 55–65 days. Compatibility: Species or goodeid tank; avoid delicate fish as males can be nippy and assertive.