Furry Diary

Not furry, but we like them anyway.

Redtail Splitfin

Xenotoca eiseni

Also called Redtail goodeid, Mexcalpique cola roja

SpeciesShort profile

From West-central Mexico: the Río Grande de Santiago basin and waters near Compostela, Nayarit.12

At a glance the quick version

Length6 to 7 cm213
Sizesmall
Hardy
Striking red-orange tail on males
Tolerant of a wide temperature range
31

Looks how to spot one

Scaled goodeid livebearer

A sturdy, deep-bodied livebearer. Males develop a raised hump behind the head that grows with age and use a notched anal fin (andropodium) for mating.13

ColoursOlive-brown backBlue-black band along the side (males)Red-orange tail and tail base (males)Yellowish-white bellyPlainer females13

Personality what they are like

Character varies between individuals: some live calmly in a community, while others nip fins. Keeping them in a group or a species tank works best.31

Daily activity how busy a day looks

Active and bottom-to-midwater swimming; appreciates room to move.32

Grooming and care the hands-on bits

Undemanding and hardy. Include plenty of vegetable food and keep the water clean.13

Home where they are happiest

Aquarium from about 60 x 30 x 30 cm (around 54 litres). Water 15-30 °C, pH 6.0-8.0, 10-20 dGH; harder, alkaline water preferred.312

Food basics what goes in the bowl

Unfussy omnivore that needs vegetable matter in the diet alongside flake and frozen foods.13

Company who they like around

Best in a group of its own kind or a species tank; avoid slow, long-finned tankmates.31

The story where it all began

Rutter described the species in 1896 and named it after Gustav Eisen, curator of marine invertebrates at the California Academy of Sciences. It is one of the best-known goodeids in the aquarium hobby.12

Fun facts for the dinner table

  1. 1

    Mothers feed developing young through ribbon-like trophotaeniae, which work much like an umbilical cord.1

  2. 2

    Fry are about 15 mm long at birth, large for a livebearer.1

  3. 3

    Wild fish tend to pair with mates of similar size.1

  4. 4

    Females give birth roughly every two months.2

Recognised by the official bits

IUCN Red List
Endangered (assessed 2018)2
Taxonomy
Family Goodeidae; described by Rutter in 18961

The care rhythm Furry Diary remembers it for you

A typical home-care rhythm for a Redtail Splitfin. It is our own starting plan, not a vet's advice, and you can change every line in the app.

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Where this comes from

Every breed page shows where each fact comes from. If we got something wrong, sorry, we are pet people, not a science magazine. Tell us at [email protected] and we will fix it.

  1. Wikipedia: Xenotoca eiseni en.wikipedia.orgused for range, colour, history, facts
  2. FishBase: Xenotoca eiseni fishbase.seused for size, environment, IUCN, reproduction
  3. Seriously Fish: Xenotoca eiseni seriouslyfish.comused for tank size, water, behaviour

Checked 2026-09-30. Text is written in our own words from these sources.