Butterfly splitfin
A critically endangered livebearing fish from Mexico.
The butterfly splitfin is a small livebearing fish native to the Ameca River drainage in Mexico. Once common in a limited area, it is now critically endangered due to habitat loss and declining captive stocks. It features distinct sexual dimorphism and unique reproductive traits.
- Only member of the genus Ameca
- Females grow larger than males
- Young nourished by trophotaenia
- Critically endangered in the wild
- Requires hard alkaline water
What it is
This bony fish belongs to the splitfin family and is the only member of its genus. Males display striking colours with black-edged dorsal and tail fins, while females are more subdued with ochre tones. The species is named for its attractive appearance. Males possess a modified anal fin called an andropodium for mating. Females grow larger than males, reaching up to ten centimetres in length.
Where it lives
Historically, this fish lived in a small area of the Ameca River drainage near Teuchitlán in Jalisco. Recent surveys have located individuals in nearby springs and rivulets up to one hundred kilometres away. The natural environment features limestone bedrock, creating hard and alkaline water conditions. Temperatures remain stable between twenty and thirty degrees Celsius throughout the year.
How it lives
These social fish form loose dominance hierarchies, with dominant males showing brighter colours. They are strong swimmers that thrive in groups within large tanks or natural springs. Their diet includes algae, detritus, and small live prey. In captivity, they benefit from plant matter such as lettuce or spinach if algae are scarce. They coexist with other native species and some introduced fish in their remaining habitats.
Breeding and life cycle
Reproduction involves internal fertilization, typical of livebearers. Females reach maturity at six months and can give birth every six to ten weeks. Unborn young are nourished by trophotaenia, structures similar to umbilical cords. Fry are born fully developed and may measure up to twenty millimetres. Courtship involves males tilting their heads downward and shaking their bodies to attract females.
Fish and people
Aquarists value this species for its beauty and algae-eating habits. It requires clean, well-aerated water with specific hardness levels. While popular in the hobby, captive stocks have declined recently. Zoos and public aquariums maintain colonies to support conservation. The fish can be aggressive towards smaller tank mates but pairs well with hardy cichlids. Outdoor ponds are suitable in temperate climates during summer.
Status and threats
The International Union for Conservation of Nature lists the species as critically endangered. Wild populations persist in low numbers in springs and rivulets. A remnant group was found in a dammed waterpark, though its current status is uncertain. Introduced populations in Nevada were reported in the early nineteen-eighties but may not survive. Habitat degradation and reduced hobbyist interest threaten its long-term survival.
Questions people ask about Butterfly splitfin
What does the butterfly splitfin eat?
It is an omnivore that consumes algae, detritus, and small live prey. In captivity, it accepts commercial fish food and benefits from vegetable additions like spinach or green peas to ensure proper nutrition and vitality.
How big do butterfly splitfins get?
Females are the larger sex, growing up to ten centimetres under good conditions. Males are smaller, typically reaching a maximum total length of seven to eight centimetres when fully mature.
Are butterfly splitfins aggressive?
They can be aggressive, especially in high-density tanks with little decoration. Dominant males chase each other, and they may bully small, delicate fish like guppies. They are best kept with hardier species in spacious environments.
Where is the butterfly splitfin found?
It is native to the Ameca River drainage in Jalisco, Mexico. Wild populations are now critically endangered and restricted to a few springs and rivulets. Some introduced individuals were found in Nevada decades ago.
Good reading and sources
- Butterfly splitfin on WikipediaEncyclopedia
- More photos on Wikimedia CommonsPhotos
- Wikidata recordOpen data
The facts on this page come from the Wikipedia article "Butterfly splitfin", written by its contributors and used under the CC BY-SA 4.0 licence, and from its Wikidata record (CC0). EveryFish rewrote the text in its own words, with AI assistance, and compares every page with the article to make sure no passage is copied. It may be reused under the same CC BY-SA 4.0 licence with a link back.
It may contain mistakes, and figures change over time. Nothing here is investment or buying advice. If something is wrong, tell us. Last refreshed 2026-11-15.
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