Butterfly splitfin

The butterfly splitfin or butterfly goodeid (Ameca splendens) is a bony fish from the monotypic genus Ameca of the splitfin family (Goodeidae). It was formerly found throughout the Ameca River drainage in Mexico; the type locality is Rio Teuchitlán in the vicinity of Teuchitlán, Jalisco, near the town of Ameca. The species was historically only found in an area about 10 miles (15 km) in diameter but in the early 21st century, searches have found it in a few other locations in the region, up to 100 km away at Cuyacapán.

Today, the species is rated as critically endangered by the IUCN. A remnant population was found to persist in El Rincón waterpark, where the Rio Teuchitlán's springs have been dammed for bathing, between Teuchitlán town and he prehistoric site of Guachimontones, but it is unclear if this population still survives. Possibly, it also exists in a feral state in the United States; individuals apparently derived from escaped or introduced captive stock were found in Rogers Warm Spring in southeastern Nevada, but this was in the early 1980s, and the species' persistence there is unclear.

As of 2019, it is still found in low numbers in some other rivulets and springs of the Ameca River drainage. For some time, it was a popular fish among aquarists, but hobbyist stocks have declined more recently, placing its survival in jeopardy.