San Marcos Redtail Splitfin Xenotoca doadrioi

The San Marcos Redtail Splitfin was, until 2016, considered the same as the Redtail Splitfin (X. eiseni), a goodeid native to western central Mexico around the Santiago River area. It and another (X. lyonsi) are now considered separate species. The male of all 3 has the bright orange-red tail.

Females are plain, larger and grow to some 7cm long.

The San Marcos inhabits the Magdelena Lagoon. It is critically endangered.