Xenotoca lyonsi, the Tamazula redtail splitfin, is a bony fish species in the goodeid family. Until 2016 it was considered to be a variant of the redtail goodeid, X. eiseni. A 2016 study by Omar Dominguez-Dominguez, et al. split the redtail goodeid into three separate species: X. eiseni, X. doadrioi and X. lyonsi.[1]
The IUCN lists Xenotaca lyonsi as critically endangered.[2]
Xenotoca lyonsi is endemic to the Coahuayana River drainage in Jalisco, Mexico.[3]
Xenotoca lyonsi reaches a standard length of 5cm (02inches).[4] Males are more colorful than females, with red caudal fin and caudal peduncle, and blue area in front of the red.[4] Females are brownish or brownish grey, and sometimes have a horizontal dark band across the middle of the body.[4]