Butterfly Splitfin

Butterfly Goodeid or Butterfly Splitfin, was formerly found throughout the Ameca River drainage in Mexico; the type locality is Rio Teuchitlán in the vicinity of Teuchitlán, Jalisco. The species was only ever found in an area about 10 miles (15 km) in diameter.

Today, the species is rated as extinct in the wild by the IUCN, though it is noted that this assessment is obsolete: a remnant population has been found to persist in El Rincón waterpark near the town of Ameca. Possibly, it also exists in a feral state in the USA; individuals apparently derived from escaped or introduced captive stock were met with in southeastern Nevada. For some time, it was a popular fish among aquarists, but unfortunately hobbyist stocks have declined quite a lot more recently, placing its survival in jeopardy.

As its common name implies it is indeed quite an attractive fish. A dominant mature male specimen will have a large dorsal fin which like the caudal fin is washed with black. A yellow band stretches along the caudal's back margin. The body of both sexes is ochre, with silvery sides and a brownish back, which in males usually have numerous glittering metallic scales. Females and immatures having black dots on the sides and ochre fins. The fins of males intensify in color when they are excited, and depending on their mood, they can show more or less strongly a black band along the side. For the first two weeks or so after birth, the young are entirely silvery.

Males can also be told apart from females because they have the anal fin's front part split off and transformed to a blunt, flexible andropodium used for mating. As usual in live-bearers, males are the smaller sex, reaching some 3 in (7-8 cm) total length at best, with females being able to grow up to 4 in (10 cm) TL under good conditions.

Courtesy Wikipedia