Donn E. Rosen 1960.

Middle-American poeciliid fishes of the genus Xiphophorus.
Bull. Fla. St. Mus. Biol. Sci 5 (4): p 57-242.

Males 25 - 40 mm; females 40 mm.

Member of the group comprising alvarezi, birchmanni, continens, cortezi, helleri, malinche, montezumae, multilineatus, nezahualcoyotl, nigrensis, pygmaeus & signum.
Clade pygmaeus

• Xiphophorus pygmaeus nigrensis Rosen 1960.

Populations

• Rio Choy, El Abra near Ciudad Valles.

The Rio Choy has also been referred to as the Rio Florido.

Nacimiento del Rio Choy, 4 km north of Hotel Taninul, 3 km north of Route 110, Valles Tampico, San Luis Potosi State, Mexico. The holotype was collected by D.E.Rosen, M.S.Gordon & M.Gordon on the 19th January 1957. This measured 29 mm SL.

At present this species is known only from a single outlet from the El Abra mountain. Extensive photographs are shown below.

The biotope is clear & fast flowing & originates from inside a cave under Mount El Abra. The biotope further downstream is reportedly slower flowing with dense aquatic plant growth especially near the banks.

Dave sent me loads of photos of the location Rio Coy, El Abra near Ciudad Valles & some photo's are shown below. See also Rio Choy biotope page.

A spring originates from inside this cave which feeds the biotope.

Females drop on a monthly cycle. Brood sizes are relatively small being only 2 for smaller females & up to 20 for more mature females. These females are thought to be fertile between 3 - 8 months of age.
Large morph males sex out at 5 months.
It is important to remove virgin females from the brood & mate with the larger form males as the small form will become dominant with the loss of the larger form. Females are not affected by this sex-linked gene which is only known in males.

This has proved to be a challenge sp. requiring very clean water conditions. They have been reported to be susceptible to parasitic infections. Large pH changes should be avoided as this can be fatal.
Two morphs are known in the species. The photo at the top of the page is the large morph. A smaller morph male is known with a smaller sword. I have only seen photo's of fish at 3 months of age but they had brown spots in the upper half of the body above the distinctive horizontal line.