Rosen 1960.

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

Both sexes 50 mm. Smaller morph 10 mm smaller.

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

• X.montezumae cortezi Rosen 1960.

Populations

Arroyo Matlapa at Comoca, 3·2 km north of Axtla in the Rio Panuco Basin, state of San Luis Potosi, Mexico. Collected on 14-15th April 1939 by Myron Gordon, S.Coronad & H.F.Gandy. Holotype male 38·5 mm SL, female 34·9 mm SL.

Distributed south of the Rio Tampaon. This sp.has been collected in the Rio Choy, Moctezuma, Axtla, San Pedro & Candelaria.

Streams with good current flowing over rocky bases. Hides under these rocks.
Derek Lambert reported that in the headwaters of the Rio Tancuilin at Rio Verdito (state of Queretaro) the sp. was found in water with a temperature of 13°C.

Derek Lambert suggested a water temperature of around 22°C for breeding as higher temperatures speeded up maturity leaving fish smaller.
Dr.Klaus Kallman of the New York Aquarium conducted experiments on brood drop periods from 21 - 32 days.
A good brood size is reckoned to be around 30. The record I understand stands at 76.

Two size morphs have been identified according to Lambert in 'Platies & Swordtails' which apparently only becomes evident when raising in a mass culture. Under these conditions the smaller morph is 10 mm smaller than the larger morph.