Poecilia Mexicana

Poecilia mexicana, commonly known as the shortfin molly or Atlantic molly, is a species of poeciliid fish native to fresh and brackish water in Mexico and Guatemala. One population is found in caves and known as the cave molly.

Poecilia mexicana
Atlantic molly male (top) and female (bottom)
Conservation status
Least Concern  (IUCN 3.1)
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Actinopterygii
Order:	Cyprinodontiformes
Family:	Poeciliidae
Genus:	Poecilia
Species:	P. mexicana
Binomial name
Poecilia mexicana Steindachner, 1863
Synonyms
Poecilia cuneata Garman, 1895 Poecilia limantouri Jordan & Snyder, 1899

The maximum standard length of this fish is 11 cm (4.3 in). It typically grows to a total length 4 cm (1.6 in).

The fish lives in tropical freshwater and brackish water habitats. The shortfin molly is considered benthopelagic. It lives in a pH range between 7.0 and 7.5 at temperatures between 22 and 28 degrees Celsius. The species does not migrate. It is an invasive species in the Muddy River of Nevada, USA.

Speciation

In two case studies in Cueva del Azufre and Cueva Luna Azufre in Tabasco, Mexico, the Atlantic molly is experiencing speciation. It is occurring between cave and surface populations as well as between habitats of varying sulfur concentrations.

The fishing industry has no interest in harvesting the species. However, it is sold commercially for aquariums. Occasionally, the shortfin molly is used as bait.

Franz Steindachner first described the species in 1863. Poecilia refers to the Greek word poikilos, which means "with a lot of colours". Common names include "shortfin molly" and "Atlantic molly." The type specimen was found in Orizaba, Mexico.