Poecilia velifera

Poecilia velifera, known as the Yucatan molly, is a poeciliid fish that lives in coastal waters of the Yucatan Peninsula in Mexico. The species is best known for the enlarged dorsal fin and ornamentation of some of its males as well as its social behaviors.

Poecilia velifera reaches up to 15 cm (5.9 in) in total length. It belongs to sailfin mollies and is most closely related to P. latipinna, though larger overall and with a higher and longer dorsal fin in males. Large males flare their dorsal fin for females in an elaborate courtship display and also when challenging other males. Smaller males are not ornamented; instead, they hide among females and mate sneakily.

The Yucatán molly's preferred habitats are salt and brackish waters, especially salt marshes and mangrove forests, but it also occurs in freshwater cenotes. It is primarily herbivorous, feeding by browsing submerged surfaces, and is in turn preyed upon by other fish, birds, and crocodiles. While classified as a vulnerable species because of threats in its native habitat, the Yucatán molly has also been introduced to various South American and Asian countries.