Topknot Molly

P. kykesis males grow to 13 cm in standard length, while the females attain 10 cm. The body of the fish does not exhibit any specific color other than the black margined scales that may form spots in adult males. The males possess an enlarged, sail-like dorsal fin similar to that of the males of the closely related species P. velifera and P. latipinna as well as a pronounced lower margin on the caudal fin (a "sword"). P. kykesis has fewer rays in the dorsal fin than P. velifera and more lateral scales than either P. velifera or P. latipinna.

Poecilia kykesis ranges from the Usumacinta River drainage and Lake Petén Itzá in Guatemala to Belize and the Yucatan Peninsula in southeastern Mexico. It was reported as an introduced species in the U.S. state of Florida in 1971, probably having escaped from aquaculture or having been released from an aquarium. The fish may have reproduced but apparently did not establish surviving populations, as the species has not been recorded in the United States since 1974. Like other species from the P. latipinna complex, P. kykesis inhabits lakes, pools, tidal lagoons, creeks, and similar shallow waters of brackish to freshwater coastal areas. These waters may be clear or turbid, and the fish occur on substrates including sand, clay, and mud. Some of its preferred habitats feature submerged or emergent aquatic plants.

Like other sailfin mollies, Poecilia kykesis is herbivorous and feeds primarily on cyanobacteria. This dietary preference is posited to have evolved as a result of the transition of the ancestors of the Mollienesia subgenus from freshwater to marine habitats.

Poecilia kykesis is peaceful enough to be kept in a community aquarium, though the males will only develop their distinctive sail fin in a spacious one. In captivity it requires a diet of algae and vegetable flakes and, due to its big appetite, good filtration and frequent partial water changes. The fish will nibble on softer-leaved plants, especially if lacking plant matter in their diet. A good plant cover allows some fry to survive to adulthood.