Yucatán Molly, Poecilia velifera
Yucatán Molly, Poecilia velifera. Underwater photographs taken in Cenote Azul, Quintana Roo, December 2020. Photographs and identification courtesy of Bob Hillis, Ivins, Utah.
The Yucatán Molly, Poecilia velifera, is a member of the Livebearer or Poeciliidae Family, that is also known as the Great Sailfin Molly and he Sailfin Molly and in Mexico as topote aleta grande. Globally, there are forty species in the genus Poecilia, of which six are found in Mexican freshwater systems that drain into both the Atlantic and the Pacific Oceans. This fish is the iconic livebearer and the symbol of the American Liverbearer Association.
The Yucatán Molly has an oblong moderately robust body that is compressed at the rear. They have a moderately robust head and body that is moderately compressed at the rear. They are a light pearly gray to tan in color. The males have 8 to 10 rows of small red-brown spots on their scale rows along the body. Their caudal fin has rows of small brown and pearly spots and a dark margin; their dorsal fin is dark with 4 or 5 rows of pearly spots. In a limited number of males the fan is disproportionately large, trapezoid in shape, with the upper edge being distinctly longer than the lower, and is covered with fine, bright and crisp blue, orange and red markings over its body. The juveniles are drab silvery white in color. They have small terminal slightly oblique mouth that opens in the front with a slightly projecting lower jaw that is equipped with an outer row of large backward curved teeth with expanded tips and several rows of small pointed teeth. The Yucatán Molly is sexually dimorphic with females being less colorful and larger than males with different behavioral patterns. The males have an elongated anal fin that is a sex organ and their pelvic fins are swollen and elongated. Their anal fin has 9 rays and originates well behind the dorsal fin; their caudal peduncle is narrow and their caudal fin is rounded; their dorsal fin has 16 to 20 rays, has a long base and located before the pelvic fins and is enlarged in both sexes but is high and sail-like in males; the pectoral fins are high on the flank; and the pelvic fins originate well behind the pectoral fins. They are covered with smooth scales.
The Yucatán Molly is a shallow water species that is found in coastal habitats that are either brackish or freshwater within karstic sinkholes, mangrove channels, coastal lagoons and salt marshes at elevations below 20 m (66 feet) with water temperatures between 25°C (77°F) and 28°C (83°F). They reach a maximum of 15.2 cm (6.0 inches) in length. They are known primarily for the spectacular displays put on by the males during courtship that includes “flaring” whereby the males spread their huge dorsal fin and the extreme size variations of mature males. Reproduction involves internal fertilization with gestation periods of 3 or 4 weeks. Each female can produce broods of 10 to 30 live young. The females have the ability to store sperm and give birth on multiple occasions throughout the year. The young mollies aggregate in schools of similarly-sized fish. They are omnivores that grazer continually on filamentous algae and diatoms as-well-as crustaceans and insects. In turn they are preyed upon by various pelagic and surface predatory fish as well as numerous seabirds, including herons. The Yucatán Molly is poorly studied with very limited information available about their lifestyle and behavioral patterns including specific details on age, growth, longevity, movement patterns, diet, habitat use, and reproduction.
The Yucatán Molly is easily confused with the Sailfin Molly, Poecilia latipinna (larger; 15 dorsal fin rays).
The Yucatán Molly is a resident of the coastal freshwater systems of the Yucatán Peninsula and found in the states Campeche, Quintana Roo, and Yucatán.
From a conservation perspective the Yucatán Molly is currently considered to be VULNERALBE due to their limited native range and limited number of known locations and the on-going loss of native habitat due to human development. The species has been a focus of the aquarium trade for years but are very difficult to manage and maintain and interest has significantly diminished noting that they are generally considered to be the most spectacular of the aquarium fishes and are well-behaved, non-aggressive and do not eat their fry.