Amazon Molly, Poecilia formosa
Amazon Molly, Poecilia formosa. Fish caught from the Meadow Hotsprings, Meadow, Utah, August 2019. Length: 5.8 cm (2.3 inches). Catch, photograph and identification courtesy of Luke Ovgard, Klamath Falls, Oregon.
The Amazon Molly, Poecilia formosa, is a member of the Livebearer or Poeciliidae Family, that is also known as the Amazon Warrior, and in Mexico as topote amazona. 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 Ocean. Their common name, derived from Greek Mythology, Amazon Warrior, is reflective of their all female society. They are of keen interest to the scientific community as they represent a keystone in evolutionary genetics.
The Amazon Molly is small in stature and has an oblong moderately robust body that is compressed at the rear. They have a dull, silvery diamond-shaped color pattern with rows of black or brown spots on the sides. Their head is moderately robust and flattened dorsally with a pointed snout and a small terminal mouth that opens at the front with a projecting lower jaw and a protractile upper jaw. Their anal fin origin is behind the dorsal fin origin; their dorsal fin has 10 to 12 rays with a base that is more than one-half the predorsal length; their pectoral fins are high on the body and large and fan-like; and, their pelvic fins are small, short and end well before the anus. They reach a maximum length of 9.6 cm (3.8 inches). They are covered with large smooth scales.
The Amazon Molly is non-migratory inconspicuous freshwater or brackish non-vegetated water species that is found at depths up to 3 m (10 feet) in waters with temperatures between 25°C (75°F) and 29°C (85°F). They tolerate a variety of habitats from sea level to upland inland waters of tranquil rivers, coastal lagoons, and pools of smaller streams that are clear to muddy with boulders, clay, gravel, oyster shell, sand or silt. Reproduction is viviparous and they are the subject of scientific interest as they reproduce via gynogenesis, which is sperm dependent parthenogenesis, with all individuals being females. The females mate with a male Mexican Molly, Poecilia sphenops, Sailfin Molly, Poecilia latipinna, or Shortfin Molly, Poecilia mexicana, or Tamosí Molly, Poecilia latipinna, with the sperm acting as a trigger for reproduction with each female producing 60 to 100 clones of herself every 30 to 40 days. Thus, for survival the Amazon Molly must reside in waters that contain at least one of the four other Poecilia. It has been determined that they have been asexually for 100,000-200,000 years with approximately 500,000 generations. They are rare in that asexual lineages typically go extinct after 10,000-100,000 generations. They are omnivores that feed on algae, plant matter and small invertebrates. In turn they are preyed upon by various pelagic and surface predatory fish as well as numerous birds.
The Amazon Molly is a straightforward identification with the exception of the females are similar to the Sailfin Molly, Poecilia latipinna (brown spots on the sides).
The Amazon Molly is found within the Atlantic Slope in the freshwater coastal system from southern Texas in the lower Rio Grande, south to northern Veracruz in the states of Hidalgo, Nuevo León, San Luis Potosí, and Tamaulipas.
From a conservation perspective the Amazon Molly is currently considered to be of Least Concern with stable, widely distributed populations. They have been introduced throughout the world from escapes, intentional releases from fish farms to control mosquito populations, and releases by aquarists raising havoc of native fishes and their environments. Long term they are threatened by human development of their native habitat.