Species Description: The sailfin molly, Poecilia latipinna, is one of three species in the IRL belonging to the family Poeciliidae. Members of this family are viviparous, giving birth to live young instead of spawning or laying eggs. These fishes are further characterized by: a single, spineless dorsal fin; a squared off or rounded caudal fin; and an anal fin in males modified into a copulatory organ, called a gonopodium (Robins & Ray 1986). Both sexes of P. latipinna have rows of dark spots along each scale row, but are otherwise dimorphic (Robins & Ray 1986). The dorsal fin in males is long and sail-like, with an orange edge, a series of black bars toward the outer half, and dark lines and spots near the base. The caudal fin is orange and blue with dark lines and spots, and the upper body is blue. Females lack bright coloration, most markings, and the elongated dorsal fin.
Potentially Misindentified Species: As mentioned above, two other poeciliids are found in the IRL: the mosquitofish, Gambusia affinis; and the mangrove gambusia, G. rhizophorae. Both species are much smaller than the sailfin molly, reaching a maximum length of 4 and 5 cm, respectively (Robins & Ray 1986).
The mosquitofish is silvery, with pigmented borders on the scales forming a dark diamond pattern. The body and caudal fin usually bear rows of small black spots, and a dark bar is present below the eye. The lining of the body cavity, or peritoneum, is black and visible through the abdomen.
The mangrove gambusia is similar to G. affinis, but lacks the dark bar below the eye and the spots on the caudal fin. Small but conspicuous black spots line the upper side, and the fins are yellowish in color.
A third species that may be mistaken for P. latipinna is the invasive guppy, P. reticulata (Ferriter et al. 2006), which most likely was introduced to Florida waters via the aquarium trade. The guppy reaches lengths of approximately 6 cm, with females larger than males. Males also have large, colorful caudal fins.
Regional Occurrence & Habitat Preference: The sailfin molly is native to the coastal waters of the Gulf of Mexico and the Atlantic Ocean, from southeast North Carolina to the Yucatan, including estuaries and freshwater tributaries (Burgess 1980, Meffe & Snelson 1989, Robins & Ray 1986). Individuals have been found in shallow marsh areas, and large populations inhabit areas were water flow has been altered (eg. mosquito impoundments) (Williams et al. 1998). Because of its wide environmental tolerances and popularity as an aquarium fish, P. latipinna has been introduced throughout the world (Courtenay & Meffe 1980) to locations such as: California, including the Salton Sea (Zedler 2001); and the cave and basin hotsprings of the Banff National Park in Alberta, Canada (Nelson 1983).
IRL Distribution: The sailfin molly is found throughout the IRL in many habitats. However, most populations are concentrated in mangroves and salt marshes, including closed and restored mosquito impoundments (Klassen 1998, Lin & Beal 1995).
Age, Size, Lifespan: The maximum age and lifespan of P. latipinna is unknown, and growth varies with food availability, environmental conditions and other factors. The maximum reported size of the sailfin molly is 12.5 cm (Robins & Ray 1986), although most specimens collected in the IRL are less than 6 cm (Klassen 1998).
Abundance: Sailfin mollies reportedly live in small shoals, or groups, comprised of 10-20 individuals of both sexes (Aspbury 2007). Abundance of P. latipinna throughout mosquito impoundments surveyed in the IRL exceeds 3,500 individuals (Klassen 1998), accounting for over 30% of the total catch in the impounded areas of St. Lucie County, Florida (Lin & Beal 1995).
Reproduction: Many studies have investigated the reproductive behaviors of P. latipinna, and several countries have successfully cultured the species for the aquarium industry (Ghosh et al. 2003, Ramachandran 2002).
Sex can be determined when individuals reach a length of about 1.6 to 1.8 cm (Snelson & Wetherington 1980). Populations are comprised of females, dominant males, and small "sneaky" males (Snelson 1982). Studies have shown that females prefer larger males when presented with several mates simultaneously (MacLaren & Rowland 2006). These larger males frequently engage in territorial courtship displays, and smaller males must "sneak" in to inseminate females without courtship in order to be reproductively competitive (Farr et al. 1986, Travis et al. 1990, Travis 1994, Travis & Woodward 1989).
Sperm production and expenditure also vary in mollies as methods of reducing competition between males (Aspbury 2007). In high-risk situations, more sperm is produced in all males, and smaller males expend more sperm during insemination. Female P. latipinna also have the ability to store sperm, allowing a single fertilized female to establish a new population (Courtenay & Meffe 1989).
In addition to conspecific reproduction, breeding between the sailfin molly and the shortfin molly, P. mexicana, produces the Amazon molly, P. formosa (Gabor & Aspbury 2008, Gabor & Ryan 2001). This hybrid species is unisexual (all female), and sperm is needed from one of the parent species to begin egg development, although inheritance is completely maternal (Gabor & Aspbury 2008). This process of reproduction is known as "gynogenesis". Male P. latipinna successfully reproduce with P. formosa, but tend to prefer copulation with conspecifics females, especially when they are larger (Gabor & Aspbury 2008).
Embryology: Embryological information for P. latipinna is sparse when compared to studies on reproductive behavior. Although they are considered livebearers, the degree of viviparity in sailfin mollies appears to vary with nutrient availability (Trexler 1985). When maternal females have access to abundant nutrient sources, they partition internal nutrition for their young throughout development, and are considered "truly viviparous" (Amoroso 1960). When nutrients are scarce, females expend energy at the beginning of development to produce a yolk that will sustain the embryos until birth, a process known as "ovoviviparity" (Scrimshaw 1945). Females brood several times throughout the year, producing batches of up to 140 fry (Zedler 2001) measuring about 8.7 mm each (Snelson 1982). Growth rates in female juveniles and adults usually exceed those in males.
Temperature: The sailfin molly resides mostly in warm coastal waters. However, this is a robust species that can withstand a wide range of water temperatures. The thermal tolerance of P. latipinna has been documented from approximately 6 to 40°C, and depends somewhat upon the temperature to which the individual was previously acclimated (Fisher & Schlupp 2009). As with all livebearers, the optimal temperatures for reproduction are reported to be between 22 and 26°C (Dawes 1991).
Salinity: The sailfin molly is one of only a few species of bony fishes that are considered to be truly euryhaline, inhabiting fresh to hypersaline waters (Nordlie et al. 1992, Zedler 2001). Populations have tolerated salinities up to 80 ppt, depending on the salinity to which the fish were previously acclimated (Nordlie et al. 1992). An even wider salinity range of 0 to 94.6 ppt has been documented in other studies (Kumaraguru Vasagam et al. 2007). However, captive breeding of P. latipinna is reportedly least successful in freshwater (eg. Kumaraguru Vasagam et al. 2005). Salt is typically added to molly tanks to induce breeding (Whitern 1983), and a salinity of 25 ppt yields faster growth and the most fry per clutch (Kumaraguru Vasagam et al. 2005).
Dissolved Oxygen: Sailfin mollies are often found in stagnant or low-flow areas. Studies have shown that individuals can become acclimated to hypoxic conditions, with dissolved oxygen concentrations as low as 1 mg per liter (Timmerman & Chapman 2004). The ability to tolerate hypoxic conditions may be due in part to the larger gill surface area found in natural populations that inhabit low oxygen waters.
Trophic Mode: The diet of P. latipinna is mostly herbivorous, containing large portions of algae and detritus (Zedler 2001). However, decaying animal tissue and microscopic benthic invertebrates are likely inadvertently consumed as well. Optimal growth in cultured juveniles is achieved through mixed diets of fish and soy bean meal, oysters and tube worms (Kumaraguru Vasagam et al. 2007).
Predators: Few predators are documented for this species, but individuals are likely preyed upon by larger fishes, wading birds and crabs.
Associated Species: No known obligate associations exist for P. latipinna. However, sailfin mollies are associated with several organisms common to mangroves, mosquito impoundments, seagrass beds and salt marshes.
Economic Importance: Three of the top 10 ornamentals imported into the US are poeciliids, and these species account for approximately 50% of the ornamental market in India (Mahapatra et al. 2000, Ramachandran 2002). As mentioned above, the sailfin molly is a popular ornamental fish traded globally by the aquarium industry, and much of the demand for P. latipinna throughout the world is satisfied by its captive culture in India and elsewhere (Ghosh et al. 2003, Ramachandran 2002). However, the invasion of these fish into new locations may have devastating effects (Williams et al. 1998) and economic consequences that overshadow their benefits to the aquarium trade.
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