Mollienesia

Sailfin molly

The sailfin molly, Poecilia latipinna, is a species of fish, of the genus Poecilia. They inhabit fresh, brackish, and coastal waters from North Carolina to Texas and the Yucatan Peninsula of Mexico.

Taxonomy

The sailfin molly was originally described in 1821 as Mollienesia latipinna by the naturalist Charles Alexandre Lesueur. Lesueur based his description upon specimens from freshwater ponds in the vicinity of New Orleans, Louisiana. However, Lesueur described other collections of the sailfin molly as Mollienesia multilineata in 1821, the same year in which he described M. latipinna. This conflict created confusion and eventually necessitated a ruling by the International Commission on Zoological Nomenclature (ICZN). In 1959, the ICZN placed precedence on the name Mollienesia latipinna Lesueur 1821. In a landmark definitive work on Poeciliid fishes, Donn Rosen and Reeve Bailey (1959) noted the priority of Poecilia by Marcus Elieser Bloch and Johann Gottlob Schneider (1801) with regards to Mollienesia by Lesueur (1821), thereby relegating Mollienesia to the synonymy of Poecilia.

Common names

Sailfin molly (English), Breitflossenkärpfling (German), Seilfinnemolly (Norwegian), Zeilvinkarper Dutch, Molinezja szerokopłetwa (Polish), bubuntis (Tagalog), and molliénésie á voilure or simply "molly voile" (French).

There is some confusion with the Yucatan molly, P. velifera. While most names that contain a sail element refer to the present species, the German "Segelkärpfling", the Latin velifera and possibly others are used for the Yucatan molly. The French terms are used for both species indiscriminately.

Geographical distribution

The sailfin molly is found in fresh, brackish, and coastal salt water in coastal lowland habitats from North Carolina to Texas and the Yucatan Peninsula of Mexico. Preferring marshes, lowland streams, swamps, and estuaries, the sailfin molly is very common in peninsular Florida. Non-indigenous populations are established in New Zealand, in the western U.S. and in Hawaii. Sailfin mollies introduced to California have caused a decline in populations of the Federally protected and endangered Desert Pupfish (Cyprinodon macularius).

Habitat

Sailfin mollies are most commonly observed as the shallow surface waters along the edges of marshes, lowland streams, ponds, swamps, estuaries and even ephemeral water bodies such as roadside ditches. Small to large aggregations of the species are most commonly found under floating vegetation or near structures in the water, minimizing their chances of being observed by potential predators.

The sailfin molly is a tolerant species. for exploiting the thin film of oxygen rich surface water with their upturned mouths, sailfin mollies are able to survive oxygen depleted habitats. A euryhaline species, the sailfin molly may be found in a variety of saline environments tolerating salinities as high as 87 ppt and will breed in brackish waters.

Adults thrive best in isolated pools or organically enriched waterways where few other fish occur (Minckley 1973).

Biology

Distinctive features

The body of the sailfin molly is essentially oblong. The head is small and dorsally flattened, with a small, upturned mouth. The caudal peduncle is broad and the caudal fin is large, rounded, and sometimes tipped with black. The pelvic fins originate at a point anterior to the dorsal fin. In mature males the dorsal fin is greatly enlarged and colourful (it is this feature that gives the species its common name) and the caudal fin is similarly colourful, these conspicuous secondary sexual features play a role in female mate choices. Females tend to be larger and more plainly coloured, a difference characteristic to the Poeciliidae. (See: Sexual selection)

It is a smaller fish than the Yucatan molly, though that species often does not grow to full length if bred in an aquarium. The dorsal fins are the most distinctive character: Those of the sailfin molly have less than 15 fin rays, counting where the fin meets the back, whereas the Yucatan molly has 18-19 (intermediate numbers may indicate hybrids which should be avoided). If the males spread their dorsal fin in display, in this species it forms a trapezoid with the posterior edge being shortest. The height of the dorsal fin, measured at the posterior edge, is a bit less than the height of the tail

Colouration

The body is generally light grey, although breeding males may be greenish-blue. Several rows of spots occur along the sides, back, and dorsal fin. Often these spots blend together forming stripes. Aquarists have developed many colour variations in this species, (variation occurs naturally in the wild) with melanistic, leucistic, albino, and speckled forms known.

Sailfin and black mollies

There exists an entirely melanistic form called the Midnight molly, or, nondescriptly, "Black molly". The latter originally refers to melanistic breeds of Poecilia sphenops. Midnight mollies actually originated from hybrids between that and the present species.

As hybridization, like in most Poecilia, is easy between these two species and due to the more spectacular appearance of P. latipinna, such Sailfin-Black molly hybrids, with males' conspicuous, large, yellow-rimmed dorsal fin are often seen. Due to genomic recombination, F1 hybrids often display novel and bizarre fin shapes. This can include a grotesquely elongated gonopodium in males; such hybrids are usually unable to breed. Otherwise, hybrids can be bred among themselves, or with higher rate of success with their parent species. They often have a somewhat decreased lifespan, but not as much (in healthy fish) as the deformed "balloon" molly breeds of P. sphenops. Like the sailfin molly, they require a bit more attention of the fishkeeper than the extremely hardy "true" black mollies.

Size, age, and growth

The natural lifespan of sailfin mollies, is short, particularly in the case of the males, which may live less than one year after achieving sexual maturity. Depending upon environmental conditions sailfin mollies may become reproductive in less than a year. Sailfin mollies are small fish. At one year of age males typically range in size from 15-51 mm SL while mature females are likely to be approximately 19-53 mm SL. The sizes of adult males is directly correlated with population density. The greater the population, the smaller the average size of males. The maximum recorded size for this species is 150 mm TL.

Food habits

Sailfin mollies feed primarily upon algae and other plant materials, although they will consume a number of aquatic invertebrates including the larvae of mosquitoes.

Reproduction

Fertilization is internal and is accomplished by means of highly modified fin elements within the anal fin of males that form a structure known as the gonopodium. Sailfin mollies produce broods of 10-140 live young, depending upon maturity and size, and females may store sperm long after the demise of their relatively short-lived mates. The gestation period for this species is approximately 3-4 weeks, depending upon temperature, and a single female may give birth on multiple occasions throughout the year. Although sex ratios of the broods are balanced, adult populations tend to be largely female as males appear to suffer higher rates of mortality due to a greater susceptibility to predators and disease as a consequence of their brighter colours and a life devoted to frenzied breeding. There is no parental care exhibited by this species.

Predators

Sailfin mollies are members of the lower end of the food chain. As such they are prey for various animals including aquatic insects, other fishes, reptiles and amphibians, birds and mammals. Specific examples include: giant water bugs (Belostomatidae), largemouth bass (Micropterus salmoides), American alligator (Alligator mississippiensis), bullfrog (Rana catesbeiana), snowy egret (Egretta thula), and racoon (Procyon lotor).

Parasites

The trematode, Saccocoelioides sogandaresi is a known parasite of the sailfin molly.

Importance to humans

The sailfin molly, in its many colour varieties is of considerable interest and value to aquarists and many artificially selected varieties are produced and sold in pet shops. Wild type sail fin mollies are also bred as feeder fish for larger carnivorous fish. Naturally occurring populations of sailfin mollies help to control mosquito populations by feeding on the larvae and pupae of these pests. As noted in "Distribution" above, they may not be suitable as a biological control agent in many cases as they can easily become an invasive species, even a pest themselves.