Mollies and Guppies, Livebearers of the Genus Poecilia
Mollies and Guppies are some of the most popular fish in for freshwater fishkeeping and many of the species are Native to North America. Though some of the fancy variations sold are of questionable health, the wild (and wild-type) Mollies are hardy and supremely adaptable. Coupled with their attractive colorations, it’s not hard to see why these fish have made such an impact on the pet fish trade!
Species
The genus Poecilia is one of the 41 genera of the family Poeciliidae (Live-bearing Tooth-Carps), containing 40 species. Of these, 14 are native to North America (5 in the USA, and all 14 in Mexico):
- Poecilia butleri (Pacific Molly)
- Poecilia catemaconis (Catemaco Molly)
- Poecilia chica (Dwarf Molly)
- Poecilia formosa (Amazon Molly)
- Poecilia latipinna (Sailfin Molly)
- Poecilia latipunctata (Broadspotted Molly)
- Poecilia maylandi (Balsas Molly)
- Poecilia mexicana (Shortfin Molly) [pictured]
- Poecilia orri (Mangrove Molly)
- Poecilia petenensis (Peten Molly)
- Poecilia reticulata (Guppy)
- Poecilia sphenops (Molly)
- Poecilia sulphuraria (Sulphur Molly)
- Poecilia velifera (Giant Sailfin Molly)
The most commonly sold varieties are Guppies and Mollies (P. sphenops) and they are generally available in all freshwater fish stores. Less commonly, the Sailfin Molly is sold and even more uncommon is the Giant Sailfin Molly. Other species are not often sold outside of auctions or specialty clubs/stores.
Conservation Status
The Amazon and Sailfin Molly populations are considered stable and of Least Concern by the IUCN. The Broadspotted and Sulphur Molly are both Critically Endangered, and the other 10 species have not been evaluated.
Distribution
For the most part, these Mollies are all widely distributed from the northern part of Mexico to the southern border, with several species also being found in Central America.
The Shortfin Molly, Sailfin Molly, and Guppy can all be found from north Carolina and south through to the lower part of Florida and have some populations in Texas. The Amazon Molly and Broadspotted Molly can both be found to the extreme southern part of Texas, though there are also introduced populations of Amazon Mollies in San Antonio and San Marcos, Texas.
Description
Mollies are mostly small-sized fish. Some of the smaller species (the Dwarf and Sulphur Mollies, the Guppy) only reach 2 inches, and the majority of the other species top out somewhere between 3-4 inches. Even though the Sailfin and Giant Sailfin Mollies have a maximum length of about 6 inches, it is much more common to see them in the 3-4 inch range as adults. Females are commonly larger than the males.
As far as aggression and territoriality go, mollies are generally pretty mild fish, given sufficient space. Male mollies can be pushy towards smaller males of the same species or similar species (even including other genera like Xiphophorus) and thus it is not wise to keep multiple males in small tanks. Also, to avoid males endless pestering females, a ratio of 1 male to 2 or 3 females will spread around the male’s attention. Groups of females are normally well behaved, though sometimes bickering does occur. Neither sex are normally pushy towards dissimilar fish. My experience is that Mollies are likely to pick at the slime layer of larger, slower fish. I personally try not mixing them together for that reason.
Mollies do seem to appreciate being kept in tanks with live plants, both for the comfort of something to hide behind and nibbling on the microscopic animals and algae growing on the leaves. Molly fry also seem to like swimming near floating plants, giving them a better chance to survive being eaten.
Feeding
Proper nutrition depends on species. The majority of mollies are omnivorous, with a focus on plant matter over animal matter. For these fish, an algae-based flake or pellet food would make the best staple, combined with the additional offering of pieces of vegetables (like blanched cucumber) and frozen meaty foods like brine shrimp. Guppies are an exception, focusing more on animal foods than plant foods. Flake food with a higher protein content is better, with more frozen animal matter supplemented than the other species.
All mollies should be introduced to established tanks only, with some algae to graze on (yes, even Guppies do better this way). The addition of plants to low brackish or freshwater systems is highly recommended and will provide leafy material that will be nibbled on.
Water Quality
If you have got rock hard water, you have happy mollies. Anything more than moderately hard (upwards of 15 dH) and alkaline (pH 7.5-8.5) is perfect for these fish. The water should also be warm, anywhere between 75 and the low 80’s F should be fine.
Mollies are largely intolerant of nitrites and nitrates. In freshwater, nitrite spikes are particularly dangerous to these fish and nitrates should be as low as feasible; should be kept below 10 mg/l and never above 20 mg/l. Salt lowers the toxicity of nitrites and nitrates, though, and mollies kept in brackish or saltwater tanks do not appear to be nearly as sensitive in terms of water quality.
Brackish Suitability
The genus Poecilia is very well known for having members which are freshwater but highly adaptable to brackish conditions. All of the members of this genus can be adapted to at least low end brackish conditions and many (including the Molly and Guppy, but also the Sailfin, Giant Sailfin, and Pacific Molly, among others) can even be kept in fully marine conditions.
Whether or not mollies should be kept in brackish conditions is debatable. On the one hand, mollies appreciate the rock hard water brought on by the addition of marine salt, salt lowers the toxicity of fish wastes, it fights freshwater diseases, and mollies kept in freshwater seem to be prone to more health concerns (including neurological) than those kept in brackish conditions. On the other hand, many mollies come from areas in the wild which are naturally freshwater, and a suitably sized tank with extremely hard water and frequent water changes is an option.
As many (perhaps most) problems with mollies stem from environmental causes, it is highly recommended to keep mollies in at least low end brackish conditions. Somewhere around 1.002 to 1.003 is good and will allow for cohabitation with salt-tolerant freshwater fish and plants.
Tank Size
For the smaller species of mollies (the Dwarf Molly and the Guppy) a tank of about 15 gallons will work fine for a small group. Though a single male will do fine in a 10 gallon species only tank, multiple males may fight and should not be kept in small quarters. Females are likewise a bit too big and may feel confined in such small quarters.
The other species of mollies will all do fine in groups in a 30 gallon tank. Larger Giant Sailfin Molly specimens may do better in moderate sized groups in a 40 or 55 gallon tank.
Breeding
Breeding mollies is extremely easy for the beginner aquarist, and is as simple as putting males and females together and feeding them high quality foods. Females can give birth every 3-6 weeks, depending on species, when kept with males. Even when separated from males, the females can store sperm for months and still reproduce. Only females which have never been kept with males (not typically an option for wild caught or store purchased fish) won’t produce fry. Fry can be raised in a separate tank (of at least 10 gallons) and will accept powdered food or finely crushed flake food from day one.
The Amazon Molly is a special case and reproduces gynogenetically. Sperm is accepted from other species in the genera but is not used during conception and all Amazon Mollies are genetically the same as the mother. In fact, all Amazon Mollies are females.
All mollies can interbreed and thus should be kept separately (except in the case of the Amazon Molly, if wishing to breed). Hybridization has been noted as particularly devastating for some species of molly, including the Endler’s Livebearer which readily hybridizes with Guppies and is at risk of extinction in the wild due to this if it isn’t extinct already (though pollution in their native waterways is also a concern).
Final Thoughts
Attractive, easy going, and hardy; mollies make wonderful tank inhabitants and pleasant community residents. Assuming you have the right sort of tank which can handle the low addition of salt, these fish are very desirable choices for aquarium life.
Sources
Fish Identification, Fishbase
First record and establishment of an exotic molly (Poecilia butleri) in the Baja California Peninsula, Mexico, Deivis S. Palacios-Salgado, Arturo Ramirez-Valdex, Gorgonio Ruizcampos
Fantastic Four Livebearers, Neale Monks
Livebearing Fishes for Aquariums and Not, Bob Fenner
(Image Source: Me!)
