Caresheet: Molly Fish | Poecilia Sphenops




Poecilia Sphenops

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Poecilia sphenops, also known as mollies, are one of the most popular aquarium fish species. These livebearers are available in many different colors and patterns and are sure to add a fun note to your aquarium. They make an easy breeding project and also offer a great opportunity to set up a brackish tank.

Keep reading for everything you need to know about molly fish and keeping mollies in your own aquarium!

Minimum tank size35″ (90cm)
Temperature71.5-82.5 °F/22-28 °C
dH10-25 °
Caresheet: Molly fish | Poecilia sphenops


Poecilia sphenops is commonly known as the shortfin molly (to set it apart from its sail-finned cousin) or just ‘molly’.

Many color varieties with different names exist and the scientific name isn’t fully agreed on, which does make things a little confusing at times.

Poecilia sphenops natural habitat

Molly fish are found in Central and South America, where their natural habitat ranges from Colombia to Mexico. They aren’t fussy about salinity and inhabit brackish, fresh and even marine waters.

Molly fish are also an invasive species in various countries.

Poecilia sphenops appearance

Poecilia Sphenops Molly Fish

Wild type mollies are mostly silverish with a little color on the fins. You won’t find many in the aquarium trade, though, as almost all mollies are hybrids mass-bred in captivity. Selective breeding has produced an endless variety of colors, fin shapes and even body shapes. Many of these are the result of crossing the short-finned Poecilia sphenops with Poecilia latipinna, also known as the sailfin molly.

The most popular molly color morph is the black molly, which is entirely black. Other color varieties include the dalmatian molly (silver and white speckles), gold dust molly (yellow/orange) and chocolate (brown). Body shape can vary as well. Lyretail mollies sport a typical lyre-shaped tail. Balloon molly fish have been selectively bred for an extremely round body shape but are not appreciated by most serious molly breeders, as they are essentially deformed.

Most mollies grow to a maximum size of around 4.5 inch (12cm) for the females and 3 inch (8cm) for the males.

Poecilia sphenops requirements

Mollies are one of the most popular aquarium fish species because they are pretty easy to keep and not too demanding. Unfortunately, though, many mollies die a premature death from being kept in unsuitable setups like bowls and tiny aquariums.

  • Tank size. Some sources recommend these relatively large and very active fish for aquariums as small as 5 gallons (19L). In realily, the species actually needs a much more spacious tank. To keep your mollies happy and healthy provide them with an aquarium of at least 35″ (90cm).
  • Group size. Don’t keep molly fish alone or in pairs: a harem consisting of one male and two females is the minimum number. More is always better, though, as they love plenty of company and look their best when kept in a larger group.
  • Water quality. Your molly tank should always be filtered, heated and fully cycled. Like most livebearers but unlike many other popular aquarium fish species mollies don’t appreciate soft, acidic water. Hard water with a pH of at least 7 is needed to keep them healthy.
  • Salt. Another interesting and highly debated point is salt. Most aquarists keep mollies in freshwater setups and have no idea their fish can actually thrive in brackish or even marine water. While fresh water should be fine as long as water quality is high many molly keepers swear their fish seem healthier with a bit of added salt. Luckily, a brackish aquarium isn’t difficult to set up at all. This article contains everything you need to know!
  • Decorations. Provide your mollies with plenty of hiding places in the form of plants, but be sure to also keep some open space so they can swim freely. Vallisneria is an easy plant that should work well for larger tanks and can handle the high pH mollies need.

Poecilia sphenops tankmates

Mollies are a very popular choice for community aquariums but unfortunately keeping them with other tropical fish isn’t always the best idea. They are very active and known to be a little nippy at times, which makes them a bad combination with very calm or long-finned fish.

Water quality is another point with mollies, because as discussed earlier because they need hard water and a high pH. Many other aquarium fish prefer more soft and acidic water. Although most of the commonly kept aquarium fish species are quite adaptable you’re best off avoiding the ones that specifically require these different water values.

Good tankmates for mollies include other livebearers like guppies, as these can also handle a high salinity and like harder water. Other than that, most sturdy fish that prefer or can at least handle similar water values should work. Cherry barbs (Puntius titteya) might make a good match in freshwater setups.

Poecilia sphenops diet

Like other livebearers, mollies are omnivores with a preference for plant matter. They especially love algae and, as a result, can often be seen “cleaning” leaves and glass by scraping off any algae they can find.

Feed a variety of foods to keep your mollies healthy. Herbivore pellets can be combined with frozen foods such as mosquito larvae and fresh blanched vegetables like spinach. You can also offer pretty much any other fish foods you’ve got lying around for extra variety. These livebearers are not picky at all and will gladly attack anything edible they come across.

Breeding Poecilia sphenops

One of the characteristics mollies are best known for is their quick reproduction. They are livebearers, which means females give birth to over 100 relatively large live young at a time.

To breed your mollies, make sure you have 2 females for every male. Fill the tank with plenty of fine-leaved plants like Java moss to help the fish fill safe and provide the fry with some cover. Adult female mollies should always constantly be pregnant and as long as your water values are in order fry should start to appear soon enough.

Keep in mind that the adults do eat their young, so unless the tank is very heavily planted it’s a good idea to move them to a separate grow-out tank or breeder box. Use powdered foods to feed the young mollies until they are large enough to go back into the main tank and forage alongside the adults.

Never place the female in a breeding box. The stress can easily cause her to release the young prematurely or even miscarry! Just make the main aquarium a suitable place for a pregnant female to inhabit, with plenty of cover and no overly active tankmates.

If you have any more questions about molly fish care or want to share your own experiences with these lively fish, don’t hesitate to leave a comment below!

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2 thoughts on “Caresheet: Molly Fish | Poecilia Sphenops”

  1. We started with a group of mollies and some rainbow tetras along with aqua frogs. After some time we were down to one Molly who ate aggressively, one rainbow, a couple albino cats eating algae and about 6 little froggies.
    Today i found one mini baby molly, orange like its mama! Did she get started with some other mollies when they were together and hold that sperm for when she was mature? Will she continue birthing?


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