Freshwater fish, Information, Species

Mollie: Complete Species Overview

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by Jason Matthews



Most aquarists will have mollies in their fish tank. This is because this fish species has low-maintenance needs, and there are many multiple mollie species to choose from. They easily adapt to most environments, making them a perfect addition to your tank.

However, like all other fish species, you need to properly care for mollies for them to stay healthy. This article provides all the tips you need to know about caring for molly fish, from diet and breeding to tank conditions. Read on!


Scientific Name: Poecilia sphenops

Common Name: Molly fish, molly, common molly, short-finned molly, sailfin molly

Life Expectancy: 5 years

Adult Size: 5.5 inches


Primary DietOmnivore
Beginner friendlyYes
Tank preferenceMid-dweller
Water temperature72-78F
Water pH7.5 – 8.5
Water hardness15-30 dGH
Tank sizemin. 10 gallons

Fun Fact

As you look for mollies to add to your aquarium, you’ll come across different types of mollies. Mollies are part of the Poecilia genus; therefore, apart from the guppy and Endler’s livebearer, every fish species in this genus is a molly.


Mollies are commonly found in Central America, Mexico, and the southern part of the United States. Most of them thrive in freshwater habitats; however, some can be found in saline environments. Just like guppies, mollies can acclimatize to shallow marine environments like harbors.


Mollie fish
[Image Credit: Eldergeek, Pixabay]

While there are multiple molly fish varieties, most have a similar body style and shape. Mollies have flattened bodies, triangular-shaped heads, and wide mid-sections. Their bodies taper down towards the snout and the tail fin.

Over the years, mollies have been interbred to develop different varieties. Here are the common ones you’ll come across in the aquarium trade.

  • Sailfin mollies: They have a standard body shape, light grey in color with dark spots. The dorsal fin is taller and extends to the base of the tailfin.
  • Black mollies: This is the most common type of molly. They have all-black bodies and splashes of orange or yellow on the fins.
  • Lyretail mollies: They have a beautiful tailfin that is fan-shaped. However, you’ll notice lengthy rays at the top and bottom.
  • Balloon mollies: These mollies get their name from their short, rounded bodies that look like inflated balloons. They come in different colors, including orange, black, yellow, and silver.
  • Dalmatian mollies: They look like Dalmatian dog breeds with their shiny and rounded fins. The base color is white with specks of black.
  • Gold Doubloon mollies: The front half of the body has bright yellow colors, while the lower part is pure black.


You can differentiate between males and females because only males have a sail fin and grow up to 6 inches. Additionally, males have a pointy caudal fin, while the anal fin in females is fanned and broad. Furthermore, most females have a visible gravid spot which they use to hold their young ones during pregnancy.

Average Size

Adult mollies grow to about 5.5 inches. While males are skinnier, females have rounder abdomens. This length makes it possible to stock mollies in a reasonably small fish tank.


Generally, mollies are a peaceful fish species that get along with others. They are shoaling fish, so they need to stay with other fish varieties to be comfortable. However, they can show some aggressive behaviors when triggered. Some of the common triggers are a crowded tank or aggressive tankmates.

Additionally, you’ll notice aggressive behaviors when you stock males. They tend to harass females, and the behaviors become worse if they want to breed. To reduce these tendencies, ensure that the females are more than the males.


Since they are mostly peaceful, mollies will get along with most fish species, especially if you have a community tank. However, the tankmates must be friendly and of the same size to avoid any issues. Since they are a schooling species, you can keep them in groups of four in one tank.

Some ideal tankmates for mollies include danios, guppies, platys, tetras, angelfish, swordtails, dwarf gouramis, rosy barbs, cory catfish, and some cichlids. Additionally, they thrive well with other aquarium tankmates like snails and shrimp.

Tank Size and Conditions

It’s easy to create the right tank conditions for molly fish because they are hardy. They live in shallow water surfaces and environments with loose vegetation in their natural habitat.

Therefore, you should create similar conditions in your fish tank. The minimum tank size is 10 gallons, and the pH should be between 6.7 to 8.5.

Your tank should have plenty of plants and places for shelter. Add gravel or sand substrate at the bottom of the tank because mollies don’t spend much time at the bottom.

As you add plants, position them along the tank’s perimeter to provide swimming space for the mollies. You should also add decorations such as rocks and driftwood.


Mollies mostly consume plant-based foods. Therefore, they feed on algae as a staple food. You can add growing algae to your tank to provide this food source. You can also supplement this with lettuce, spinach, and zucchini.  Additionally, feed your mollies live or frozen foods like brine shrimp and bloodworms.


Black and gold mollie fish
[Image Credit: Gita, Pixabay]

In captivity, mollies are easy to breed. Since they are livebearers, they retain the eggs in the body and give birth to live fry.

To ensure the fry survives, breed the mollies in a controlled environment. You can use a separate breeding tank with warmer temperatures. As you choose breeding mates, keep in mind that females prefer mating with the largest males.

Once the male fertilizes the eggs, the female will grow the fry for about 35 to 45 days. They can give birth to as many as 100 babies at a time.


If you are looking for a fish species to start your journey as an aquarist, mollies are an excellent option. They are colorful, peaceful, and easy to breed, making them ideal for both beginners and veterans.

Featured Image: Juan Carlos Palau Díaz, Pixabay


Jason Matthews

My name is Jason Matthews, and welcome to my website. When other kids were bragging about how their dog could sit and roll over, I was bragging about my latest Betta Fish and the cool sea castle I just added to his aquarium. 

Jason aquariume

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