Molly Fish: A Guide to Care, Breeding, Diet & Behavior

Molly fish has been a favorite among aquarists and is a freshwater fishkeeping staple. These fish are well-known for their low-maintenance needs and the large variety of different species.

In this guide, you will discover everything you need to know about molly fish, how to care for them, set up their tank, and breeding tips.

Molly Fish Overview

If you’re wondering where you would find molly fish in the wild, you will need to travel down to the United States’ southern regions, extending into the Yucatan peninsula in Mexico. Their natural habitat comprises freshwater environments, while occasionally, they venture into brackish estuaries. Mollies can acclimate to full-strength seawater for a short period, although it is not their natural environment.

The Molly’s genus, Mollienesia, has been reclassified as Poecilia, and it is now believed to be in the same genus as the guppy. Researchers have seen that the guppy will interbreed with the Molly in certain circumstances, and their close genetic link has been established.

Molly fish have, on average, a three- to five-year lifespan, depending on the type you buy. The level of care you provide will have a big impact on how long they live. Despite their resilience, mollies are prone to disease in an unclean environment.


There are roughly 39 different species of molly fish. A few are likely not available from your local pet store, but you can find where to find them with some research. Adult mollies can reach up to 5.5 inches in size once they reach adulthood.

Various species

Because of interbreeding between the various molly species, there are molly fish with different colors and fin shapes. Here are a couple of the more well-known ones.

  • Sailfin Mollies: With the standard body shape, sailfin mollies have a taller dorsal fin that runs along to the base of the tailfin. Sailfin mollies can also be found in various colors, including black.
  • Black Mollies: These fish are exactly as their name suggests – they’re entirely black! A few in this species may have splashes of color, such as orange or yellow fins.
  • Lyretail Mollies: The lyretail molly derives its name from the lyre, a musical instrument. The tail fins are spiked at the top and bottom, resembling a lyre.
  • Balloon Mollies: Balloon mollies come in various colors and get their name from their bellies. The belly has a round and puffy look even when not pregnant.
  • Dalmation Mollies: Dalmation mollies are popular and can be found in most fish stores. With a base white color, they are covered in specks of black across their bodies, looking similar to a Dalmation dog.
  • Gold Doubloon Mollies: The front half of the Gold Doubloon Molly is bright yellow, while the lower half is covered in black.

How to identify gender

Male molly fish

The sailfin is only found on males, and it can grow up to 6 inches in length in the wild.

Female molly fish

Molly fish are livebearers, meaning they carry eggs inside their bodies and give birth to free-swimming fry. Female molly fish have a regular-shaped anal fin, and a dark region inside her body, known as the gravid spot, appears at its base. Although it is similar to the womb, the egg is not linked to the mother’s body like mammals and is not fed directly by her.

Each egg has an embryo and is well-supplied with nutrients from the mother’s system, which the developing embryo consumes throughout its life. According to research, this species does not show parental care.


Molly fish are socially peaceful by nature, and because they are shoaling fish, they need to be amongst other fish and get along well with others. If you choose to keep molly fish, make sure you have a minimum of four fish, and if possible, you can keep more.

These fish love to group up, explore the tank and swim as a single unit. After that, they’ll go their separate ways.

If you keep males in the tank, you will likely see some aggression as they harass the females. However, there must be favorable breeding conditions for this to worsen. The male aggression isn’t violent, but it does cause the females stress.

You can prevent male aggression by keeping more females in the tank to outnumber the male molly fish.

Molly fish get along well with other fish species, so you can create a multi-species tank. You only need to do some research and choose peaceful fish species. It’s crucial you avoid fish that display aggressiveness, larger fish that will eat your fish, and fish similar in size to mollies.

The following fish species are excellent choices for sharing a tank with molly fish:

  • Platies
  • Cherry Barb
  • Rosy Barb
  • Yoyo Loach
  • Zebra Loach
  • Celestial Pearl Danio
  • Swordtail Fish
  • Dwarf Gourami
  • Cory Catfish
  • Bristlenose Pleco
  • Harlequin Rasbora
  • Several types of Tetras
  • Snails
  • Freshwater Aquarium Shrimp

Nutrition and Diet

Molly fish are mainly plant-eaters and mostly eat plants and algae. When taking care of mollies, feed them plenty of spirulina and blanched vegetables like finely chopped boiled spinach, zucchini, and lettuce to keep them healthy. You can also let them snack on the algae growth in the aquarium.

Mollies also enjoy the occasional high-protein snack, such as daphnia, frozen bloodworms, and brine shrimp. Live meals provide stimulation during feeding time, in addition to their nutritional benefits, so try to incorporate them into your fish’s diet regularly.

If you prefer a simpler diet for your molly fish, you can purchase pellets and dry commercial flakes from your local fish store. When choosing a brand, ensure that the products’ ingredients are nutritionally balanced.

Molly fish Care Instructions

Molly fish Care

Caring for molly fish is easy and doesnt require much work, making them perfect for first-time fish owners.

Tank Setup

The first thing you need to do is get your tank set up. The amount of fish you want to raise and the type of species will determine the tank size.

If you have a molly fish that’s 4.5″ (11.43 cm), you will need a 10-gallon tank. However, if you want to have many molly fish together, then a 20-gallon tank will ensure your fish thrive and grow well. Be sure you don’t overcrowd your tank with too many fish, as it will lead to fighting amongst the various breeds.

When it comes to Sailfin Mollies, you will need a tank of at least 30-gallons for the fish to live.

Molly fish love bright light in their tank as they’re diurnal-active species (active during the day). Ensure there’s a good supply of light on the tank’s ceiling, which will also aid the growth of the tank’s freshwater plants.

Your tank should be adorned with natural décor that replicates their natural environment in the wild. So add many plants and ornaments where your mollies can hide when they want shelter.

Add sand or gravel substrate to the bottom of your tank. The substrate will serve as an anchor for the live plants. Use tall plants such as Java fern and Anubias, and make sure you position them in such a way there’s still open space for the fish to swim.

Décor that can be added includes driftwood, small rocks, and caves to provide additional shelter. They will also develop algae which your fish can eat.

Water conditions

Mollies are adaptable fish and like slow-moving and shallow water. Therefore, you don’t need an artificial current and a water pump for the tank. Water should be clean and germ-free.

The water requirements vary by species, but here are some good starting points for most mollies.

  • pH levels: 7.5 – 8.5
  • Water temperature: 72 degrees F to 78 degrees F. Some species require temperatures as high as 80 degrees F
  • Water hardness: 20 – 30 dKH

To ensure your tank’s water is up to the standard requirements, it’s recommended you get an accurate water test kit to test the water regularly.

Because mollies produce a lot of waste, you will need a good filtration system. Ammonia and nitrate levels can quickly be raised to dangerous levels by a small group. Select a strong filter capable of holding a large amount of biomedia. Additional sponge filters, whether internal or exterior, are also beneficial.

If you have money to spend, consider purchasing a canister filter. If you have a smaller budget, you can get an affordable, high-quality filter that hangs on the tank.

Some molly species are more vulnerable to poor water conditions than others, resulting in a significantly shorter lifespan. It’s important you learn as much about the species you own and provide the best care possible.