Guide to Breeding Mollies

Here Come The Fry Babies!

Mollies are live-bearing fish. Live-bearing fish do not lay eggs but give birth to live tiny little fish babies. These babies are known as Fry.

Before allowing your Mollies to mate, you will need to set up a separate tank. This tank will house the fry until they are grown enough to introduce into the main tank with the other fish.

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Female or Male?

It is very simple to see which are males or females in Mollies.

  • Male: anal fin is shaped like a stick
  • Female: anal fin is shaped like a fan

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The Nursery Tank

Your nursery tank will act as a temporary home for the fry until they are grown enough to be placed into the tank with your other mollies. Adult Mollies eat small fry, so it’s necessary to keep them separated until the fry is bigger.

Guide to setting up a nursery tank:

You will need to purchase items for your nursery tank.

  • 15-30 gallon tank (size is dependent upon how many fry you have) OR use a simple 2-way breeder box that goes directly into your existing tank. If you do use a 2-way breeder box, you will not need any of the below items.
  • Filter System
  • Plants and ornaments for fry to hide in
  • Gravel for substrate
  • Food for the fry
  • Water conditioner (if you do not have already)
  • Heater for tank
  • Thermometer for the tank to monitor water temperature
  • Lighting for the tank

Set up your nursery tank

  • Thoroughly rinse the inside of the tank with plain water. Use a paper towel to dry.
  • Rinse the gravel, drain and allow to dry.
  • Fill your aquarium halfway with room temperature water.
  • Add your artificial plants and accessories.
  • Add the remaining water filling the tank up to 1” of the top.
  • Treat your aquarium water with the water conditioner / dechlorinator.
  • Set up the filtration system and turn on.
  • Allow nursery tank to operate 3 days before adding fry to it.

If you are using a 2-way breeder box, insert it into the main fish tank and allow to remain there for a few days to allow the other fish to become accustomed to it.

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2-Way Breeder Box

Ready to Mate Fish

  1. Fish mate by the male positioning himself below the female. Once they have mated, the fry will be born 3-5 weeks after. 
  1. When the mother is close to giving birth, move her into the nursery tank (2-way breeder box or separate nursery tank.)
  1. Once the fry are born, immediately move the mother back into the main tank. If you allow her to stay with the fry, she will eat the fry.
  1. Once a month, introduce the mother under supervision into the nursery tank to be around her fry and then return her back to the main tank.

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Feeding the Fry

Fry can be fed the same food you give to your adult Mollies. However, you will need to ground up the fish food before feeding to the fry. You can also grind up bloodworms, and brine shrimp and give to the fry.

Separating the Fry

Once you know the sex of your fry, steps need to be taken to make sure they do not mate. Separate the females from the males just before the fry reaches eight weeks old (sexual maturity.)

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Starting a new tank

Once you have separated the male fry from the female fry, you will need to calculate 1 male to every 2 females. You may be required to set up more new tanks to accommodate new fry as they mature.

Remember not to overcrowd your tank!

  • 5-gallon tank = 1 Molly
  • 10-gallon tank = 2 Mollies
  • 20-gallon tank = 3 Mollies

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Enjoying the Show

You are now equipped with enough information to successfully maintain a healthy tank and perhaps make a little money selling your fry.

Now it’s time to sit back and enjoy the hard work and effort placed into starting your Mollies!

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