Breeding Fish - Mollies (Poecilia)

Mollies are livebearers, what this means is that instead of laying eggs like many other types of fish, the eggs are fertilized inside the fish and a pregnant molly fish will release live fry (baby fish). There are a few common types of livebearers that are common in the home aquarium, these include, mollies, guppies, swordtails and platies.

Before you consider breeding your fish you should be aware that if you are successful you will need a lot of space in your tank for your new fry (if you intend to keep them). Female Mollies can release fry once a month for around three months and can release anything from a few fry to over a hundred each time so you have to be able to look after them, at least until they are old enough to be moved on or sold.

As far as tropical fish go, Mollies are extremely popular, given the right conditions they are easy to look after and an attractive addition to any aquarium. To breed them is really not a difficult task, in fact if you have a few mollies in your tank (as long as there is a male) and you let nature take its course you may well end up with many tiny fry in a short space of time. But most aquarium owners will at some stage consider breeding their fish.

Below you will find the specific's that will help you to successfully breed your molly fish and care for the fry.

Molly Fish Breeding Tips

Molly fish will breed without any help from you, as long as your tank is set up to their liking and you have at least one male and a couple of female mollies. It is usually best to have only one male and make sure that the females outnumber the male. For instance in my own tank I have one male molly and four females and this setup seems to work quite well for me.

Caring for Your Pregnant Molly

There are a few things you can do to help your pregnant molly fish, firstly the conditions need to be right for her to release her fry. Below are the conditions that should help her on her way.

  • Keep the temperature between 78 and 82 degrees F. If after a few days she hasn't released it and the temperature is at 78, you can try raising it by 2 degrees to see if it will make a difference but do not put it any higher than 82.
  • Feed her well, give her a mixed diet, flake food is fine but try and add frozen blood worms etc every other day.
  • Do regular water changes, in my opinion every other day is adequate, change 20% of her water every second day.
  • Keep her away from other fish, other fish, especially the male molly can stress a female that is close to releasing her babies. If she becomes too stressed she may not release them or she will release them too early.
  • You can add some aquarium salt to the water although I have not found this necessary in my aquarium.

As long as you do the above you should have little problems breeding mollies.   

Which Type of Mollies Can I Breed?

Molly fish are all the same species so any molly can breed with another despite the differencesBreeding Molly FishCredit: Alana R
in them, for instance any color molly fish can breed with another giving a wide variety of colorful fish. I have 6 molly fish in my tank currently and every one is distinguishable from the other by coloring and pattern. Likewise a pot bellied molly can breed with sailfin (Poecilia latipinna) molly and so on.

How to tell if your Molly fish is Male or Female

How to Tell the Difference Between Male and Female Molly Fish

Unlike some other fish, it is easy to tell the difference between livebearer's such as mollies and swordtail's. Female molly fish are usually plumper than the males but this alone is not a great indication. The best way to find out the sex of your molly is to look at the anal fin. On the female the fin is normal looking but the male molly has a different type of fin called a gonopodium whereas the female molly has a fan like anal fin.

You can see examples in Breeding Tropical Fish

Is my Fish Pregnant?

How to Tell if your Molly fish is Pregnant

More often than not, female mollies are pregnant if they have been in a tank with a male in the last 3 or 4 months or so. Molly fish are pretty easy to breed and because a female molly only needs a male around for short time to release fry every month for 3 or 4 months afterwards. In other words once she gets pregnant, she will not need another male for a couple of months at least and during that time she will give birth several times.

You can tell when she is pregnant by her belly swelling up, this actually can happen quite quickly and it normally takes 6 to 8 weeks for the first batch of fry to be released. Another way of telling is by looking for a gravid spot, but this is not always that reliable.

How Can I Tell When my Pregnant Fish is Ready to Release Fry?

This is not always so easy to tell and is learned from experience, you may notice a change in behavior in your fish, she may want to distance herself from other fish or might start eating more or less food than she normally would.

It can be hard to tell unless you know what to look for and each fish can act differently when the time comes. Even if you have been watching your fish carefully you may miss the event but because they release fry so often you should be able to begin to notice behavior changes for the next time she is ready.

My male molly with his fry!

Male Molly Fish and FryCredit: Alana R