15 Fun & Interesting Facts about Molly Fish

Molly fish are one of the most widely kept freshwater fish in the aquarium hobby.

They’re a community-friendly, beginner-friendly fish species that is widely available and affordable.

They showcase a lot of variety in terms of color and fin type. They’re an easy to care for fish that’s adaptable and hardy.


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If you’re curious about the molly fish and you’re considering keeping them, I put together a list of the most interesting facts about mollies:

1. They can survive in brackish water

Although some molly fish breeds can be found to be living in brackish waters, most mollies do just fine in freshwater, and they don’t actually rely on salty water for survival.

In fact, for most mollies salt is not a keeping requirement, and can only tolerate brackish water without it actually being a requirement.

Under no circumstances should you add salt to an aquarium, where other fish species are housed along with mollies as other freshwater fish species don’t tolerate salty water.

Same goes for planted aquariums too, since freshwater aquarium plants don’t tolerate salinity.

2. They’re a hardy fish species

Unlike other fish that are highly sensitive even to small changes in water quality, hardy fish like mollies are more forgiving when it comes to water parameters.

Although high toxin levels are harmful for them too, they’re better at handling small changes in water chemistry.

Sudden changes in temperatures or sudden spikes of toxins are not well tolerated.

3. They’re easy to raise

Since mollies don’t require expert care like sensitive fish species do, mollies can be raised by beginner aquarists as well.

Mollies are recommended starter fish for those taking up the hobby for the first time.

4. They’re livebearers

Molly fish don’t lay eggs, instead they give birth to live fry.

Fertilization of the eggs occurs inside the female fish that will only release the eggs once the eggs are hatched.

The resulting fry are able to swim and take their first bites within a couple of hours from birth.

Fry aren’t difficult to raise, and you can do it yourself, just be sure to meet their water requirements and feeding requirements (they can eat only small foods that fit their mouths because of their small size).

5. They reproduce fast

Molly fish breed vary rapidly. If you have male and female mollies in the same tank, you better believe it that they’ll reproduce.

The female molly can store the sperm for months and continue to produce fry multiple times from a single fertilization.

Keep a single male for every 3 females, so that females don’t become stressed out by the constant pursuit of males.

6. They produce a lot of fry

Larger mollies can release a hundred or so molly babies, therefore, they not only breed often, but they also produce a lot of fry.

7. They don’t raise their fry

Many fish will eat their own fry and mollies are no exception.

To prevent them from doing this, you’ll need to set up a breeding trap in their aquarium or set up a separate breeding tank, and then remove the female once she drops the fry.

8. They’re community-friendly fish

Molly fish are suitable for community aquariums if you house them together with other peaceful fish.

Since they’re mild fin-nippers, mollies should not be housed with fish that have long fins.

You should avoid housing them with aggressive species or large predatory fish as well as small fish that they might mistake for food.

Some fish compatible with mollies include guppies, platies, swordtails, gourami fish, danios, endlers, etc.

9. They’re omnivores

Molly fish thrive on a mixed diet that includes meat and plant matter.

For healthy development, they require both, so make sure to offer them flakes with a high proportion of plant matter, live and frozen or freeze-dried foods (brine shrimp, daphnia, blood worms, etc.).

You can soft-boil vegetables for them and feed them small portions.

10. They have a big appetite

Molly fish are ferocious eaters since they’re active fish.

Unfortunately, they’ll eat continuously and don’t know when to stop. Therefore, you must be careful not to overfeed them and offer them portions they can eat in 3-5 minutes.

11. They don’t live that long

Molly fish have an average lifespan of 3-5 years, depending on whether they are kept in captivity or not.

In the wild, they can live longer, however, you can prolong molly fish longevity if you offer them the right aquarium conditions, the right diet and you choose molly fish with good genetics.

12. They come in many different colors

In terms of colors, mollies come in green, orange, black, chocolate, white with black spots, gold dust, etc.

Popular molly fish breeds include the sailfin molly (long-finned variety), balloon and dalmation.

13. They’re algae eaters

Mollies enjoy picking at algae growing on the side of the tank and although they aren’t as prolific algae eaters as other freshwater fish, they certainly do help in keeping algae growth under check.

Of all the molly breeds, the black molly is probably the best at eating algae.

14. They like a planted aquarium

Not only that molly fish love to graze on algae, they also enjoy nibbling on live plants in the tank.

Adding hardy plants like hornwort to your molly fish tank can go a long way in making their environment more hospitable.

15. They don’t like small aquariums

Molly fish reach sizes of around 4 inches and they’re very active fish that enjoy swimming around in the aquarium.

Even though they aren’t big fish, they do require a large aquarium.

Most experts recommend at least 20 gallons tanks for these fish or even bigger for better results.


The funs facts about molly fish I presented in this article are generally applicable for the species.

However, differences can exist from molly breed to breed, so I advise you to research the type of molly fish you are considering keeping.

In particular, take care to match their water parameter preferences, temperature requirements, and other tank environment aspects.

Choose compatible tank mates, so that fights, injuries, and stressful conditions are avoided.

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