Are Mollies Hardy Fish? {Bullies or Bullied?}

Do you wonder if molly fish are resilient and tough in the tank? Are mollies hardy fish?

Are you concerned that they won’t be able to thrive in your fish tank? Do they get bullied or are they the bullies themselves?

Let’s take a closer look in this article I wrote so we can get to the heart of this hardy topic.

Are Mollies Hardy Fish?

Yes, Mollies are hardy fish and easy to care for and should live 3-5 years if they are kept in ideal water conditions.

Molly fish can live peacefully in a tank with various species of fish. They are freshwater fish and very popular for good reasons.

The best news is that most species of mollies are hardy, but there are some important details to dive into.

Are Mollies Hardy

Are Mollies Sensitive Fish?

Yes. Even if we label animals or humans as being hardy or tough, it doesn’t mean that they can’t also be sensitive. The same is true for molly fish. They are indeed sensitive to other aggressive or animated fish swimming around them.

Cichlids for example, are considered more aggressive than mollies. They can disturb or cause stress to molly fish. Larger aquariums or fish tanks can help to allow them more space to avoid these stressful encounters.

Male molly fish pursue the females in their attempts to mate with them. An environment with more vegetation gives the females more opportunities to hide from these males.

Open areas with lots of swimming space also helps to reduce the sensitivity to other fish they cohabitate with.

Are Balloon Mollies Hardy?

No. Balloon mollies or pot belly mollies are considered hardy compared to many other fish. This type of molly fish has inherited a defect where its spine has extended in an abnormal way.

If we compare most mollies with balloon mollies, we’ll find that the latter is less hardy.

Balloon mollies are known to have:

  • more health problems
  • shorter lives
  • intestinal issues
  • constipation 
  • a genetic defect they pass on to their offspring.

If they mate with other molly fish, the sensitivity levels in the fry may increase. If you want your molly fish to survive for a long time, it’s best to avoid balloon mollies.

Are Balloon Mollies Hardy

Can Mollies Be Kept Outside?

Outdoor temperatures are very important to consider when answering this question. Did you know that mollies are tropical fish? They enjoy warmer temperatures, but once again, they are hardy!

There are some individuals who say that they’ve kept mollies in cooler outdoor temperatures. Here are some risks to consider in cooler climates:

  • Vulnerable to more diseases
  • Stunted growth
  • Difficulty mating
  • Inability for pregnant females to give birth

Ideal Molly Fish Temperature

Temperatures of 16°-20°C or 60°-68°F are not ideal for these hardy fish, but they can survive. Pushing the limits may cause them to act lethargic and decrease their lifespans.

  • Molly fish enjoy climates at 24°-26.7°C or 75°-80°F.

Molly fish are resilient and able to live in lower temperatures between these listed ranges. A heater is still recommended in colder climates or to maintain a constant temperature.

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How Long Can a Mollie Not Eat For?

Molly fish are a great choice for those of us who are forgetful or just too busy. Adult mollies can survive without eating for as long as two weeks. Younger mollies who are recently born in a fry need food within three days.

When comparing mollies to other popular types of pet fish, they are better able to withstand hunger and starvation. Two weeks is on the upper end of the scale. Move aside goldfish and guppies! Mollies are here to stay!

What Water Conditions Can a Mollie Survive in?

Mollies enjoy freshwater, but slightly brackish waters are also fine. They are robust and strong enough to not be so picky, so try not to worry too much.

They can adapt to slightly brackish waters that are a little salr 90 liters would be preferred for 4-8 mollies.

Decorating the tank with hiding spaces mixed with ample open areas gives mollies favorable water conditions to enjoy their lives. They can steer clear of other aggressive males and live peacefully.

Do Mollies Need a Heater?

Molly fish are hardy and able to survive without heaters in some cases. They don’t like drastic shifts in climate. A heater helps to maintain a constant temperature. Mollies routinely fall into most top ten lists for the best freshwater fish to keep in an aquarium. 20 gallons of water o

A fry of mollies would definitely benefit the most from a heater. This would allow them to grow and thrive under ideal conditions.

An adult molly fish would also enjoy a longer life of about 3-5 years if their water is cleaned regularly and kept warm with a heater.

Are Molly Fish Aggressive?

Yes and no. Typically, mollies don’t have a bad reputation for attacking other species. If they feel threatened or are trying to create a pecking order among themselves, especially if new fish have just been put to the tank, they are capable of being mildly aggressive against other mollies

Others in their aquarium have been known to have their fins nipped by them. While eating, mollies will occasionally chase and attack other mollies, although they won’t do much damage

If your tank is too tiny, the bullied fish won’t receive any food at all. It might pass away from illness and stress.


If you decide that you want a hardy fish that survives and thrives in your aquarium, the molly fish is a great choice. If you care for them better, they will survive even longer.

Try not to beat yourself up if you miss a feeding or forget to clean the tank. These fish are robust and healthy enough to withstand our blunders and forgetfulness.

Maintaining ideal temperatures are important for so many creatures, but some are more resilient. Your molly fish would like to be warm, but they’ll forgive you sometimes because they are indeed hardy.


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Hello, I'm Jason. I'm the guy behind I volunteer at my local fish shop and I created this site to offer tips and advice on the fish I care for.