Can Molly Fish Live Without Oxygen?

I often get asked this question by people that are just starting out with in the hobby. It may seem like an absurd question at first, until you realize it actually enquires about the need for the water bubbles produced by an aquarium air stone.

So, can mollies live without oxygen? Of course not.


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But do they need an air stone or water pump in the aquarium? Yes, I would say they do.

A water pump, air stone or anything else that drives oxygen into the water is certainly desirable for your molly fish.

Let’s see what these devices do, how do molly fish breathe, and how does oxygen exchange work in water.

How Oxygen Exchange Works

Molly fish breathe dissolved oxygen in their water, and they do so through their gills. Some fish require oxygen-rich water and when oxygen levels drop in the aquarium, you’ll often see these fish swimming close at the surface of the water.

Despite water (H2O) containing oxygen, fish require oxygen molecules (O2) to survive. You can introduce oxygen to an aquarium, by agitating the water, so that oxygen from the atmosphere gets into the water.

The higher the surface agitation, the more oxygen gets into the water. You can also add fresh water to the aquarium, which contains dissolved oxygen molecules.

Do Mollies Need an Air Stone or Water Pump?

Since oxygen is indispensable for molly fish, you’ll need to promote oxygen exchange, so that enough oxygen gets into the aquarium and meets the oxygen needs of your molly fish.

Installing a water pump or placing an air stone into the aquarium will facilitate oxygen exchange by agitating the surface of the water.

An air stone may be a better choice for a smaller aquarium, while a larger aquarium would benefit better from a water pump that will agitate the water much better.

For good oxygen exchange and to provide your molly fish enough oxygen, make sure you invest in a quality water pump. Pick one that is less noisy, so you don’t stress your fish out.

Oxygen rich water is essential for some fish and the easiest way to offer them that is to have a water pump in your aquarium.

Live Aquatic Plants – Another Way to Promote Oxygen Production in Your Aquarium

Another way to promote oxygen exchange is to add live plants to the aquarium. Water pumps and air stones can be noisy, and you may want an alternative to them.

And what better alternative than what Mother Nature herself provides for the purpose of driving more oxygen into the water?

Live plants help create an all-natural and self-sustaining ecosystem that can be perfect for your molly fish.

Live plants will feed on the CO2 released by your fish along with nitrates, while molly fish will consume the oxygen released by the live plants in your aquarium.

Therefore, you can create a mutually beneficial and self-sustaining environment. Plus, if the proportion between live plants and molly fish is adequate, you can get away with having live plants in your aquarium instead of a water pump.

The problem with live plants, however, is that they require maintenance, some require dosing with fertilizers, others require a lighting system.

If you’re still a beginner, you may not want to invest in all these, therefore, I recommend that you opt for low light and hardy plants like the ones listed below:

  • Crypt Wendtii;
  • Hornwort;
  • Waterweed;
  • Amazon Sword;
  • Java Moss;
  • Micro Crypt;
  • Anubias Nana.

With a planted tank, I recommend choosing an all-in-one aquarium substrate like ADA Aqua Soil, which comes pre-packed with all the nutrients required for healthy plant growth and development.

Do Molly Fish Need a Water Filter?

Apart from a water pump or air stone to keep the aquarium water well oxygenated, another indispensable equipment for your mollies is a water filter.

A water filter will remove toxins and waste products from your aquarium, keeping the water clean and clear.

There are many things in the aquarium that can release toxins and wreak havoc when it comes to the chemical balance established as a result of the nitrogen cycle.

One such thing is the waste produced by your mollies. Mollies have an almost insatiable appetite and can eat quite a lot. This results in a higher waste production that can disrupt the water chemistry.

Besides the waste produced by your fish, uneaten food that’s left to decompose in the tank also causes ammonia levels to spike in the tank.

This is where an internal water filter comes in. It helps reduce waste products and can help agitate the water, so that more oxygen can get into it.

Beyond its water clarifying benefits, a water filter has a filter media that provides quite a lot of surface area for beneficial bacteria to develop.

The bacteria that colonize the filter media help in transforming ammonia into nitrites, and nitrites into nitrates during the nitrogen cycle, and they continue helping to maintain a healthy water chemistry later on.

If you have fry in your tank or planning on breeding your fish, you can get a sponge filter or transform your internal filter so that it’s fry-safe.

Since baby fish are so small, they can easily get sucked into the filter system.


Molly fish can’t survive without oxygen and anytime the oxygen levels in the tank drop, your fish are exposed to illnesses and diseases.

Therefore, beyond stimulating oxygen exchange with an air stone, water pump or by planting live plants in your molly fish tank, make sure to also:

  • Regularly perform water changes;
  • Vacuum the substrate and clean tank surfaces;
  • Rinse filters;
  • Don’t overfeed your fish;
  • Remove any uneaten foods.

If you abide by these tips and recommendations, you’ll be able to offer your molly fish a healthy environment.

Because aquariums are a closed ecosystem, maintenance tasks should be performed regularly to maintain the water chemistry and balance that was created during the nitrogen cycle.

I hope my article has answered your questions about the oxygen requirements of molly fish and the systems that should be deployed to ensure proper oxygen exchange in the aquarium water.

Questions and Answers

I have 6 mollies, 3 males and 3 females. I just put them in a round transparent ice cream container. I have them since February so its been more than 5 months now. I feed them with flakes or floaters. They dont have oxygen or air pump but they still manage to survive by changing the water every other day. The only thing I am sorry for is that Females got pregnant and Im not aware of it so the new borns did’nt survive. The water gets cloudy and I have noticed tiny frys about 15 lying lifeless at the bottom. Maybe because of the water condition. To tell you honestly I became too busy that week that I have set aside to change the water. Almost forgot it unti I noticed that it became cloudy and dirty. I learned a lesson from there. Now my female mollies were about to give birth again, I have separated them to another container to be sure. But this time I put bubble stone for the oxygen of the tiny frys. By the way, 2 frys were born this morming and hoping for more this week.

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