How Do You Keep Molly Fry Alive? (7 Simple Steps)

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It is pretty exciting to have a batch of molly fry. However, because they live in an aquarium and not in nature, it is essential to take a few measures to keep them alive. Fortunately, over the years, I have gathered some excellent tips on that topic.

These steps will help you keep your molly fry alive:

  • Isolate the fry by using a breeder box or a breeding tank.
  • Pick a tank of about 20 gallons (preferably a tall one).
  • Prioritize foam filters so that the fry don’t get sucked into it.
  • Aim for a temperature of 75-80° F (24-27° C).
  • Place a few plants to provide shelter and oxygen.
  • Acclimate the fry when placed in a new tank.
  • Grind their food so that it fits in their mouths.

As we move forward, I will elaborate on the different steps that will help you keep your molly fry alive. Then, I’ll discuss what fish will probably eat them and whether you can use a bowl to grow these delicate creatures.

Also Read: Molly Fry 101

One week-old molly fry, swimming freely in its nursery.

How Do You Keep Molly Fry Alive?

Mollies give birth to live fry, which is technically good because the babies can swim to safety. However, don’t expect molly fish fry to survive alone. 

On average, fifty percent won’t survive even when taking the proper measures. So, you shouldn’t expect any of them to reach adulthood unless you take the following actions:

1. Isolate The Baby Mollies

You have to start protecting the fry before they emerge from the mother’s belly. A female molly can give birth in a community tank, especially if it has plants and decorations.

The females can use these objects to hide from predators. However, a female molly in a community tank is more likely to struggle with stress, particularly in settings with bullies.

That stress can cause the mother to lose some or all her babies. Therefore, where possible, place the mother in a separate tank. Allow her pregnancy to advance in a stress-free environment.

You can also install breeder boxes in the community tank. People love them because you don’t have to spend money on filters, heaters, air stones, or other accessories a conventional tank requires.

If you pay close attention to the mother’s gravid spot, you can use the changes in the mark to track the development of her pregnancy.[1]

If you can move her to the breeder box before she gives birth, the mother will drop the babies into a separate compartment below.[2]

Remove the female molly from the breeder box and then decide whether you will leave the fry in the breeder box or move them to a separate container.

The molly fish’s gravid spot (seen in the posterior part of the lower abdomen).

2. Pick A Relatively Large Tank

Even though molly fry are small, they still need a sizable tank. They won’t grow to fit the size of a small tank, which is what some aquarists assume. 

Instead, the crowded conditions will kill them, especially if you permit the ammonia levels to go unchecked. You need at least five gallons, although 20 gallons will provide the best results. 

If you want the nursery tank to hold the mother before she gives birth, make sure the nursery tank is large enough to house the mother.

You should also take the tank’s shape into account. Wide tanks can be problematic as the fry may not find the food or get too tired searching for it.

That is why I suggest getting a relatively tall tank, such as the Tetra ColorFusion Aquarium 20 Gallon Fish Tank Kit (link to Amazon). This one is 20.38 inches in height, which is pretty decent.

3. Get A Proper Filtration System

The filtration is tricky because you can’t just pair the nursery tank with a conventional filter, as the fry will get sucked into it. 

You can still use a traditional filter, but only if you buy an attachment that makes the device less dangerous. If you don’t have the money, you can also use pantyhose. Otherwise, prioritize foam filters.

Also Read: What Do Molly Fry Need?

4. Adjust The Water Parameters

Molly fry are smaller and, therefore, more sensitive to the wrong parameters than their adult counterparts. The nursery tank requires a temperature of 75 – 80 degrees F.

You can’t maintain this temperature without a heater. Warm water will enhance the growth of the babies by boosting their metabolism. Keep a thermostat on hand and test the water routinely.

Aim for a pH between 7.5 and 8.5.[3] Besides being in that range; it is also essential that the pH remains stable. You can achieve that by performing routine water changes.

The ammonia and nitrite should be at 0 ppm, while nitrates are below 20 ppm. You can measure these with a test kit. I personally use the API Water Test Kit (link to Amazon).

5. Scatter Plants With Brushy Roots

People associate plants with community tanks because they provide hiding places for molly fish fry during the most fragile stages of their lives.[4] But plants are just as important to babies in nursery tanks.

First, they generate oxygen while simultaneously absorbing carbon dioxide, reducing the chances of an oxygen deficiency taking root. Secondly, hiding spots put the fry at ease, repelling stress in the process.

These plants will work best in a molly fry nursery:

  • Amazon Frogbit (Limnobium laevigatum) 
  • Red Root Floater (Phyllanthus fluitans) 
  • Water Lettuce (Pistia stratiotes)

These ones have brushy roots that provide excellent coverage for the molly fry. In some cases, the babies will choose to hide under a floating plant. That is perfectly fine.

Amazon frogbit (Limnobium laevigatum) in a backyard pond.

6. Ensure The Fry Acclimatize Properly

If you bought the molly fry from a store, take a moment to acclimate the creatures to the conditions in the nursery. This process sounds inconvenient, but it can take 15 minutes or less.

Take the bag with the fry and allow it to float on the surface of the nursery. The temperature in the bag will change to match the temperature in the aquarium.

Without proper acclimation, the shock of the transition will kill the babies. Even after acclimating the babies, take a moment to watch them once they enter the new tank. 

Take them out if they display signs of stress, such as erratic swimming and lethargy. Some fry will die during the journey from the fish store. You won’t identify them until you pour the babies into the nursery.

Once you locate the dead babies, remove them. Otherwise, they will kill the other fry by decomposing and producing ammonia, which is toxic.

7. Feed The Fry Adequately

A study from 2012 (University of Maryland Center For Environmental Science) found that probiotics could accelerate development in baby fish.[5]

But you don’t have to invest in crates of yogurt to keep molly fish fry alive. They will eat the same foods that adult fish enjoy.

But you have to grind them into smaller pieces to accommodate the small mouth of a baby molly.

They will eat baby brine shrimp, Hikari, daphnia, micro worms, and more.

If all that sounds intimidating, below is an excellent Youtube video that will show you how to make molly fry food at home.

Also Read: Molly Fry Food

What Fish Will Eat Molly Fry?

Baby mollies eat microscopic foods at birth because the creatures are tiny. This is problematic because adult fish will eat anything that fits in their mouths. It isn’t a question of temperament.

Adult mollies are peaceful, and yet, that won’t stop them from eating baby mollies. That is why I typically suggest removing the mother as soon as she’s done giving birth. 

The same is true for swordtails, platies, angelfish, and every other species whose size exceeds that of a baby molly.

If you insist on growing other fish with your molly fry, I would personally go with bottom dwellers. That includes Bristlenose Plecos, Cory Catfish, Kuhli Loaches, etc. They will rarely eat any fry.

Can I Keep Molly Fry In A Bowl?

No. A bowl is a poor substitute for a proper nursery tank. Female mollies can produce as many as a hundred babies. A bowl cannot accommodate them all, not comfortably.

A bowl is a short-term solution capable of housing baby or even adult fish in an emergency. But you cannot expect baby mollies to survive in a bowl in the long term.

First of all, bowls create crowded conditions. You can’t even afford to add plants and decorations because they will only make the crowding worse.

Secondly, you cannot attach heaters to bowls. This doesn’t matter if you typically rely on the ambient temperature to keep the fish happy. 

But because bowls are so small, the water temperature is more likely to fluctuate. Baby mollies are too fragile during those first few days. They cannot survive drastic shifts in temperature. 

Unfortunately, the temperature is the least of your worries. Because of insufficient filtration, ammonia will spike frequently and dramatically, killing the babies.

Bowls are not worth the hassle, as you will lose a significant portion of your molly fry population. Avoid them by all means.

A five-day-old molly fish fry that hasn’t developed colors yet.


Molly fry are considered hardy. However, that doesn’t mean you should let nature take its course. If you don’t take the necessary measures, your fry aren’t likely to survive.

Start by keeping the mother stress-free before and during birth. Do that by removing aggressive tankmates, including the father itself.

Then, focus on the environment and make sure it is fit for molly fry. That includes adjusting the water parameters, introducing plants with brushy roots, and feeding the fry properly with various foods.