Skip to Content

What Is The Molly Fry Survival Rate?

Disclosure: When you purchase something through my affiliate links, I earn a small commission. As an Amazon Associate, I earn from qualifying purchases.

It can be pretty exciting to see a pregnant molly releasing her fry. But when I first saw it, I couldn’t help but wonder how many of these delicate creatures are expected to survive. Fortunately, over the years, I gained experience in this field.

On average, fifty percent of the molly fry should survive and reach adulthood. However, it is possible to improve their survival rate by taking the proper steps, including adjusting the water parameters and the feeding routine.

As we move forward, I will elaborate on the average molly fry survival rate and provide a few tips to increase this number. Surprisingly, some fish owners are able to keep all their molly fry alive.

A recently born molly fish fry that still hasn’t developed colors yet.

Still curious? Feel free to check my complete guide on molly fry. There, I discussed how to care for molly fry, what they eat, how often to feed them, their growth stages, and much more.

What Is The Molly Fry Survival Rate?

It depends on the conditions in the tank. Molly fry are minuscule, and most of the common freshwater species can swallow them whole.

Therefore, if you don’t protect the creatures, you could lose them all in a week. This is not a problem if you want the babies to die.

After all, a female molly can produce up to a hundred fry, and some aquarists don’t have the space to house them all.

Therefore, they will leave the creatures at the mercy of their parents and the other adult fish in the tank. The objective is to lose as many of them as possible.

In fact, it isn’t unheard of for aquarists to breed mollies with the intention of feeding the offspring to the inhabitants of the tank. Mollies are omnivores. They consume animal and plant matter.

However, it can take the creatures six months to mature, and they need as much protein as you can give them during the earliest stages of life. While they can survive on flakes and pellets, live foods are the best option.

If you want the babies to survive, you can expect roughly half of them to reach adulthood. This is not true in every case, as some people save all their mollies.

Although, that is rare because many fry are deformed at birth. This isn’t always obvious. It can take a few weeks for the deformities to become apparent. Once that happens, you are better off euthanizing the babies.

Some people have theorized that livebearers produce numerous offspring because many of them are lost at birth. Therefore, they need to maximize the number that survives.

You cannot accurately calculate the mortality rate of molly fish fry because various factors influence the final figure. Ultimately, your only option is to hope for the best, but only after taking every precaution at your disposal.

A couple of days old molly fry, searching for leftovers on driftwood.

How Do You Help Molly Fry Survive?

At the end of the day, the mortality rate of your mollies will depend mainly on the steps you take to protect them, of which there are quite a few, including:

1. Separate The Mother In Time

Move the mother to a safe place, preferably a separate tank. Breeder boxes are appealing, but they can induce severe stress, compelling the mother to abort her babies. A separate tank is the safer option. 

Look for signs of pregnancy in the female molly, such as the distended belly and darkening gravid spot. The females will become sluggish over time.[1]

You will observe obvious signs of nesting. Use that opportunity to send the mother to a place where she can give birth in peace. 

Female mollies can give birth in community tanks, but the other fish will eat the baby mollies. They can rarely survive in the main tank.

This pregnant molly has already developed a dark gravid spot.

2. Feed Your Molly Fry Properly

Food will have a drastic impact on the survival rate of Molly fish fry. The International Journal of Pure and Applied Zoology published a study designed to explore the effects of different protein-based formulated diets on the development of black mollies.[2]

All the animal protein-based formulated diets included in the experiment produced average growth. This shows that the expensive fish diets some aquarists prioritize are not necessary to increase the survival rates of baby mollies.

Like their adult counterparts, molly fry require nutritious meals delivered at consistent intervals. That includes flakes, pellets, baby brine shrimp, worms, and more.

Grind the food into a fine texture and feed the babies several times a day.[3] You have to restrict an adult molly to 2 or 3 meals daily. But the babies have voracious appetites. 

They can eat five or more meals each day. Overfeeding is not dangerous during the first few weeks of a molly fry’s life. 

A paper in the International Journal of Fisheries and Aquatic Studies observed that mixed live feed increases the survival rate of black mollies.[4] Therefore, you should endeavor to add variety to the meals your baby mollies eat.

  • For your convenience, here is a detailed Youtube video that shows how to make molly fish fry food at home:

3. Perform Routine Water Changes

Overfeeding is not a problem in the conventional sense because baby mollies have enormous appetites. They need to eat multiple times a day. 

However, overfeeding is a threat to the chemical balance of the water. Even with their insatiable appetites, baby mollies cannot eat all the food you’ve added. 

Some leftovers will sink to the bottom, where they will rot if you ignore them. Rotting leftovers are nothing to scoff at, as they will increase the ammonia concentration in the tank. 

Adult mollies can survive ammonia poisoning, but the same cannot be said for their offspring. Water Changes won’t remove the leftovers. 

However, you can trust them to keep the ammonia concentration under control. You should change 20 percent of the water twice a week.

You would expect aquarists to change more significant portions of the water to make ammonia less of a threat. However, the stress a significant water change induces may kill the baby mollies.

Aim for these water parameters for molly fish fry:[5]

  • Temperature: 75°-80°F (24°-26.7°C)
  • pH: 7.5-8.5
  • GH: 12-25 dGH (200-416 ppm) 
  • KH: 10-25 dKH (178-450 ppm)
  • Ammonia/Nitrite: 0 ppm
  • Nitrate: <30 ppm

To measure the ammonia, pH, nitrate, and nitrite, I personally use the API Water Test Kit (link to Amazon). This one is exceptionally reliable and lasts for hundreds of measures.

As for the water hardness, you can simply go with the API GH & KH TEST KIT (link to Amazon). This one is pretty affordable and easy to use.

If you see that the ammonia keeps spiking, the first step you should take is vacuuming the substrate. Also, when cleaning the aquarium, skip on the filter media.

This part usually contains essential bacteria that turn ammonia into nitrite. You can wash the debris out of it, but make sure you use the aquarium water, not tap water.

A pregnant molly fish that is about to give birth.

4. Keep The Temperature Stable

You’re unlikely to keep the baby mollies alive without a heater. Even though the fry appreciate warm water (it enhances metabolism), you don’t want the temperature to exceed 80 degrees.

It is worth noting that fry will eat more food in warm water. On the one hand, they will grow at a faster rate. But on the other hand, they will produce more waste.

Another critical step is keeping the temperature stable. That is even more important than keeping the temperature within the desired range (75°-80°F).

Molly fry that are exposed to frequent fluctuations will get stressed and possibly die. With a good heater, you shouldn’t see the temperature change by more than 1 degree F.

5. Get The Right Filtration System

You need a proper filtration system to keep the water clean. Water changes are effective, but they can’t remove waste and leftovers from the aquarium, not without help.

Many aquarists are hesitant to install conventional filters because they are strong enough to suck the babies in. But you can buy attachments that make filters less dangerous to baby mollies.

Filters play the same role in a nursery tank as they do in a community tank. They house nitrifying bacteria that turn ammonia into harmless nitrates. 

Therefore, don’t be tempted to maintain a nursery tank without a filter. These devices are essential to the fry’s environment.

If you don’t have a filter yet, I personally recommend getting the Lefunpets Sponge Filter (link to Amazon). It worked perfectly in my molly and guppy fry tank.

6. Add A Few Plants

Add some live plants to the aquarium. Artificial plants will work, but live plants are better because they add oxygen to the water. 

They also provide hiding spots which are essential for baby mollies living in community tanks. From my experience, floating plants with brushy roots work best.

These are the plants I recommend for a molly fry tank:

  • Amazon Frogbit (Limnobium laevigatum) 
  • Red Root Floater (Phyllanthus fluitans) 
  • Water Lettuce (Pistia stratiotes)
A mystery snail and a molly fish fry, living peacefully with each other.

If you found this article helpful, these may also interest you:

Conclusions

It isn’t easy to keep all the molly fry alive, especially if the mother has given birth to a hundred of them. On average, half of the fry will die during the first couple weeks.

You can minimize the deaths by taking a few measures upfront. First, make sure you feed the fry various protein-riched foods. Grind the food properly so that it fits in their mouths.

Then, adjust the water parameters, especially the temperature. Swings are acceptable, but they shouldn’t exceed 1 degree F.

References

  1. https://www.cuteness.com/article/tell-fish-ready-give-birth
  2. https://www.alliedacademies.org/articles/growth-and-survival-of-fingerlings-of-black-molly-poecilia-sphenops-with-different-animal-protein-based-formulated-diets.pdf
  3. https://www.wikihow.com/Take-Care-of-Molly-Fry
  4. https://www.fisheriesjournal.com/archives/2014/vol1issue6/PartA/139.pdf
  5. https://modestfish.com/molly-fish-care/