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Molly Fry 101: Care, Food, Growth, Survival Rate & More

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Even after years of experience, I acknowledge that raising molly fry can be difficult. That is especially true for those who are new to fishkeeping, as molly fry come with many questions.

So, after quite some time, I decided to gather some of the most common questions into one thorough article. In many cases, I will link to another article I wrote so that you get the picture in detail.

Ultimately, in the second part of this article, I will list some essential tips that will help you care for your molly fry and keep a large portion of them alive.

For those of you who are in a rush, here is a table that gathers some of the most crucial information on molly fry:

Feeding frequencyFive times a day
Separation durationTwo months
Survival rate~50%
Tank size10-20 gallons
pH7.5-8.5
Temperature75°-80°F (24°-26.7°C)
General hardness12-25 dGH (200-416 ppm)
Carbonate hardness10-25 dKH (178-450 ppm)
Ammonia0 ppm
Nitrite0 ppm
Nitrate<20 ppm
A transparent molly fry, digesting its meal.

What Do You Do With Molly Fry?

These are the courses you can take with molly fish fry:

  • Raise the babies in their own nursery. 
  • Leave them in the community tank.
  • Sell the fry to a fish store. 
  • Give the babies away to other aquarists. 
  • Trade the molly fry for other fish. 

Dealing with molly fry for the first time can be overwhelming, especially if they catch you by surprise. In the second part of this article, I will show you how to raise them properly (assuming you go with the first option).

But you don’t have to keep the fry if you don’t want to. Leaving them in the main tank can be pretty nutritious to the rest of the fish you own. Many fish owners go with that route.

You can also get rid of them by trading or selling them. You may be surprised to find out how many fish stores show great interest in those little creatures.

This molly fry found shelter behind driftwood.

Sounds interesting? Check out this article where I discussed what to do with molly fry. I distinguished the steps you can take with wanted fry from those of unwanted fry and elaborated on each.

How Many Fry Can A Molly Fish Have?

Molly fish typically deliver between 40 and 100 live fry in a single session, but that isn’t always the case. Some mollies will produce less fry because they haven’t fully matured yet or are highly stressed.

If you suspect that your molly fish is pregnant, there is a high chance she will deliver a lot of fry in a single batch. However, many factors can prevent this from happening.

For example, if the temperature consistently fluctuates, the female will be stressed and possibly absorb some of the fry. Also, some mollies are just too old or young to deliver so many fry.

Still curious? Click here for more information on how many fry can a molly fish have. I also discussed how often molly fish deliver and how you can ensure that the fish gives birth without complications.

What Is The Molly Fry Survival Rate?

About fifty percent of the molly fry eventually survive and reach adulthood, but you can improve the survival rate by taking a few steps. That includes adjusting the water parameters and the feeding routine.

As previously discussed, mollies can deliver up to 100 fry in a single batch. But that doesn’t mean all of them will survive. In a typical tank, about half of the fry will die. 

You can improve this number by raising the fry in a dedicated nursery. If you can’t do that, ensure there are plenty of hiding places in the community tank.

You should also feed the fry properly. Just remember that their feeding schedules and food types are slightly different from adults.

As I’ll explain later, molly fry can eat whatever adult mollies eat, but you have to grind the food into tiny pieces. They also eat more frequently than adults (up to five times a day).

Caught your attention? Here you can find more information on the molly fry survival rate. You will find a step-by-step guide to improve this number and bring it to the maximum.

What Do Molly Fry Eat & How Often?

This table summarizes what molly fish fry eat, depending on their age:

The Food TypeAt What Age
InfusoriaUntil day 7
Baby brine shrimpBetween days 7 and 21
Freeze-dried/frozen foodsDay 21 and beyond
WormsFrom week 5 and beyond
Flakes/pelletsFrom week 8 and beyond

As you can see, molly fry eat different kinds of food, depending on their growth stage. Start with infusoria up to week one. This is highly nutritious, microscopic food that fish fry love.

Then, you can move on to larger types of food, such as baby brine shrimp, freeze-dried food, worms, pellets, flakes, etc.

While it is highly recommended, you don’t have to change the fry’s diet at different stages. You can stick with one type of food, although I suggest mixing at least two. Just make sure it is small enough to fit in their mouths.

Until one month, you should feed the fry about five times daily. Give them the amount they can finish within two to three minutes.

During their juvenile stage (days 30-60), you can cut the meals to 3-4 times daily. After two months, the fish reach their fingerling stage and can be fed twice daily.

A few days old molly fish fry, eating algae grew on a plant.

Wish to learn more? Check out my complete molly fry feeding guide. In there, I take you step-by-step through the process of feeding these delicate creatures. I also included some excellent videos for a better visual understanding.

What Are The Molly Fry Growth Stages?

These are the general molly fry growth stages:

  • Stage 1 (days 1-30) – The fry are transparent and vulnerable. 
  • Stage 2 (days 30-60) – The reproductive organs are revealed for the first time.
  • Stage 3 (months 2-4) – The mollies reach sexual maturity. 
  • Stage 4 (months 4-6) – The mollies are considered adults and no longer grow.

Up until day 30, the baby mollies are considered fry. You won’t be able to spot any colors or tell if a fish is a male or a female.

During that stage, they are incredibly vulnerable. Most of those who won’t reach adulthood will die during the fry stage (about fifty percent).

After thirty days, you should recognize the breeding organs. You may see the males’ gonopodium and the females’ gravid spot (representing the womb).

After two months, during the fingerling stage, the mollies are about 4 to 6 inches long and ready to reproduce. If you wish to avoid that, you should separate the males from the females at this point.

Sounds interesting? Feel free to visit the article where I discussed the molly fry growth stages. Besides detailed pictures, I included a fascinating video that follows the fry’s growth until day 32.

When Do Molly Fry Get Their Color?

Molly fry start developing colors during their first month. However, these will probably change and become more intense as the fish grow. At four months of age, the young molly will achieve its final appearance.

While it can take a few months for the fry to develop colors, you can take a few steps to accelerate this process. The key is to keep the fry healthy.

You can do that by maintaining a relatively warm environment (about 80 degrees F) and feeding the fry adequately.

Still curious? Check out this article where I discussed when molly fry get their colors. I made sure to list all the steps you should take to achieve the most beautiful and colorful molly fish.

What Equipment Do Molly Fry Need?

Here is a table that shows what equipment molly fry typically require:

EquipmentHow Necessary?
FilterVery
HeaterVery
Air stoneSomewhat
LightsSomewhat
Air pumpNot necessary

If you grow your molly fry in a nursery, you must equip it with the same devices you would offer adult fish. That includes a functioning filter and heater. These two are the most crucial.

Then, you can add an airstone and lights. The airstone isn’t mandatory, although it becomes useful if the tank holds a few dozens of fry.

A lightning system is also beneficial because it helps you create a day/night cycle. Aim for 10 to 12 hours of lights, and don’t forget to turn them off during the night.

Caught your attention? Click here for more information on what equipment molly fry need. I made sure to include the particular gear I use when growing a new batch of fish fry.

Will Molly Fry Survive In The Main Tank?

Molly fry rarely survive in community tanks. Ideally, they should be raised in a nursery for about two months. Afterward, they will enter their fingerling stage and be too large to fit in adult fish’s mouths.

Keeping the molly fry in your main tank isn’t ideal. They will be chased down and eaten by adult fish. If you must do that, ensure you place a sufficient number of hiding places.

You can use decorations, plants, etc. If you have the time, investing in floating plants with brushy roots is excellent. Fry love getting behind those. These are the ones I recommend:

  • Amazon Frogbit (Limnobium laevigatum) 
  • Red Root Floater (Phyllanthus fluitans) 
  • Water Lettuce (Pistia stratiotes)
Three days old molly fry, swimming at the top of the tank.

Wish to learn more? Click here for more information on whether molly fry can survive in the main tank. If you can’t start a nursery, you will find everything you need to raise them in your community tank.

What Fish Will Eat Molly Fry?

Here is a table of a few common freshwater fish and their relationship with molly fry:

Fish TypeWill They Eat Molly Fry?
MolliesYes
AngelfishYes
BettasYes
GuppiesYes
Neon TetrasProbably
Dwarf GouramisProbably
RainbowfishProbably
Bottom DwellersNo

If you raise your molly fry in the main tank, remember that some fish are more aggressive than others and may chase them down.

Adult mollies, angelfish, bettas, and guppies won’t hesitate to ear the fry. If you own those, don’t introduce the fry until two months of age.

Neon tetras, dwarf gouramis, and rainbowfish are less dangerous but should also be avoided if possible. 

Bottom dwellers like cory catfish aren’t a danger to molly fry at all, and they can happily share the same tank. If some of the fry go missing, they probably died for other reasons. 

As a rule of thumb, any mid and top dwellers that can fit the fry in their mouths are a danger to molly fry. Introducing dense foliage with those types of fish is crucial.

Sounds interesting? Check out this article where I explained what fish would eat molly fry. I also listed a few tips that may help you raise the fry with adult fish.

How Do You Keep Molly Fry Alive?

These are the general steps you should take to keep molly fry alive:

  • Isolate the fry with a breeder box or a breeding tank. 
  • Choose a tank of about 20 gallons (avoid larger ones). 
  • Pick a foam filter to prevent the fry from being sucked. 
  • Keep the temperature between 75 and 80° F (24-27° C). 
  • Scatter live plants for shelter and oxygen. 
  • Acclimate the fry if placed in a new tank. 
  • Grind the food into tiny pieces before feeding them.

Following those steps will increase the survival rate of your molly fry drastically. They are great if you are in a hurry and wish to keep the fry alive. However, in the second part of this article, I will show you how to care for the fry more thoroughly.

This two-week-old molly fry started to develop some colors.

Still curious? Check out this article where I explained how to keep molly fry alive. In there, I elaborate on each step that I mentioned earlier.

How Do You Care For Molly Fry?

Adult mollies produce live babies. When the fry arrive, you can either raise them or donate the creatures. If you’re hellbent on raising the baby mollies, you will most likely follow these steps:

1. Choosing The Right Tank (10-20 Gallons)

Even though molly fry are small, you cannot keep them in a bowl. They need more space. Otherwise, the stress will kill them. But what is the appropriate size of a nursery tank?

Many newcomers are convinced that the biggest tanks are the best. That idea has been propagated by some professional aquarists who keep encouraging beginners to buy the biggest tanks they can find.

In a way, this advice is not wrong. There’s no such thing as a tank that is too large for adult mollies. But baby fish are different. They don’t have the same strength as their adult counterparts. 

As such, you cannot expect them to cross large distances to find food. The exhaustion will probably kill them. Some babies will starve because they cannot find the food you added. 

However, you can’t make the aquarium too small either. What do you think happens to the waste in a small aquatic space? When the waste rots, ammonia will rise at a much faster rate. 

Larger aquariums can dilute these toxins, protecting the babies from ammonia poisoning. The key is to find a balance. Aim for 10 to 20 gallons for the nursery tank.

20-gallon tanks, excellent for 50 molly fry or more.

Don’t be afraid to increase the tank size to match the number of molly fry. But again, don’t go overboard. 

You can keep molly fry in bowls during emergencies. The babies won’t die, not immediately. But you shouldn’t force them to linger in crowded conditions. Move them to a larger tank as soon as possible.

Money also matters. In an ideal situation, you should get the biggest tank the market has to offer (without going overboard). But larger tanks are more expensive.

Remember that the filter’s strength has to match the tank size. In other words, it isn’t enough to buy a large aquarium. Do you have the money to populate a sizable aquatic space with the relevant accessories?

If you have financial restrictions you cannot overcome, limit the number of molly fry. Stick with a population that can fit in the tank you can afford and give the other babies away.

Regarding the material, glass is the best option because acrylic scratches a little too easily. On the other hand, acrylic is also easy to repair. But if you have financial constraints, glass is the cheapest option.

2. Positioning The Tank Properly

You have to select the location carefully. Don’t forget: tanks are heavy. Once you install one, you can’t just move it at a moment’s notice. 

First of all, it has water. Secondly, you must remove all the hardware, including filters and heaters. The process is a hassle. 

Therefore, you should proceed cautiously. Consider the following:

  • Direct sunlight is a bad idea, as the algae will run amok. 

You cannot place the nursery tank next to a window unless you have an obstacle outside that can block the sun. Additionally, direct sunlight will raise the temperature.[1]

  • Keep the fry away from locations with heavy human traffic. 

The human activity outside can become a source of stress, especially if your home has people that keep tapping on the glass.

  • Even though you have to avoid human traffic, the aquarium should be easy to access. 

Fish don’t serve any purpose unless you can observe them. More importantly, you have to change the water every week. If you install the aquarium in a location with poor accessibility, you may neglect your maintenance duties. 

  • Avoid excessive noise. Don’t position the aquarium next to entertainment systems or loud appliances.[2]
Positioning the nursery next to a window isn’t recommended.

3. Picking The Right Filtration System

The filtration system is probably the most important accessory in the aquarium. Filters achieve two objectives, namely:

  • Filters remove pollutants from the water, preventing them from poisoning the fish.

Fish generate a lot of waste. That doesn’t even account for the leftovers that tend to accumulate in a nursery tank. You need a filter to keep the water clean.

  • Filtration creates agitation, which, in turn, prevents stagnation while also increasing the gaseous exchange at the surface. A strong filter can prevent oxygen deficiencies from forming if you don’t have air stones. 

To keep the tank clean, you have to account for all three components of a filtration system:

  • Mechanical filtration handles physical waste. It removes the fish poop, leftovers, and decaying organisms.
  • Biological filtration uses nitrifying bacteria to process ammonia, turning the toxin into nitrite. 
  • Chemical filtration isn’t always necessary. It removes dissolved waste. If your water is discolored, chemical filtration will clear it.

You must secure a filter that cleans the water without harming the baby mollies. Your options include:[3]

  • Canister – These are powerful enough to accommodate large aquariums. However, they are also the most expensive. You can change the filtration material with relative ease. 
  • Submersible – You attach these models to the glass using suction cups. The power head aerates the water. 
  • Hang On – This type mimics a waterfall. Hang-On filters use replaceable cartridges. 

Sponge filters are your best bet if you need a tried and tested option. They are the simplest and least attractive of the bunch.[4] However, they are also the least dangerous for baby mollies.

Conventional filters are problematic because they will suck the molly fry in. This is why the flow rate is so important. A strong flow rate will exhaust the molly fry. It can also kill them.

Bear in mind that with a new filter, you must cycle the tank for six weeks, possibly even more, to create the nitrifying bacteria that convert ammonia into harmless components.

For the best results, I would pick the Pawfly Aquarium Nano Bio Sponge Filter (link to Amazon). These are gentle and great for tanks up to 20 gallons.

And if you don’t have the time to cycle the nursery, you can simply get the API Quick Start Nitrifying Bacteria (link to Amazon). Here is a Youtube video that will show you how to use it:

4. Adding A Few Plants (Live/Artificial)

You don’t have to overthink a nursery tank’s plants. They exist to provide hiding places. You can also trust them to increase the tank’s oxygen content.

But that second function doesn’t matter quite as much because you can trust water pumps and air stones to perform that task. In the absence of plants, you should add driftwood, vases, caves, and other decorations.

People think plants only matter in main tanks where molly fry are trying to hide from adult fish. But hiding places are just as crucial in nursery tanks. They alleviate stress. 

5. Maintaining The Right Water Parameters

You cannot keep these creatures alive without maintaining a temperature of 75°-80°F (24°-26.7°C). Install a heater and keep a thermostat on hand.

Test the water whenever you perform a water change. A significant water change can easily alter the temperature, especially if the new water has a different temperature from the old water. 

You could also unknowingly alter the pH. It should stay within the 7.5 to 8.5 range.[5] People usually respond to ammonia spikes by performing significant water changes. 

But they don’t realize that large water changes will kill the babies at a faster rate because they cause dangerous fluctuations.

6. Feeding The Fry Adequately

You cannot successfully raise molly fish without providing the proper diet. Protein is the most critical component for a growing molly fry. 

A Virginia State University paper noticed that the demand for protein was highest during the earliest stages of a fish’s life.[6]

However, as the fish matured, the creature’s protein requirements reduced. This explains the advice coming out of the G.B. Pant University of Agriculture and Technology. 

A paper from the college of fisheries science has listed some of the meals a fish requires, including shrimp meal, brine shrimp, and squid meal.[7]

You should give molly fry live organisms like bloodworms and micro worms where possible. Don’t forget to grind the food into tiny pieces the baby mollies can consume. 

You can increase the size of the food particles as the babies mature. In the beginning, they will only eat microscopic organisms. But if you wait a few weeks, the molly offspring will eventually adopt the same diet as their parents.

Make sure you account for their voracious appetites. You can’t feed them two or three times a day. They need at least five meals.

The food goes hand in hand with your filtration. If you don’t have a sufficient filter, the leftovers will overwhelm the nursery, causing an ammonia spike. 

An excellent video that shows how to feed molly fry from day 1.

7. Keeping The Nursery Clean

Maintenance has several dimensions. First of all, you have to change the water once or twice a week, depending on the size of the water change.

Purify the new water with conditioners to eliminate toxins like chlorine and lead. Secondly, you should vacuum the bottom to remove fish poop and leftovers. 

Thirdly, don’t allow dead organisms to linger in the water. Remove the dead plants and animals before they decompose. 

Don’t ignore the filters. Clean them without killing the nitrifying bacteria. This means avoiding chlorinated water. You can’t change the filter media, not completely.

The nitrifying bacteria live in the filter media, and replacing it entirely is the equivalent of undoing the cycling process. 

If you change the filter media without realizing the consequences, you can fix the problem by adding filter media from an established tank.

A molly fish fry, swimming freely in its nursery.

My Recommended Gear For Molly Fry

1. Water Testing & Maintainance

2. Aquarium Equipment

3. Food

4. Fish Tanks

References

  1. https://www.allpondsolutions.co.uk/fishkeeping-advice/where-should-i-place-my-fish-tank.html
  2. https://fishlab.com/location-to-place-fish-tank/
  3. https://theaquariumguide.com/articles/choosing-the-right-freshwater-aquarium-filter
  4. https://buceplant.com/blogs/aquascaping-guides-and-tips/beginners-guide-to-aquarium-filters-and-types-of-filtration
  5. https://modestfish.com/molly-fish-care/
  6. https://fisheries.tamu.edu/files/2019/01/FST-269.pdf
  7. https://www.researchgate.net/publication/354461677_Food_and_Feeding_of_Ornamental_Fishes