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Molly Fry Growth Stages: A Full Guide With Pictures

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Many fish owners are impatient and cannot wait for their molly fry to grow. That is at least how I felt when I first grew these wonderful creatures. Besides, I wanted to understand the molly fry growth stages to know if my fish are having developmental problems.

These are the molly fry growth stages:

  • Stage 1 (days 1-30) – The fry are fully transparent and extremely vulnerable. 
  • Stage 2 (days 30-60) – The reproductive organs are first revealed.
  • Stage 3 (months 2-4) – The mollies are sexually mature and show vibrant colors. 
  • Stage 4 (months 4-6) – The mollies are considered adults and stop growing.

As we move forward, I will share some detailed pictures demonstrating the different molly fry growth stages. Then, I will provide a few useful tips to ensure your fry grow healthy and at the right pace.

A couple of days old molly fry, captured with a mystery snail.

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 Are The Molly Fry Growth Stages?

Molly fish can give birth every 60 days. The creatures will transition through three significant stages before reaching adulthood, namely:

Stage 1: Fry (Days 1-30)

This is where every molly fish starts. Mollies give birth to live babies just half an inch in size. Mollies are at their most vulnerable here, which is why aquarists send the mothers back to the main tank.

If you don’t, the female fish will eat her offspring. The babies will remain in this state for about a month before entering the juvenile stage.

As I discussed in another article, on average, fifty percent of molly fry don’t survive. Unfortunately, those mollies that don’t reach adulthood die during this stage.

Stage 2: Juvenile (Days 30-60)

The fry will enter the juvenile stage within four weeks. Initially indistinguishable from transparent tadpoles, you can expect the creatures to develop more distinct features at this point.

At the very least, the presence of a gravid spot or gonopodium will set the babies apart as either male or female. You may even notice the colors.

A juvenile male molly fish, first showing its gonopodium.

Stage 3: Fingerling (Months 2-4)

Mollies will reach their maximum size at this stage (4 – 6 inches). People use the term ‘Fingerling’ to refer to babies in this state because the fry are the size of a finger, more or less.[1]

It isn’t an exaggeration to call fingerlings teenagers. You can start placing the genders in separate tanks to prevent breeding. This assumes that you want to avoid breeding.

Fingerlings can survive in an adult tank because they are too large to fit in the mouths of adult mollies. Although, you should surround them with plants and decorations to be on the safe side.

Yes, fingerlings are too large to fit in the mouths of adult mollies. But adult mollies can still bully their smaller counterparts to death. 

The species is peaceful. However, the wrong conditions can incite aggression in the friendliest of fish.

Stage 4: Adult (Months 4-6)

Mollies are adults at four months.[2] At this stage, they can live comfortably in a community tank. They can also eat the same foods as their parents.

Mollies aren’t likely to grow noticeably beyond this stage. If they do grow, the changes are minor.

While most mollies reach sexual maturity at the fingerling stage, by the time they are adults, all mollies can reproduce. If they don’t, they are probably genetically deformed and will remain sterile.

How Do You Make Baby Molly Fry Grow Faster?

Mollies will reach their full size within four months, but that is not guaranteed. Some mollies will stagnate in their growth because of various factors, including inadequate water changes and a poor diet.

Therefore, you have to take the following steps to boost a baby molly’s growth rate:

1. Keeping The Right Water Parameters

People expect a fish’s size to fit the tank it inhabits, but fish cannot control their size. They can’t accelerate or decelerate their rate of growth, not intentionally. However, they can become stunted if you expose them to water with the wrong parameters.

But that stagnation occurs because of the stress and diseases that haunt molly fry in a poorly maintained tank, not because they have chosen to slow their growth.

You can overcome these limitations by adjusting the parameters in the tank. Try aiming for these water parameters:

  • 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

Eighty degrees F is warmer than some people expect. However, warm water is good because it boosts metabolism, which, in turn, compels the babies to eat more food. The more food baby mollies eat, the faster they grow.[3]

Baby mollies also require roughly 12 hours of light every day. Like their parents, they need darkness to sleep. Keeping the lights on 24 hours a day will kill them.

To measure the ammonia, pH, nitrate, and nitrite, I use the API Water Test Kit (link to Amazon). This one is a bit more expensive than average, although it is extremely reliable and lasts for hundreds of measures. 

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

A molly fish fry, swimming at the top of the tank.

2. Picking The Proper Tank Size

Adjusting the tank size is a crucial step in keeping molly fry alive. One study found that fish raised in smaller tanks were less likely to take risks.[4]

Admittedly, risk-taking behavior doesn’t really matter to aquarists where molly fry are concerned. They are more interested in a fry’s wellbeing, and unfortunately, small tanks will compromise the health of your babies.

You should give them 5-20 gallons of water.[5] However; you shouldn’t go overboard. Newborn fry are tiny and cannot survive in massive tanks.

That is because they won’t be able to reach the food. They do not have the strength to traverse large aquariums in search of sustenance. 

They will either starve to death or succumb to stress and exhaustion. Therefore, you have to find a balance. The biggest tank is not necessarily the best option.

3. Aquarium Maintainance & Water Changes

As a rule of thumb, change 15 to 20 percent of the water every week. Molly fry eat multiple meals a day. That shouldn’t come as a surprise since they are still growing. 

Therefore, their nutritional needs are significant. However, you run the risk of saturating the water with leftovers.

Additionally, mollies can produce up to 100 babies. The waste they generate will sink to the bottom, where it will rot unless you remove it.

Water changes are the most important tool in your arsenal. However, you cannot boost a molly fry’s growth with water changes alone. You need proper filtration.

The filter can’t be so strong that it sucks the babies in. You should invest in attachments that prevent this eventuality. 

However, the filter can’t be so weak that it allows pollutants to persist in the water. Again, like the tank size, you have to find a balance.

If you are looking for a filter for your molly fry tank, I personally recommend the Lefunpets Sponge Filter (link to Amazon). It has the precise intensity molly fry need. It is also built in a way ensuring it won’t suck the fry.

A molly fry nursery that contains roughly 100 molly fry.

4. Feeding The Molly Fry Properly

Molly fry require nutritious meals that include daphnia, vinegar eels, bloodworms, egg yolk, zucchini, carrots, and more. Prioritize protein-rich items.

It is also essential to adjust the feeding schedule. Up until the juvenile stage, molly fry should eat five times a day in consistent intervals.

If you don’t have any experience in this area, feel free to check this article, where I explained everything you need to know about molly fry food.

When Do Molly Fry Get Their Color?

It depends on the fish. Most mollies will manifest distinct colors within two months (when entering the fingerling stage). Those colors will become more vivid and vibrant in the following months.

But don’t be surprised if your molly’s colors remain muted and unimpressive for the first few months. Some fish have genetic anomalies that prevent their colors from showing within the expected period.

You also have cases where poor conditions, such as high temperatures and ammonia poisoning, steal a molly’s color. Many aquarists do not realize that muted or absent colors are symptoms of stress and disease.

A paper in the Journal of Veterinary Medicine and Animal Sciences noticed that aquarists could use dietary elements such as spirulina and beetroot to enhance a fish’s colors.[6]

Although, many professional aquarists have found that it is much easier to rely on colorful lights and backgrounds.

A detailed video showing the molly fry development, day by day.

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

Conclusions

Between days 1 and 30, the newborn mollies are at the fry stage. They will barely have any colors except for their internal organs. That is their most vulnerable stage in which many of them will die.

After a month, the molly fry will enter its juvenile stage. You will be able to tell if it’s a female or a male molly at this point, as the fry develops a gravid spot or a gonopodium, respectively.

At the age of two months, the juvenile mollies enter the fingerling stage. Some aquarists name it the teenage stage. Either way, at this point, the mollies are ready to reproduce.

After four months, the mollies are considered grown adults. They will barely change at this point, and if they do, the changes will be minimal.

References

  1. https://www.fao.org/3/ac381e/AC381E02.htm
  2. https://www.itsafishthing.com/how-big-do-mollies-get/
  3. https://www.aquariumnexus.com/molly-fish-fry-care/
  4. https://www.sciencedirect.com/science/article/abs/pii/S0003347216000889
  5. https://www.wikihow.com/Take-Care-of-Molly-Fry
  6. https://meddocsonline.org/journal-of-veterinary-medicine-and-animal-sciences/Effect-of-chosen-artificial-fish-feeds-on-the-growth-rate-of-the-black-molly-Poecilia-sphenops.pdf