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Will Molly Fry Survive In The Main Tank?

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Growing molly fry in the main tank can be tempting. That was the dilemma I had to face a few years back. After all, dedicating an entirely new tank can be cumbersome. Fortunately, over the years, I gained some experience in this field.

Molly fry will rarely survive in the main tank. Ideally, they should be raised in a nursery for roughly two months. After that period, they will enter the fingerling stage and be too large to fit in adult fish’s mouths.

As we move forward, I will discuss when molly fry can be introduced to the main tank. I will also show you what equipment you can use to make this transition smoothly.

A couple of days old molly fry, swimming in a temporary nursery.

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.

Will Molly Fry Survive In The Main Tank?

Most aquarists would prefer to keep their molly fry in the main tank. Nursery tanks are not cheap. You must fit them with the same accessories you find in community tanks, including filters, heaters, and plants.

As such, most aquarists prefer to keep all their fish in one place. Unfortunately, that is not always an option.

Molly fry are a poor fit for main tanks. You have three primary challenges, namely:

1. Predators Can Easily Eat Them

This is your biggest problem. First of all, adult mollies won’t hesitate to eat their offspring. Secondly, the babies are just an easy snack for the other adult fish in the water. They can’t help it.

Even if you replace the inhabitants of your community tank with friendly species, you will lose your babies within a week or two.

You cannot avoid this outcome because adult fish have a habit of eating everything that fits in their mouths. This is why aquarists with overcrowded aquariums place pregnant mollies in the main tank.

They want the adult fish to keep the molly fry population under control. Others breed mollies in community tanks because they want the fry to supplement the diets of the adult fish.

This molly fry is too exposed to predators.

2. They Will Find It Difficult To Eat

Even if the fry survive the predatory instincts of their adult neighbors, the struggle for food will probably kill them. Two factors can cause starvation in an aquarium with seemingly sufficient food:

  • Tank Size

If the tank is too large, the fry will starve because they must cross significant distances to reach the food.

Unfortunately, many aquariums are too large because they have to accommodate adult fish, which have more demands than the fry.

Even if the babies can reach the food, they may die because of all the energy they have to expend to get it.

  • Competition

You cannot expect molly fry to compete for food with their adult neighbors. They will lose every time, especially if you have a sizable population of adult fish. The adults will consume all the food before the babies reach it.

3. Molly Fry Are Sensitive

Molly fry appreciate the same conditions as their parents. You can keep them happy by maintaining the same pH, temperature, and hardness that adult mollies enjoy.

However, baby mollies are more sensitive.[1] As such, their presence will make the task of maintaining a community tank more challenging. They won’t respond well to fluctuations, especially during those first few days.

Dedicated aquarists can keep adult mollies and their offspring alive in the same aquatic space. But the task may overwhelm casual aquarists.

It is worth noting that molly fry are not always a nuisance in the main tank. Yes, they are more challenging to care for in an environment with adult fish.

However, they are also easier to feed. After all, the same meals adult mollies eat will satisfy the babies if you grind them into smaller pieces.

Additionally, baby mollies are harmless. They won’t antagonize or attack their parents in the main tank. That being said, these are minor benefits that don’t justify their presence in the main tank.

Ultimately, they are not as attractive as adult mollies. Therefore, you are better off keeping them in a nursery.

When Can Molly Fry Go With Adult Mollies?

Technically speaking, you can send molly fry to the adult tank whenever you want. However, it is better to wait two months before doing so.

At the age of two months, molly fry enter their fingerling stage. They will reach a size of four to six inches and be too big to fit in adult fish’s mouths.

It is worth mentioning that you can introduce molly fry to adults sooner than that. The key is to take the necessary precautions to keep them safe, including:

1. Plants & Decorations (Recommended)

Give the babies places to hide. That means installing plants and adding some decorations.[2] You don’t have to use bowls, caves, or other elaborate items.

Any object that provides cover will do. Just remember to scrub them thoroughly. Otherwise, you may introduce parasites.

If you don’t have any decorations just yet, I personally recommend the JIH Aquarium Fish Decor Set (link to Amazon). This set contains seven pieces of plastic plants and a cave rock, and fish fry absolutely love them.

Another thing that may help you keep your molly fry alive in a community tank is getting live plants with brushy roots. Molly fry love hiding behind them.

Any of the following will work great in a tank with molly fry:

  • Amazon Frogbit (Limnobium laevigatum)
  • Red Root Floater (Phyllanthus fluitans)
  • Water Lettuce (Pistia stratiotes)
This molly fry is safe because the foliage covers it.

2. Breeder Box (Not Recommended)

Breeder boxes allow baby mollies to remain in the tank. They create a barrier between the fry and their adult counterparts. You can keep female mollies in the breeder box until they push the fry out.

The babies will fall into a bottom compartment where the mother cannot reach them. The fry can stay in the breeder box for the next five weeks until the adult fish are no longer a threat to them.[3]

Breeder boxes are pretty prevalent these days. However, from my experience, it is better to avoid them. The space the fry have is just not enough and causes a lot of stress.

3. Adjusting The Water Parameters

Newcomers do not expect water conditions to affect a molly fry’s survival ability in a community tank. They forget that water conditions can influence an adult molly’s temperament.

You can improve a baby molly’s chances of surviving in a community tank by removing the hostile fish. But if the conditions are wrong, the friendly fish you left behind will become aggressive.

They will respond to the stress by hunting and eating the baby mollies, not to mention any other vulnerable creature they encounter. Therefore, you have to maintain the appropriate conditions.

Aim for these water parameters while performing weekly water changes of roughly 30 percent:

  • 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 recommend getting the API Water Test Kit (link to Amazon). This one is pretty reliable and lasts for about eight hundred measures.

You may find more useful information in this article, where I discussed what equipment molly fry need (including my personal recommendations for a heater, a filter, an air stone, etc.).

4. Feeding The Fish Properly

This goes without saying. If you give the adult mollies sufficient food, they are less likely to harass their offspring. On the other hand, starved adults won’t hesitate to eat the babies.

Also, bear in mind that adult fish and fish fry have different requirements when it comes to food. That is another reason why raising the fry in a nursery is a better option.

As I discussed in my molly fry feeding guide, these creatures can eat up to five times a day. On the other hand, adult fish eat merely two to three times a day.

A young molly fish fry, searching for food on driftwood.

Are Two Months Always Enough?

Molly fry cannot survive in the main tank because filial cannibalism is common among fish.[4] Fish have a reputation for eating anything that fits in their mouths.

For that reason, you have to wait until the babies are too big for the adult fish to swallow. The size is the key.

Some aquarists will tell you to wait one or two months.[5] But that may vary depending on the particular fish you have in your aquarium.

Also, that number isn’t entirely accurate. At two months, the mollies are usually too big for an ordinary adult molly fish to eat. But what if your fry’s growth is stunted?

What if the baby molly has a genetic anomaly that has prevented the creature from attaining the appropriate size within those first two months? The adults will swallow the molly fry whole.

For that reason, you cannot base your decisions on the duration. Yes, it makes logical sense to introduce the babies to the community aquarium after a month or two.

But don’t be afraid to keep the fry in the nursery if the creatures are still too small by that point.

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

Conclusions

Molly fry shouldn’t go with adults immediately. They won’t survive in the main tank as they are too small and will quickly be eaten by their adult counterparts.

Ideally, it is best to raise the baby mollies in a nursery for about two months. After this period, they will enter their fingerling stage and won’t fit in adult fish’s mouths.

You can try raising them with adults if you don’t have a spare tank. However, it is essential to introduce dense foliage and a sufficient amount of hiding spots.

References

  1. https://fishkeepingguide.net/molly-fish/can-molly-fry-survive-in-main-tank/
  2. https://urbanfishkeeping.com/will-cichlid-fry-survive-in-a-community-tank/
  3. https://www.aquariumcoop.com/blogs/aquarium/breeder-box
  4. https://www.sciencedaily.com/releases/2016/02/160210111907.htm
  5. https://www.wikihow.com/Take-Care-of-Molly-Fry