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Do Mollies Eat Their Babies? (With Prevention Tips)

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When I realized my molly fish was pregnant, I got pretty excited. But I wasn’t sure what would happen after the fish gave birth. Will it eat the babies, or can they coexist in the same tank? Luckily, as time passed, I gained some experience in this field.

As opportunistic eaters, molly fish will eat whatever fits in their mouths, including their babies. That habit becomes more prominent when the molly fish are stressed, most commonly due to inappropriate water conditions, an overcrowded environment, and lack of food.

As we move forward, I will elaborate on whether molly fish are likely to eat their babies. I will also discuss the factors that may cause that and what steps you should take to prevent this from happening.

Do Mollies Eat Their Babies?

Yes, mollies eat their babies. It is unfortunate but true. This is why aquarists place pregnant mollies in separate tanks and breeding boxes.

The goal is for the pregnant mollies to give birth in the absence of other adult fish that may eat the babies before they are large enough to defend themselves.

But once the molly fish gives birth, aquarists will send it back to the community tank, allowing the fry to live alone. If you’ve never reared pregnant molly fish, this is what you should know about their behavior:

1. Why Mollies Eat Their Babies?

Mollies are not cruel. They don’t eat their babies out of malice. Instead, they are opportunistic feeders.[1] Like most other fish; they will eat whatever they can fit in their mouths. 

To the untrained eyes of a molly fish, the babies are no different from food pellets. The creature will gobble them up without a second thought. Interestingly enough, this isn’t unique to livebearers like mollies. 

Egg layers can eat their young ones as well. Though, livebearers have an advantage. Live babies have a higher mortality rate than fish eggs and the fry that hatch from them. Not only are live babies larger than hatched fry, but, unlike eggs, they can swim away from danger.[2]

Additionally, livebearers can protect their eggs from predators by keeping them inside their bodies until they hatch, a benefit that egg layers do not enjoy.

Admittedly, this practice puts the livebearer at risk. Housing the eggs in its body weakens the animal because it diverts resources to the fry. In the case of fish, the mollies will still eat the same fry they protected from predators by allowing them to gestate in the womb.

Experts call this habit ‘Filial Cannibalism.’ They don’t buy the idea that filial cannibalism occurs because the babies are an easy meal.[3] Some argue that fish parents eat their offspring when it ‘Maximizes their lifetime reproductive success.’.[4]

2. Does The Temperament Matter?

The temperament doesn’t play a role in this situation. People expect cichlids to eat their young ones because they are so violent. In that same regard, they expect peaceful livebearers to coexist with their offspring.

But that is not true. Molly fish are peaceful.[5] They can live in harmony with other peaceful fish. However, that friendly temperament won’t keep them from eating their offspring.

As was noted earlier, mollies are not malicious. They eat their babies because they confuse the fry for food. Their temperament doesn’t drive their actions, and neither can it prevent them from eating their babies. They will do the same thing to adult fish with small bodies.

For instance, nano species like the Indonesian Superdwarf fish may not survive a molly fish tank. After all, they have a maximum size of 0.41 inches.[6] A 5-inch molly will eat them. 

3. Does The Molly Type Matter?

You can’t save your fry by changing the type of molly fish. Most mollies have similar temperaments. Some varieties, such as Dalmatian and Lyretail mollies, will manifest aggressive tendencies if you provoke them.

But most of them tend to display the same peaceful mannerisms. And again, those peaceful mannerisms won’t stop them from eating their offspring.

4. Do The Conditions Matter?

A molly’s peaceful temperament won’t keep it from eating its young. However, an aggressive molly is more likely to eat its offspring than a peaceful fish. 

A peaceful molly will eat any babies it comes across that are small enough to fit in its mouth. An aggressive molly may hunt its offspring down before eating them. Even though mollies are peaceful, the wrong conditions can compel them to lash out.

Check your parameters. Is the temperature too high? What about the pH? How many fish do you have in the tank? Are the mollies overcrowded? If you have a clean tank with the correct parameters, what is the ratio of male-female mollies?

You need two to three female mollies for every male molly. Otherwise, the male mollies will fight one another. Molly fish are less likely to eat their fry in a clean, sizable, well-maintained tank with an appropriate quantity of female fish.

Will The Mollies Eat Their Babies Immediately?

The chances of a molly fish eating its young ones as it pops them out are very low. It is possible but unlikely. Pregnancy in mollies is stressful. This is why pregnant mollies are so sluggish.

As mollies are about to give birth, some of them will stop moving altogether. Like humans, some mollies will die during the birthing process. Though, most of the time, death occurs because of complications such as the fry getting stuck in the birth canal.

You can make things worse by forcing the fish to give birth in poor conditions. But even in the best of situations, the birthing process is stressful for livebearers like mollies and guppies. 

That is why many aquarists are hesitant to move the female molly back to the community tank once it gives birth. Instead, they will place it in a separate container for one or two days, allowing the creature to recover before returning it to the community tank. 

The fish needs a break before it returns to its routine. Yet, this doesn’t apply to every single fish. Some mollies will return to their everyday lives when they push the last fry out. But even in those circumstances, the molly won’t attack the fry immediately.

It may take a while for the female molly’s appetite to recover after it gives birth. The abundance of food makes a difference. If your tank has plenty of food, it may distract the mother.

It will eat the babies if it accidentally stumbles across them. But it won’t deliberately hunt them down. Don’t expect hungry mollies to behave. They will eat whatever they can find. 

When Are The Molly Fry Safe?

You don’t have to separate the female molly from its babies. You can protect the offspring by adding plants. An aggressive fish will hunt the fry down all the same. But that behavior won’t last forever.

After one or two months, the babies will grow to a size where their mother can no longer eat them. At this stage, you can move them to the community aquarium.

How Do I Prevent Mollies From Eating Their Babies?

As noted earlier, molly fish will eat anything that fits in their mouths, including their own babies. However, there are some ways to increase the survival rate of the fry. First, you can use an aquarium divider.

By placing a divider, the fry can easily escape to the other side of the tank as soon as they are born. The adult molly, however, will be too large to cross to the other side. Here is a helpful Youtube video that will show you how to do that:

I also suggest that you adjust the water parameter. Keeping them within the desired range will lower aggression, including towards the newborns. These are the water parameters I suggest you aim for:

  • Temperature: 77-80 degrees F (25-27 degrees C) 
  • pH: 6.7 and 8.5 
  • Hardness: 20-30 KH 
  • Ammonia & Nitrites: 0 ppm 
  • Nitrates: <20 ppm

To measure the pH, nitrates, nitrites, and ammonia, I personally use the API Water Test Kit (link to Amazon). That bundle is highly accurate and easy to use. It also lasts for about eight hundred measures, so it’s pretty cost-effective.

Ultimately, I suggest that you feed your molly properly as it starts giving birth. I’ve previously discussed that one of the late signs of a pregnant molly is the lack of interest in food. But once they start eating again, it is best that they’ll be distracted with food.

Conclusions

Mollies will eat their babies after they have done giving birth. That doesn’t happen immediately, as the fish is vulnerable and exhausted. However, if kept in the same environment, the parents will ultimately eat their fry.

In order to avoid this, it is best to install an aquarium divider. That will allow the fry to escape to the other side of the tank. I also suggest that you keep the water parameters within the desired range so that the parents remain calm in the meanwhile.

Still curious? Feel free to check my complete guide on pregnant molly fish. There, I discussed how to care for pregnant mollies, how long they remain pregnant, how to identify signs of pregnancy, and a lot more.

References

  1. https://www.fishkeepingworld.com/faq/do-mollies-eat-their-babies/
  2. https://en.wikipedia.org/wiki/Livebearers
  3. https://www.livescience.com/2053-animals-eat-offspring.html
  4. https://www.sciencedirect.com/science/article/abs/pii/016953479290190M
  5. https://www.fishkeepingworld.com/molly-fish/
  6. https://aquanswers.com/smallest-freshwater-aquarium-fish-nano-species-stay-small-micro-tank/