Why Is My Molly Fish Not Eating? (With 6 Quick Solutions)

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It can be worrisome when you find a fish in your aquarium that doesn’t seem to be eating anything. I remember how frustrated I was when my molly fish did not eat, regardless of the choices I offered it. Luckily, as time passed, I learned why this might happen and how to deal with the issue.

Molly fish usually do not eat when they are stressed. That can be secondary to inappropriate water conditions, including pH, temperature, and ammonia. However, some mollies will refuse to eat because they are constipated, or carrying a disease, such as dropsy, swim bladder disease, and infections.

As we move forward, I will discuss each of these and provide some valuable ways to bring back your molly’s appetite. If you are in a rush, I will say now that the first step would be testing the water parameters using the API Aquarium Test Kit (link to Amazon).

Why Is My Molly Fish Not Eating?

Fish are always responsive to food. They are not necessarily hungry, but they want to eat, all the same. They can choose to stop eating on occasion for a variety of reasons. However, they should react to food whenever you add it to their tank.

If your mollies show no interest in food, you should investigate quickly before the ailment responsible for their behavior kills them. Some potential causes that you should investigate include:

1. Your Molly Is Constipated

Constipation is a common occurrence in fish. It has multiple causes; one of the most prominent is overfeeding.[1] Though, some people attract this ailment by purchasing poor-quality food items. If the quality isn’t to blame, the feeding method is probably at fault.

Some dry foods will expand in your molly’s stomach later on, blocking the digestive tract. You have to submerge them beforehand. A molly fish with constipation will either eat little or no food.

You can tell that your molly fish is constipated by its behavior. If a molly swims slowly, is bloated, or hides in the bottom of the tank, it’s likely suffering from this ailment. It will be mostly immobile and have difficulty swimming.

Also Read: Molly Fish Constipation

2. The Molly Is Sick

Molly fish are susceptible to numerous diseases, parasites, and infections. Human beings lose their appetite when they fall sick, and fish are no different. Some of the illnesses they contract can steal their desire for food.

However, it would help if you weren’t so quick to assume that your fish are sick unless you have identified additional signs of ill health. For instance, erratic swimming can point to swim bladder disease and dropsy.[2]

Parasites will drive the creatures to rub their bodies against surfaces in the aquarium. Fin rot will produce frayed fins in mollies. The presence of fuzzy growths is usually a sign of fungal or bacterial infections. If they have Pop Eye, their eyes will bulge.

Loss of appetite is normally one symptom among many that manifest when a molly fish is sick. If you can use those other symptoms to identify the disease ailing your mollies, you can find the source of the molly’s loss of appetite.

3. Low Water Quality

Molly fish should be kept in a properly cycled tank that has the appropriate conditions. You have to keep the pH, temperature, and hardness in the acceptable range. In the second section of this article, I will show you how to do that.

If the mollies are not eating, more often than not, the quality of their water has fallen. Either the parameters have changed, or the tank has dangerous levels of ammonia, nitrates, chlorine, copper, and various other toxins.[3]

Toxins typically skyrocket in poorly maintained tanks with dirty water that has been polluted by fish waste and leftovers. If you’ve taken steps to clean the tank, but the mollies are even worse, the changes you made were too drastic. 

More than likely, the mollies spent too much time in the dirty water. While they were far from happy, they grew accustomed to the conditions. By suddenly altering the environment, you probably induced stress in the creatures, making them even less likely to eat.

Also Read: Stress In Molly Fish

4. New Environment

Mollies that are new to a tank are more likely to go into hiding. This is because they are not accustomed to their new environment. For this reason, they will manifest all the common signs of stress, including a loss of appetite.[4]

Such behavior in new fish isn’t a problem. If all the conditions in the aquarium are appropriate, you have to wait for the creatures to grow accustomed to their surroundings.

5. The Wrong Water Temperature

The wrong temperature isn’t just a source of stress. When the water is too cold, a fish’s metabolism drops.[5] The fish slows down, becoming lethargic. Not only does it spend more time sitting in one place, but it doesn’t eat as much. It may stop eating altogether.

Water that is too hot isn’t any better because it causes oxygen deficiencies. Mollies in oxygen-deficient tanks are just as disinterested in food. They will stop eating regardless of the quality of food they are given.

Also Read: Molly Fish Temperature

6. Your Molly Is Pregnant

Pregnancy makes mollies lethargic. This is why they spend so little time swimming. Some pregnant mollies spend their days lying still on the substrate. In many cases, they won’t eat as much as they usually do. In extreme situations, they may stop eating. 

Also Read: Pregnant Molly Fish 101

What Do You Do If Your Molly Fish Is Not Eating?

If your mollies have stopped eating, your only option is to identify and eliminate the factors causing their behavior. You can use the following steps and avenues:

Step 1: Adjusting The Environment

Make sure the tank is in the best possible condition. That means making adjustments to the temperature (72 to 78 degrees F), pH (7.5 to 8.5), and hardness (15 to 30dGH) to keep them within the appropriate range.[6]

I use the API Aquarium Test Kit (link to Amazon) to measure the pH, ammonia, nitrates, and nitrites in my tank. That bundle is highly cost-effective and easy to use. It comes with a chart and comprehensive instructions to help you identify the problems in your tank.

A well-maintained tank that has the correct parameters isn’t simply comfortable. A conducive environment will expedite a sick molly’s healing process. If they are sick, keeping the proper water parameters will help them combat diseases.

For the water temperature, I use the Cobalt Aquatics Neo-Therm Pro Aquarium Heater (link to Amazon). That is the only device in my tank that keeps the temperature stable. I’ve tried other devices, but it is the only one that works well for me.

Also Read: Molly Fish Bullying & Attacking Other Fish

Step 2: Routine Maintenance

You should perform regular water changes to keep the tank clean. Naturally, you need an efficient filtration system whose strength matches the size of your tank. But a powerful filter isn’t enough. 

It may remove debris, but you can’t trust it to keep the concentration of toxins like ammonia down. As a rule of thumb, it is best to replace 15 to 20 percent of the water weekly. That will prevent abrupt changes in the water chemistry.

You can’t rely on conditioners either. Yes, they are designed to neutralize toxins like ammonia and chlorine. But they are supposed to accompany weekly water changes. You use them to treat the new water added during a water change, but they cannot replace water changes. 

People that forget to perform regular water changes also forget to clean their tanks. Water changes cannot remove the dirt and grime on your tank’s walls and decorations. You have to scrub them off. Otherwise, they will make your water dirty.

Also Read: Molly Fish Tank Setup

Step 3: Adding A Few Plants

Mollies should be kept in a planted tank because the plants provide hiding places. You can also add other decorative items. Hiding places are important because they combat stress, especially in mollies that have to live in tanks with large and violent fish. In fact, the absence of hiding places can increase the stress in a molly fish, ruining its appetite in the process.

Also Read: 11 Plants Your Molly Fish Will Love In Their Tank

Step 4: Picking The Right Number Of Mollies

I like keeping one molly fish for every ten gallons of water. It is crucial to remember that mollies are schooling fish. They have a peaceful and social temperament that allows them to thrive in groups. 

The more mollies you have, the more confident and secure they will feel, the easier it will become for them to escape the side effects of stress. This is particularly helpful for mollies that live with hostile fish. Also, your school should have more females than males. Otherwise, the males will harass the females.

Step 5: Choosing The Right Tank Mates

Speaking of hostile fish, you can make life a lot easier for your mollies by keeping them in tanks with harlequin rasbora, plecos, corydoras, zebra danios, and other suitable tankmates that are less likely to act aggressively towards them.

Even if your molly’s tankmates are peaceful, you are still expected to add plants and decorations. The hiding places enhance the molly’s peace of mind, regardless of whether or not they have predators to hide from.

Also Read: 19 Great Neon Tetra Tank Mates

Step 6: Dealing With Disease & Constipation

Sometimes, you can fight an illness or infection by simply changing the water. But on many occasions, you have to take more direct action. You can fight some diseases by raising the temperature by a few degrees, with the most prominent example being ich. 

Some ailments, such as fungal infections and fin rot, compel aquarists to quarantine the sick fish in hospital tanks to be treated with antifungal drugs without affecting the healthy mollies. Either way, I suggest consulting a vet.

Constipated mollies require fasting as well as a special diet. For instance, you can feed constipated mollies peeled and cooked peas to fight swim bladder disease. Here is a helpful Youtube video that describes how to do that:

Also Read: 15 Molly Fish Diseases & Their Treatments

How Long Can Mollies Go Without Food?

Adult mollies can go two weeks without food. However, molly fry are not as tolerant; the longest they can survive without food is three days. The conditions in the tank also matter. Mollies in a well-maintained aquarium can last longer without food because they are healthier and less stressed.

This is why aquarists who have to go on long trips are encouraged to clean their aquarium and perform water changes. A clean aquarium gives molly fish, both adults, and fry, the best chance of survival.

Also Read: How Often To Feed Molly Fish

What Is The Best Food For Mollies That Refuse To Eat?

If your molly hasn’t eaten for a long time, it is best to feed it a diet that has the highest possible protein level. This helps strengthen its immune system. My first choice would be bloodworms since they have a high protein content, and most mollies love eating them.

I like keeping bloodworms frozen, so I don’t have to worry about them going bad while I’m away. The bloodworms come in handy whenever my mollies are not eating. But if you’d rather use fresh worms, you can go for it.

Another option is lettuce. Like bloodworms, lettuce has a high protein level. That makes it an excellent supplementary food source for struggling mollies. True to form, my mollies love eating it. I prefer feeding them iceberg lettuce because I like how its bright white color contrasts their black bodies.

If your mollies don’t eat bloodworms or lettuce, you can try daphnia, brine shrimp, and even beef heart as alternatives. Be sure to pick the appropriate diet for the right age and stage in their development.

Also Read: What Do Molly Fish Eat?


Lethargy and a loss of appetite are two of the most common symptoms that mark fish as sick. But lethargy and a lack of appetite can have multiple causes. We covered the most common ones in this article. I also explained how to deal with them.

If you have a molly that is not eating, my suggestion is to fix the problem in the tank before starting any treatment. Mollies cannot survive long without food, especially infant mollies. If you are merely starting, I suggest testing the water chemistry and temperature.


  1. https://www.ratemyfishtank.com/blog/constipationindigestion-in-aquarium-fish
  2. https://molliesfish.com/molly-fish-diseases-and-treatments/
  3. https://www.mypetwarehouse.com.au/my-pet-blog/pet-care/fish/why-is-my-fish-not-eating
  4. https://www.animalwised.com/why-are-my-fish-not-eating-744.html
  5. https://fishkeepingforever.com/why-are-your-fish-not-eating-9-possible-reasons/
  6. https://www.theaquariumguide.com/articles/mollies-care-guide