Other health problems

Why Are My Fish Not Eating?

Josie F. Turner
By Josie F. Turner, Journalist specialized in Animal Welfare. May 16, 2017
Why Are My Fish Not Eating?

Fish are incredibly sensitive animals. Seeing your fish not eating is very worrying, especially if you are new to having fish and do not know why it is happening.

There are several reasons that could explain why your fish has stopped eating, and sometimes they are minor causes. Other times the reasons are serious and you need to take them to the vet or take immediate action.

Keep reading this AnimalWised article to find out the main reasons that answer your question: Why are my fish not eating?

You may also be interested in: Why Is My Cat Not Eating and Drinking?
  1. New fish
  2. Inadequate temperature
  3. A dirty aquarium
  4. Incorrect lighting
  5. Water hardness and pH
  6. Diseases
  7. Territoriality

New fish

Sometimes, when you get a fish and put them in their aquarium, you will notice they refuse to eat. This happens because they are under stress, due to the large and abrupt change in their environment. This reaction is normal and usually resolves by itself when the new inhabitant of the aquarium acclimatizes to its new habitat.

If you find that after a few hours they are still not eating, perhaps the problem is due to an deficiency in the aquarium. You could have also made the mistake of choosing a species unsuited to your microclimate.

Why Are My Fish Not Eating? - New fish

Inadequate temperature

If your fish suddenly stops eating, it is often because, for some reason, the correct temperature has dropped in the aquarium. When this happens they will go into dormancy.

Before getting any new fish, you must know the temperature range required by the species you choose. Do not purchase one that is incompatible with the temperature set in your aquarium.

Why Are My Fish Not Eating? - Inadequate temperature

A dirty aquarium

If you don't keep their tank clean, the water becomes visibly degraded. When the water is not changed weekly, which is recommended for proper maintenance, it increases the level of nitrates and the oxygen level decreases. This causes an imbalance in the aquarium's environment making it uncomfortable for its inhabitants. The fish will often stop eating to prevent their home becoming more dirty.

Why Are My Fish Not Eating? - A dirty aquarium

Incorrect lighting

Sometimes, the fluorescent tube that illuminates the aquarium breaks or melts. At the same time, you will also see that some fish stop eating. Some fish only feed in daylight, and a failing light source confuses them and prevents them from eating properly.

You should always have to hand a few necessary parts in order to make the appliances function properly: a heater, filters, and lighting devices are essential so that any failures can be corrected immediately. On the other hand you should monitor all the parameters of the aquarium on a daily basis.

Why Are My Fish Not Eating? - Incorrect lighting

Water hardness and pH

The acidity and hardness of the water must be optimum so that your aquarium fish are comfortable. If any of these parameters deviate, it is very likely that the discomfort will prevent the fish from eating properly.

If there are faults on important parameters such as pH and water hardness, the life of the aquarium inhabitants will be at risk. That's why the hardness and acidity of the water should be monitored on a daily basis. There are chemicals that can immediately correct these deviations.


If your aquarium runs like clockwork and your fish stop eating, it is most likely the symptom of a disease.

You must check the overall appearance of your fish every day. If you notice one that seems ill, you will have to separate it immediately, put it in a separate tank and go to the vet. If you don't separate them in this way, general contagion is very possible. There are drugs which are diluted in water to improve their overall health in the case of an epidemic.

Why Are My Fish Not Eating? - Diseases


When your fish matures into an adult, they begin to show their hierarchy and territoriality. Alpha males are aggressive and prevent others from feeding if the aquarium is not big enough, and the rest of the fish do not have enough space to live.

When fish grow you have to adjust the number in the aquarium to their current needs. A crowded aquarium causes aggressiveness of alpha specimens of each species. This stresses the others so much that it causes them to die.

Why Are My Fish Not Eating? - Territoriality

Perhaps you may be interested in...

Coldwater Fish tanks
Fish for a Community Aquarium

This article is purely informative. AnimalWised does not have the authority to prescribe any veterinary treatment or create a diagnosis. We invite you to take your pet to the veterinarian if they are suffering from any condition or pain.

If you want to read similar articles to Why Are My Fish Not Eating?, we recommend you visit our Other health problems category.

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What did you think of this article?
my fish did eat but not immeadiently reacting to food
My Betta fish was doing so well and now he is not eating anymore! Everything is still the same but he never eats anymore but he seems fine what should I do?!
clean his bowl
Past 1 week my fish is not eating...I grooming it in one small bowl...15 days it was very active...after tat only it is behaving like this..and anytime it is simply sleeping.....under the bowl.....I don't know what happening for him..anyone can help me to live my fish.. but while I disturbed it then it is more active....
While away for work, my wife overdosed algecide and killed all my fish except for my cat fish. He has recovered and have changed 25g out of 36g of the water. The tank looks a bit cloudy, which I can't fix yet. I have recently tried buying a couple new fish, 2x white skirt tetras and a firemouth. They look healthy and can't see anything wrong, but none of them seem interested in eating. I have tried shrimp, flakes and some worms.
You should to a 100% water change and then do a deep cleaning of everything to make sure everything is clean.
Bilal Ahmed
I have two pairs of blueline shark.
and they are 2 years old.
the acquarium became too small for them thats why i transferred them to a new big tank and since then they are not eating food ...
please tell me the reasons why they not having food.
Administrador AnimalWised
Hi Bilal,

While blueline shark are popular fish to be kept as pets, they are also notoriously difficult to care for. We are glad you are keeping them in pairs, but they really thrive in larger schools. This means a bigger tank, but even then they can become stressed easily. Their poor eyesight means movements in the room where their tank is located can cause stress.

There are other reasons detailed in the article, but it is possible stress is a major factor. Reducing this stress any way you can is the best way to help them eat more, but it may be difficult depending on your resources.
My goldfish has developed red colour on both sides and it has stopped eating. What should i do
snap a pic and send to pets at home
Viresh Mehrotra
Since more then a week one of my fish stopped eating. M warried.tell me d remedy.
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Why Are My Fish Not Eating?