Why Are My Fish Not Eating?

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?

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.

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.

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.

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.

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.


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.

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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.