Why Is My Fish Not Eating?

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As every aquarist knows, to correctly maintain and keep fish, you have to make them feel as comfortable in their tank as possible. This usually means replicating their natural habitat by providing them with their preferred lighting and water parameters, enough space to freely grow and move about, and their favorite foods.

But when you notice your fish food still floating at the top of the tank or sinking down to the murky bottom without being eaten, this can be concerning. “Why won’t my fish eat?” you might be wondering. Is there something wrong with them? Is it the food or their health?

Let’s take a look at what to do if your fish is not eating and why they might be refusing to eat. Then, you can better approach their condition and return them to good health.

Why Is My Fish Not Eating?

Loss of appetite in fish can be due to a wide variety of factors. Luckily, most of these issues are easy to remedy, before any long-term consequences can impact your fish tank.

Environmental Issues

Bad Water Quality

Bad water quality is one of the most common reasons fish suddenly stop eating. All fish are sensitive to abrupt changes in the pH or chemicals found in their water, no matter how hardy of a species you keep. In fact, you should never change anything in an aquarium too quickly, as this can stress out your fish.

Fish do just about everything in the water, so it’s very important that you regularly test their water parameters and change at least 10 to 15 percent of their tank water every week.

Fish not eating

Temperature Changes

Fish can’t regulate their own body temperature like humans can, so they rely on you to keep their tanks at the optimal temperature for them.

Most freshwater or reef fish thrive in water temperatures between 74 to 80 degrees Fahrenheit (or 23 to 26.5 degrees Celsius). If the tank becomes any colder than this, your fish may grow sluggish or move more slowly than normal. This can slow down their metabolism and make them feel full when they really should eat, leading to unintentional starvation.

If your fish tank is too hot, on the other hand, your fish could become hyperactive. This might not sound like such a bad thing, but it’s actually worse for your fish than swimming around in cold water.Why is my fish not eating

Fish need to breathe oxygen as much as people do, and unfortunately, the hotter the water becomes, the less oxygen your fish will be able to properly absorb. As a result, they will become more stressed when they find that they can’t breathe.

This stress can cause them to stop eating for a while, so you need to always make sure that their tanks are at the optimal temperature for their species.

New Environment

A fish that is introduced to a new aquarium may not eat right away due to the stress of a new environment. This is a perfectly normal reaction. Fish will usually calm down after getting used to their tank and will start eating again in a few hours.

Part of this acclimation process includes finding spots around the aquarium for them to hide in. Aquatic caves and dense vegetation are the best decorations you can use for this. These spaces can make them feel safe and protected, as well as provide them with cozy places to sleep in.

If you find that your fish still isn’t eating after a few hours, then there might be something else wrong.

Medical Conditions


Pregnant fish may stop eating their normal amount right before they lay their fry. If this is the case, you need to move this fish to a separate, secure breeding tank to make sure they aren’t disturbed as they reproduce.

For most species, you will know if your fish is pregnant if they appear to have a swollen abdomen and a dark triangular marking going toward their lower fin.


If your fish is sick, they might not feel up for eating. If they display these other symptoms, be sure you take them to your veterinarian as soon as you can:

  • Staying in only one part of their tank.
  • Listless, sluggish behavior.
  • Abnormal swimming patterns, such as swimming on their sides.

Older fish are more prone to becoming sick or swimming on their sides due to their age and easily comprisable immune systems.

Fish that are stressed are also more likely to become sick, so, again, it’s best to make their aquariums as comfortable to live in as possible.

Food Issues

It is very important that you know what to feed your fish. Buying any random fish food off the shelf (without checking the ingredients first) may result in uneaten food sinking to the bottom of the tank.

Try to feed your fish foods that they might normally eat in the wild. This can be anything from live foods to certain aquatic plants to even the bacteria growing in your tank. It’s always best to start off with frozen foods and work your way from there.

If you really want to feed your fish healthy flakes or pellets, make sure you understand your fish’s eating patterns. Some fish will come up to the surface of the aquarium to look for their food, while others may prefer to dig around.

If your fish often swim up to the top for feedings, try feeding them fish flakes or other floating foods. If they like to dig around in the substrate, try giving them sinking pellets.

The food you give your fish could have something wrong with it as well. Check to see if their food has possibly reached its expiration date, smells off in any way, or if the food has been stored incorrectly.

What to do if your fish is not eating

What to Do If Your Fish is Not Eating

How to Encourage Your Fish to Eat

First things first, you should properly acclimate your fish. In short, this means you should ensure all your fish are safe and comfortable.

You might have to set up a separate quarantine tank for any ill, injured, pregnant, or particularly aggressive fish to protect your other species. This quarantine tank should be set up with a couple of familiar decorations, so they can feel comfortable acclimating to their temporary home. A few fake rocks or plastic plants taken from their original tank will suffice.

You should also remove your fish from their aquarium if you find any pressing issues with their water parameters (i.e. it contains too much of a certain chemical, the water’s too cold or too hot, etc.).

It’s also possible that your fish has just gotten bored of eating the same foods over and over. They may want something new. Try mixing their meals up with live foods instead of relying solely on pellets or flakes.

You could also change up the way you feed your fish. Instead of just sprinkling their food around the tank, you could instead feed them by hand. It may take some time before they warm up to the idea, though other fish might be too shy to try this at all.

When to See Your Vet

If your fish still does not want to eat after you tackle all the possible stressors you can think of, then it might be best to take them to your veterinarian to see what else could be wrong.

Why won’t my fish eat

Can You Overfeed Your Fish?

Overfeeding fish is actually quite easy to do. In fact, your fish might even encourage you to do it without you knowing!

Once you develop a feeding routine, they will come to expect food at certain times, or they may even try to get your attention by swimming up to the top of their tanks or right up to the glass to trick you into feeding them even more. No matter how much you might want to, however, just remind yourself that there are certain dangers to overfeeding fish.

Fish in the wild are will often eat whenever they feel hungry and food is available to them. Oftentimes, food sources can be scarce and they can go for days without eating, hence their opportunistic feeding behavior.

Fish raised in aquariums are no different. If you give them more food than normal, they may attempt to eat it all up even when they aren’t actually hungry. This can also lead to becoming fuller faster and leaving the leftover food to simply float there and rot.

If you see uneaten food lying around the tank, this isn’t a good sign. Your fish should always want to eat. Uneaten food degrades the water quality and upset the pH and chemical balances in the tank.

How Often Should Fish Be Fed?

How often you need to feed your fish generally depends on the species you keep in your aquarium. Most fish tend to thrive from only one feeding a day, though you can feed them twice a day, if you prefer. Try to keep the amount of food you give per feeding very small, so that none of it will go to waste.

You can typically feed your fish at any time of the day, unless they are nocturnal feeders, in which case you should feed them right before you head to bed at night.

There are a few exceptions to this limited feeding rule, however. For instance, herbivores have smaller stomachs that can’t hold much food, so these fish need to feed quite often throughout the day. It’s best to provide these fish with live plants to nibble on, so they won’t starve. As a bonus, this will keep them more active and interesting to watch.

Newly hatched fry and young fish who are not fully grown tend to eat much more as well. Try to frequently feed them special foods designed for fry at various times throughout the day.

Overfeeding fish

What Happens If You Overfeed Fish

Overfeeding fish often results in uneaten food being left to break down and rot, and rotten food left in the tank can lead to serious consequences, including lethal changes in the water chemistry. When left in the tank, the proteins found in most fish foods often break down into ammonia and nitrites, which are extremely toxic to fish. This can also stress them out and cause them to become sick.

Rotten food can also mess up the oxygen and pH levels in the aquarium. Breaking down food is an aerobic process, meaning that doing so uses up oxygen and produces carbon dioxide. With less oxygen in the tank for your fish to breathe, they will start to panic.

The water’s pH levels can also become more acidic during this aerobic breakdown process, leaving fish that prefer a higher pH level especially stressed out.

Of course, stress can cause your fish to become sick, and that will lead to its own problems.

Common Illnesses From Overfeeding

The most common illness fish can develop while stressed is fin rot, which is a condition where your fish’s fins develop a moth-eaten, shaggy appearance.

If allowed to eat more than they need to, your fish could also develop fatty liver, which is a disease that adversely affects your fish’s liver. If left untreated, your fish may even die from it.

Excessive Bacteria Growth

Uneaten food can also promote an explosive growth of bacteria if left in the tank. Your tank water will then slowly become hazy, cloudy, and generally unpleasant to look at.

While the bacteria themselves are often harmless, the haze still has the potential to upset your fish and stress them out. Bacteria reproduce every few hours or so, which means your tank can become a hazy mess overnight.


Fish can be quite the interesting pets to keep around, and it can be very worrisome when they stop eating all of a sudden. If you’ve tried your best to develop a comfortable aquarium for them and they still do not respond well, then take them to your veterinarian as soon as possible.

Have you ever experienced an appetite problem with your fish?

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