angelfish gasping for air

Why Is My Angelfish Breathing Fast?

Angelfish are graceful creatures that appear calm and poised, so it’s obvious when they start gasping for air. Breathing fast is a bad sign, as angelfish only pant or gasp when they’re struggling to breathe.

Angelfish breathe fast due to a lack of dissolved oxygen in the tank. When stressed or sick, their immune systems and gills function suboptimally, making it harder to breathe, hence the gasping. The fish will start suffocating if the tank’s pH level, nitrates, or temperature are incorrect.

When you notice these signs, you’ll need to aerate the water manually and replace around 15% of the unclean water. Also, you can get air stones or other devices that add air to a tank. If your fish are overcrowded, you’ll need to separate the bigger ones from the smaller ones.

How Fast Should Fish Breathe?

The breathing pattern of healthy angelfish is barely noticeable. At a glance, you shouldn’t be able to tell when it is and isn’t breathing. Upon closer inspection, the inhales and exhales should be subtle.

Young angelfish breathe faster than adult angelfish because they can’t take in as much oxygen due to their size. However, young angelfish should behave normally, despite the rapid breathing.

Bad kinds of angelfish breathing include the following:

  • Breathing hard
  • Gasping for air
  • Opening and closing its mouth rapidly
  • Gasping at the surface of the tank
  • Breathing only at the surface

What It Means When Angelfish Breathe Heavily

Heavy breathing, along with the signs above, is a strong indication that your fish are suffocating. While angelfish can breathe water, they still need oxygenated water.

If there isn’t enough oxygen in the tank, or their body cannot process it, they’ll grow ill. As the oxygen deprivation continues, the fish may die.

Besides oxygen levels, angelfish breathe quickly when:

  • Long-term stressed
  • Sick
  • Chased
  • In shock
  • Living in improper water conditions

Reasons Why Angelfish Suffocate

Angelfish may only provide subtle indicators that they’re sick or struggling. You’ll need to rely on these signs and clearer indicators from their living environment.

Lack of Oxygen in The Tank

You may think your fish couldn’t possibly suffocate. After all, fish don’t breathe air; they breathe water, which is hydrogen and oxygen.

What fish breathe isn’t pure oxygen but rather dissolved oxygen. In nature, oxygen from the atmosphere gets dissolved in water by pouring over rocks. Cold water has more oxygen than warm water, so rapidly moving bodies of water contain more oxygen than still bodies.

As such, if your aquarium’s water doesn’t have any movement to ‘fill’ it with oxygen, it’s deadly to the angelfish. They will start to suffocate. You also can’t rely on the fish’s ability to take oxygen from the surface of its tank. This will keep it alive for a while, but it will still grow ill.

That’s because fish need water to survive. Fish breathe by taking in water through their mouths, and that water passes through their gills (which are full of blood vessels). The dissolved oxygen in the water makes it to the fish’s red blood cells through the blood vessels.

Fish don’t have the bodily functions to take in pure oxygen and have it travel to the bloodstream like humans. This is why, if you take a fish out of the water, it won’t be able to breathe. The only way for it to acquire oxygen is if it’s transported by liquid through its blood vessels. Here’s how to tell if an angelfish lacks oxygen in the tank:

Slow Swimming

When taking in oxygen, an angelfish’s cells perform aerobic breathing. This is when oxygen molecules are converted into cellular energy. When angelfish don’t have enough oxygen to convert into energy, they become lethargic. They will swim very slowly as if they’re tired.

Gulp For Air At The Surface

There is more dissolved oxygen at the water’s surface than below, which may keep the fish alive for some time. Eventually, they run out of oxygen and die.

What if your angelfish is at the bottom of the tank? It means the fish doesn’t have enough energy to swim to the surface and is close to death. The oxygen levels are lowest at the bottom of the tank due to all the waste. This is the last place an angelfish would want to be if it was suffocating.


Angelfish change colors often, for positive and negative reasons. When suffocating, an angelfish’s color will slowly fade away.

Angelfish change and maintain their color through a cellular process that requires energy. The color of a suffocating angelfish fades because the body no longer has the energy to maintain its color.

Opening And Closing Mouth

The first step for fish breathing is taking in water through the mouth. If an angelfish is opening and closing its mouth repeatedly, it’s struggling to breathe.

Lack Of Appetite

A fish that is slowly suffocating won’t be interested in food. The body will also try to reserve as much energy as possible to keep the angelfish alive. Anything that requires extra energy, such as eating and digesting food, will be low on their list.

angelfish breathing at surface

Swimming Near The Filter

Some aquarium filters release a lot of bubbles, which contain oxygen. If your angelfish swim near the filter, it means it’s the only place in the tank where they can get oxygen.

Water Tests

Testing the oxygen levels is ultimately the best way to know if your fish lack oxygen. There are 2 ways to test the oxygen levels:

  • A chemical test kit
  • A portable dissolved oxygen meter.

A portable dissolved oxygen meter costs more than a chemical test kit, but the results are more accurate.

SurvivabilityDissolved Oxygen Levels (milligrams per liter)
No chance of survival0-4.0 mg/L
Very few fish can survive4.0-6.5 mg/L
Some big fish might survive, but small fish won’t6.5-9.5 mg/L
All fish can survive9.5-12mg/L

Long-Term Stress

Stress is beneficial to angelfish because it gives them the adrenaline needed to escape dangerous situations. However, long-term stress due to constant exposure to threats can compromise angelfish’s immune system, interfering with their ability to breathe. The signs of stress in an angelfish are:

Lack Of Appetite

If the angelfish fears that it’s in danger, it won’t eat so that it can focus on avoiding the threat. As it feels stressed and is low on energy due to a lack of food, it may gasp.

Avoidant Behavior

This usually happens when a tank is overcrowded. If there are too many fish, the angelfish will try:

  • Swimming to a secluded area of the tank
  • Hiding behind plants

This also happens when other angelfish are in the middle of trying to acquire mates. They will establish dominance over the other fish or fight to claim territory.

If one angelfish doesn’t feel up to the possible fights, it will get stressed while protecting itself. This added danger makes it difficult for the fish’s body to breathe easily.

Aggressive Behavior

Stress can make angelfish lash out. When they feel cornered, some angelfish will attack other fish since they feel they have no other place to go.

In their natural habitat, angelfish will try to swim as far away from danger as they can. In small aquariums, that option isn’t available as the stress will affect their ability to process air.

Lethargic Swimming

Sudden movements from a human outside the tank or a tankmate can stress angelfish. It will feel in danger and begin swimming quickly to avoid the threat. Not only is this exhausting, making the fish breathe harder, but it compromises the health of its body.

In tandem, the fish will quickly get tired out. Slow swimming is a sign of long-term stress.

Rapid Changes In Color

Angelfish change color depending on the illumination of their environment. If the lights are low, their color will fade, and if the lights are bright, the scales will also get brighter.

Light levels change faster in a house than in an angelfish’s natural environment. A room can become brighter with the flick of a light switch, and this rapid change in the environment can stress angelfish.

Pale Stripes

When hiding from a predator, angelfish will often hide behind plants and fade the color of their stripes. If the stripes are faded for more than a few days, the angelfish has long-term stress. You’ll notice the fish gasping or ‘panting’ as a result.

Improper Water Conditions

Apart from oxygen, angelfish will become stressed from lacking:

  • pH levels
  • Nitrate levels
  • Nitrite levels
  • Ammonia levels

If it goes on for long enough, the fish will eventually suffocate. Certain chemicals can also harm the angelfish’s gills, making it harder for them to breathe. Make sure to check the gills for any sign of redness or discoloration.

Regularly test the water and make sure everything is balanced. Sometimes, angelfish don’t show the symptoms of stress quickly enough for you to do something about it.

Injury And Illness

Any illness or injury is taxing on an angelfish’s body. Certain illnesses compromise the function of the gills, making it hard for angelfish to breathe. Here are some signs that your angelfish is ill or injured:


If your angelfish’s stomach looks rounder than usual, it is most likely bloated. This can be because of overfeeding, bacteria, constipation, pregnancy, or tumors.

Raised Scales

Certain diseases can cause the scales on a fish to lift and protrude from the body. These diseases usually affect the gills to a heavy degree.

Torn Fins And Cuts

Depending on how badly the angelfish is injured, physical wounds take a lot of time and energy to heal. As the body prioritizes healing, an angelfish’s breathing can become labored. However, this mostly happens with angelfish that are gravely injured.

Being Chased By Tank Mates

Fish are opportunistic. Even when there is plenty to eat, they can still turn cannibalistic. When a fish in the tank is slowly dying due to injury or disease, the other fish will react.

This is often with nibbling and chasing. The stress of running from other fish, and the act of fleeing in general, may cause the fish to breathe heavily.


Just like humans turn a different color when they are physically ill, angelfish will change the color of their scales when sick.

It depends on how healthy the angelfish was before getting injured or sick. Usually, the discoloration begins with the angelfish’s original color dulling. When the angelfish is near death, the color gets paler. This will be accompanied by heavy breathing.

Why Is My Angelfish Breathing Fast After a Water Change?

Changing the water in a tank can be complicated, especially for first-time aquarium owners. Still, it’s necessary to change the water every 2 to 4 weeks to ensure the environment is clean.

When doing so, consider each element carefully. If you miss one aspect of the water change, you can make your fish struggle to breathe. Here are points you may have missed:


When keeping angelfish, the temperature of an aquarium must remain between 78 and 83 degrees Fahrenheit. If the newly added water is warmer or colder than the current water, it could shock their system and cause them to breathe faster.

Always check the water temperature, and match that temperature to the new water.


Test the amount of salt in the water. Aquarium salt can be used to treat the water for diseases. However, the more salt there is, the less dissolved oxygen is in the water.

Most pet angelfish are freshwater or don’t need a lot of salt in their water. However, adding a bit of aquarium salt helps rid the tank of germs. The amount depends on the tank size and the number of fish in the tank.


While changing the water and cleaning the tank, the fish may have breathed in debris, such as gravel or sand. Besides frequently changing the water, the bottom of the tank should be cleaned, and the gravel should be replaced occasionally.


Always make sure that the new water you add to the tank is:

  • Filtered
  • Matches the chemical levels of the water in the tank

The new water should also neutralize any pathogens, metals, and bacteria.

Water Change Schedule

When you change the water, it’s important to have a strict schedule. Your angelfish may get too accustomed to the water they swim in. Then, no matter how badly it needs to be cleaned, the old water is essential to their survival as new water might send them into shock.

To avoid this problem, be sure to change the water regularly. Don’t let it get too dirty. It’s also important not to change the water too frequently, as this greatly stresses them. By setting a fixed schedule, you can be sure to avoid issues.

do angelfish need air bubbles?

How To Increase Dissolved Oxygen in an Aquarium Without a Pump

So, your fish aren’t getting enough oxygen. How do you fix it? Traditionally, people use water pumps to aerate the water in their fish tanks. This creates a flowing current, which helps dissolve oxygen in the water. However, sometimes a water pump isn’t readily available. It may also fail to solve your problem fast enough.

If a pump is out of the question, you have other options. Here are emergency solutions, as well as long-term solutions.

Quick Solutions

If your angelfish are suffering, it’s best to act fast. Take these steps to get them out of immediate danger.

Increase airflow

If the aquarium has a lid, open it and allow the water to be exposed to air.

Aerate The Water

This can be done by increasing the water movement as still water doesn’t move fast enough to dissolve oxygen. You can temporarily help by making waves in the water and moving it around.

  • Take a clean glass container
  • Begin taking water from the tank
  • Pour it back in from up high

The splashes will create enough movement to begin trapping oxygen in the water. The movement will help dissolve said oxygen and give your angelfish what they need.

Change The Water

For a slightly more long-term fix, change the water. You should replace 15% of it with fresh water that (most likely) has more oxygen than the present water. This will:

  • Fix the issue for now
  • Help stir the original water and give it more oxygen

You should be careful with this method, however. The change might upset the fish more if:

  • You recently changed the water
  • The fish are under too much stress from an already inadequate environment

Remove Waste

Dissolved oxygen levels are low at the bottom of the tank. That because it’s where you’ll find the most:

  • Bacteria
  • Spoiled food
  • Waste
  • Algae

All these materials use up oxygen. By removing the waste, you can increase the overall dissolved oxygen levels of the tank.

Long-Term Solutions

If the aquarium isn’t completely fixed, your fish will eventually suffer again. To make sure your fish have a good environment to thrive in, apply these changes:

Make Sure To Change The Oxygen Levels Adequately

The bigger the fish, the more oxygen they take up. This is why smaller fish breathe faster than bigger fish, as they take in smaller amounts of oxygen due to their size.

If you have a tank full of juvenile angelfish, you should increase the dissolved oxygen levels as they grow. Your angelfish may be fine with the dissolved oxygen levels while they are small. However, that will change in the future.

Air Stone

Air stones are small machines that you place at the bottom or side of the tank. They release a stream of continuous bubbles that helps dissolve oxygen and create small waves. They are:

  • Inexpensive
  • Easy to install
  • Especially perfect for aquarium owners with smaller tanks

Add Aquarium Plants

Aquarium plants take in carbon dioxide and release oxygen. Angelfish in particular like:

  • Water wisteria
  • Java ferns
  • Water sprites
  • Java moss

The downside is that the plants need to be looked after. Otherwise, they will decay. If this happens, the plants will become nothing but waste at the bottom of the tank, taking up oxygen.

Add A Waterfall Filter

Adding a filter, especially a waterfall filter, will create waves and aerate the water. Make sure the filter isn’t too strong and creates a fast current.

Angelfish are native to the slow-moving rivers of South America and aren’t accustomed to swimming in fast currents. If the filter creates a tank environment where the fish need to swim faster, they’ll have trouble breathing.

Change The Type And Number Of Fish in The Tank

You might need to look into the type of fish that live with your angelfish. That’s especially true if you own species of differing sizes.

Bigger fish will always take up a lot of oxygen. You might have to separate your angelfish from the bigger ones by putting them in separate tanks or rehoming them.

Energetic fish that swim quickly around the tank will also take in more oxygen. The rapid movement might startle your angelfish and stress them out, leading to breathing problems.

Angelfish should never breathe fast. If they do, check their environment, tankmates, and health.