Can a Fish Have a Heart Attack? Let’s Examine the Facts!




Can Fish Have a Heart Attack

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Can a fish have a heart attack like a human? The answer to that question is yes. The heart is key to life because it circulates blood, gives oxygen to our body, and gets rid of waste. Heart attacks happen when an area of the heart doesn’t get enough blood.

Read on to find out how fish have heart attacks and how to prevent them.

How To Identify a Fish Heart Attack?

Heart attack symptoms in fish are hard to notice. Before a heart attack, your fish can act naturally and healthily. Even fish that aren’t showing signs of issues with heart health can meet a sudden death.

Heart Attack Causes in Fish

There are several factors that put fish at risk of a heart attack. Here are factors that affect the heart health of your fish.


A fish goes through stress just like a human and suffers from the effects of it similarly. When a fish is exposed to an environment it can’t handle, this increases the risk of cardiac death.

Fish can become stressed by improper water quality, overcrowding, aggressive tank mates, or illness. If your fish experiences stress regularly, this increases their risk of death. Stress leads to the failure of a fish’s internal organs and causes improper circulation, putting them at risk of heart disease.

Aggressive Tankmates

Choosing improper tank mates is a mistake that can cause stress in a variety of fish. Studying if your tankmate of choice will work well with your current fish is key.

Aggressive fish will bully other species of fish during eating or swimming and cause them undue stress which can negatively affect your particular species.

Improper Water Parameters

When water quality is poor, toxins begin to build up and decrease the immunity of your fish species, leading to the risk of illness and eventually congestive heart failure.

Uneaten food and ammonia wastes produced by fish eventually become toxins in your aquarium. These toxins can also build up if your filter fails, if you don’t change the water often enough, or if you are giving food in excess. When fish are exposed to these toxins, they become stressed, and their immune system leaves them open to disease.


Just like humans, fish can hear. They feel sounds through vibrations of sound waves and hydrostatic pressure. Sound waves are also felt differently depending on the type of fish and their size.

Loud sounds can distress fish of any size and lead to stress and a decline in health.

Large Water Change

Frequent small water changes for your aquarium are necessary, but large-scale water changes can cause issues.

When a sudden, large water change happens, the water chemistry changes so much that fish can’t handle it. Over time fish will become ill which can affect their blood pressure and lead to coronary heart disease.

Lack of Blood Supply

Just like humans, a fish’s organs operate because of blood flow. Blood gives the tissues oxygen and nutrients. When there isn’t enough oxygenated blood going to the organs it can lead to a heart attack.

Improper Tank Size

The walls of the aquarium predict their health. If your fish are being kept in an improper tank size this increases the likelihood that your fish will become stressed and sick.

Cardiac Arrest

Cardiac arrest and cardiovascular events that occur in the fish lead to restriction of the blood vessels and heart and lead to failure.

Water Hardness

The water hardness depends on the nutrients and contaminants in the aquarium water. If the water becomes too hard for the fish it can begin to affect a variety of fish and lead to skin diseases and increased toxins in the body.

Hard water also controls the fish’s blood supply and blood vessel function. Hard water leads to vein blockage that produces blood clotting and decreases blood flow to vital organs like the heart.


Fear in fish is not the same as it is in humans. Fish depend on the water and can easily become afraid with the addition of tankmates, new decor, or general changes to the aquarium. These changes affect their sense of security which negatively impacts their health.

Not Enough Water

If you don’t have enough water in your tank this can negatively affect your fish. As the water level lowers the oxygen and nutrient supply lowers. They also begin to have less space to move around, which can cause them to panic. This distress can then cause them to go into heart failure.

Lack of Blood Supply

Less oxygen means less blood supply. If there isn’t enough oxygen available in the aquarium, this can lead to fish death. Fish’s gills need enough blood to regulate breathing. If there is a disturbance in the available blood supply this will lead to fatality.

Heart Attack Prevention

The first measure to prevent a heart attack in your fish is maintaining proper water quality in your aquarium.

To improve the water quality in your aquarium, don’t overfeed your fish, test your water levels on a regular basis, and change the water at regular intervals. These factors will have significantly beneficial effects on the health of your fish.

To manage stress in your fish and prevent heart attacks follow these tips:

  • Change the aquarium water often to remove harmful substances that can negatively affect fish.
  • Check the water temperature, PH, hardness, ammonia, nitrite, and nitrate levels often.
  • Provide a quality filter for your aquarium
  • Avoid keeping your fish in an aquarium that is too small for them.
  • Don’t overcrowd your tank
  • Choose your tankmates wisely
  • Separate fish that become aggressive into a separate tank.
  • Feed your fish a high-quality, balanced, healthy diet, and feed them the proper amounts
  • Avoid loud sounds that can cause your fish to stress
  • Don’t do large water changes that can drastically change water chemistry. For more information about this, watch this video.
  • Treat underlying illnesses quickly
  • Keep the water level in your tank at an appropriate level

What Is a Fish Stroke?

Fish have brains so they do have the ability to have a stroke, however, there haven’t been any reported cases of this happening.

Just like in humans, a stroke occurs in a fish when the blood supply to a specific part of the brain is reduced and stops the brain from getting the nutrients and oxygenated blood that it needs to be able to function properly.

This decrease in blood flow can be caused by tumors, injury, blood clots, and more.

If a fish were to have a stroke, it would show symptoms such as…

Unfortunately, if your fish does have a stroke, there is no way to treat it and it can’t be helped.

Can a Koi Fish Have a Stroke?

Just like other fish, koi fish can also have strokes. They occur the same way as they do with other fish.

What Are the Signs of Illness in Fish?

When fish are ill just like humans, they tend to show symptoms in two ways, physical and behavioral.

Physical signs of illness include:

Behavioral signs of an illness can be more difficult to identify. If you don’t know your fish’s personality or keep track of its regular behaviors, it can be hard to identify changes.

Behavioral signs of illness include:

  • Incorrect body position
  • Negative or positive buoyancy
  • Avoiding specific tank areas
  • Increased hiding or decrease in social behavior
  • Different swimming behavior
  • Appetite changes or changes in feeding behavior
  • Scraping themselves against objects
  • Clamped fins
  • Schooling fish separating from the group

How Do I Know If My Fish Is in Pain?

Fish show that they are in pain in a few ways that are similar to humans and some that aren’t. The following are indications your fish is in pain.

  • Rapid swimming
  • Lethargy
  • Lack of appetite
  • Color change
  • Rapid gill movements
  • Hiding for extended periods of time
  • Less likely to show defensive behaviors
  • Slow during feeding, not eating or spitting food out


Just like a human, a fish can have a heart attack and can experience pain. The easiest way to prevent a heart attack and subsequent death of your fish is to keep its environment stable.

The proper tank size and water conditions are key factors when it comes to providing health benefits for fish. Regular water changes and avoiding overfeeding will also keep your fish in tip-top shape.

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