Koi Fish Swimming Upside Down: 4 Main Causes and Treatments

The surreal sight of your koi fish swimming upside down can be a nightmare. What does this unnatural koi (Cyprinus carpio) fish swimming behavior mean, and what should you do about it?

Koi fish swimming upside down can be due to swim bladder defects, poor water parameters, stress, or lack of food. Solutions to this problem include treating the fish for swim bladder infection, conducting regular water changes, and ensuring the fish has sufficient sinking food.

Keep reading as we dive deeper into the reasons why your koi fish is swimming upside down. We also provide solutions to this unnatural behavior so you can restore your koi fish’s normal swimming pattern.

1. Swim Bladder Defects

koi fish swimming upside down
Koi fish

The swim bladder is a crucial body part that determines how a fish swims. The organ enhances the fish’s buoyancy by regulating the amount of stored gas.

The swim bladder can encounter various defects if you don’t provide adequate care for your koi fish in terms of food and aquarium environment. Swim bladder defects can make koi fish to swim upside down due to poor buoyancy.

The swim bladder ensures that your koi fish swims normally through the following processes:

  • Inflation: The swim bladder inflates when the fish wants to increase buoyancy. This is achieved by introducing gases into the bladder to expand it and displace more water. As a result, the fish floats upwards.
  • Deflation: The swim bladder deflates when the fish wants to decrease buoyancy. This is achieved by releasing gases from the bladder to reduce the size, making the fish sink deeper into the water.

If the swim bladder becomes damaged or infected due to a poor diet or improper aquarium conditions, it impairs the above processes. The consequence is your koi fish swimming upside down.

Causes of Swim Bladder Defects in Koi Fish

A defective swim bladder in your koi fish can result from the following conditions:

Bacterial Infection

Bacteria are a common cause of swim bladder infection in fish. These bacteria result from poor water quality or overcrowded fish tanks. They can also be introduced into the tank via contaminated food.

Hydrophila/caviae and S. xiamenensis are the leading causes of bacterial infection in koi fish. The swim bladder in the koi fish has a pneumatic duct connected to the foregut. Due to this anatomic structure, it’s easier for bacteria to infect the swim bladder by ascending through the duct.

High nitrate level in the aquarium is the leading cause of these bacteria in aquariums. Nitrate is produced when bacteria break down the organic waste in the aquarium. If left unchecked, nitrates can cause swim bladder infections and affect your koi fish’s swimming behavior.


Constipation is another cause of swim bladder defects in koi fish. A constipated koi fish will have difficulty expelling gas out of its swim bladder to maintain the right amount of buoyancy. As a result, the fish will swim upside down and may eventually die if left untreated.

Constipation in koi fish is mainly caused by an improper diet with insufficient fiber or too much protein. Other causes of constipation in koi fish include the following:

  • Lack of exercise
  • Bacterial infection
  • Feeding excessive freeze-dried foods

Infection or Inflammation of the Digestive Tract

If your koi fish is swimming upside down, it may have inflammation or infection in its digestive tract. This can lead to swim bladder defects due to impeded digestion and absorption of nutrients. 

Some common causes of digestive tract infections include the following:

  • Protozoa and bacteria such as Vibrio, Aeromonas and Yersinia enterocolitica
  • Wrong feeding techniques that lead to the digestion of food in the wrong part of the digestive tract
  • Viruses such as birnavirus kanami-koi disease (FKD) and koi herpesvirus (KHV). These viruses are highly contagious and can cause various symptoms, including swim bladder defects in the common carp.

Treatment for Swim Bladder Defects in Koi Fish

The best way to treat a swim bladder defect in your koi fish is by pinpointing its exact cause. This will enable you to provide appropriate treatment that addresses the root cause appropriately.

If your koi fish is swimming upside down due to bacterial infection, you can treat it by:

  • Ensuring that the water quality in your aquarium is at the optimal level for koi fish. This includes maintaining a regular water change schedule and cleaning filters regularly.
  • Using an effective antibiotic such as kanamycin or oxytetracycline to treat the infection. Consult your veterinarian for more information on appropriate dosages and treatment duration.
  • Adding a probiotic supplement such as Bacto-Solve or ProbiotoX to promote beneficial gut bacteria in your koi fish. This will help restore balance to the digestive tract, reducing inflammation and the potential for infection.

For constipation-related defects in your koi fish, you should:

  • Incorporate a fiber-rich diet: When feeding your koi fish, ensure to incorporate fiber-rich foods like vegetables. Your fish needs dietary fiber to soften and increase the weight of the stool, making it easier to pass and prevent constipation. While doing this, you can limit protein foods to once or twice a week.
  • Increase the amount of physical exercise your koi fish gets. Exercising your koi fish enhances its muscles, making swim bladder inflation and deflation easier. You can exercise the fish by increasing the frequency and duration of its swim sessions.

Ultimately, you should strive to prevent bacterial infection in your koi fish by performing regular water changes and cleaning the tank regularly. This will remove any lingering bacteria from the aquarium environment and maintain good water quality for your koi fish.

2. Poor Water Parameters

Koi fish are temperate fish that need a specific water temperature and PH level to thrive in their aquarium environment. If these parameters aren’t optimal, your koi fish is likely to encounter swim bladder defects that make it difficult to swim and digest properly.

Moreover, poor water quality in the aquarium reduces the amount of oxygen needed to sustain the fish. Koi fish needs at least 6 ppm of oxygen for a quality life.

Low oxygen levels in your koi fish’s aquarium will force it to swim to the surface in search of oxygen. While on the surface, the fish doesn’t swim naturally through the gills. Instead, it swallows air through the mouth, a situation that inflates its stomach, leading to upside-down swimming and drowning.

High ammonia levels and nitrates in the tank are the leading causes of poor water quality.

Other contributing causes of poor water quality include the following:

  • Use of aggressive chemicals and detergents in your aquarium cleaning process
  • Overfeeding that leads to excessive nutrient pollution
  • Lack of regular water changes, resulting in excess waste buildup over time

The table below shows the optimum water parameters required for koi fish:

pH6.3 to 7.1
CO2 (mg/L)2.9 to 6.4
DO (mg/L)4.2 to 6.5
Temperature (°C)19.0 to 28.0
NO2 (mg/L)0.065 to 0.1439
NO3 (mg/L)0.0547 to 0.1164
NH3 (mg/L)0.0913 to 0.1739
Hardness (mg CaCO3/L)54.15 to 155.0
Optimum water parameters for koi fish

The signs to look for if you want to know if your koi fish tank has poor water quality include the following:

  • Excessive tan worms in the aquarium
  • White cloudy water
  • Red-looking water
  • Your koi fish breathing heavily or gasping after a water change
  • Ammonia spikes

Remedies for Poor Water Quality in the Fish Tank

If you notice your koi fish swimming upside down or showing other symptoms of poor water quality, take immediate steps to address the root cause. Some steps to take include:

  • Perform a water change: You should perform regular water changes in the aquarium. Water change ensures a balanced aquarium by diluting waste products like ammonia and nitrates. It’s advisable to do a 10 percent water change weekly if you have a small fish tank. Otherwise, you can do a 20 percent weekly water change for large fish tanks that exceed 150 gallons.
  • Clean the tank: Regular tank cleaning prevents bacteria and other organisms that reduce oxygen levels in the tank. When cleaning your koi fish tank, avoid using aggressive detergents or chemicals like bleach that can harm the fish’s delicate skin. Instead, you can use warm water to clean away the grime buildup on the walls of the aquarium.
  • Ensure optimum tank temperature: You should monitor and maintain the tank temperature for optimal water quality. Koi fish prefer a range of 19 to 28°C (66.2 – 82.4°F). You can maintain this temperature range by installing a thermometer in the aquarium to help you monitor and adjust the heater if needed.
  • Perform regular water tests: Testing your koi fish’s tank will help you identify any water quality issues before they become severe. Apart from temperature tests, you can use an electronic pH meter for pH tests. After that, you can use these test results to determine whether you need to perform more frequent or larger water changes.
  • Reduce feeding: Another way to improve poor water quality in your koi fish tank is by reducing feeding. Excessive food leads to nutrient buildup that hurts the fish’s overall health. You should feed your koi fish only once a day and ensure that the food is completely eaten up before adding more.

3. Stress

Stress in plecos is a common factor that most aquarists with this fish struggle with. However, this doesn’t mean your koi fish is immune from stress.

A stressed koi fish may swim upside down due to insufficient energy it needs for swimming to swim.

Koi fish can experience stress for several reasons, including:

  • Inappropriate tank conditions, such as high ammonia levels, poor water quality, or low oxygen levels
  • Aggressive tankmates that bully the koi fish
  • Too much handling by you or other people in the household
  • Poor nutrition
  • Overcrowding in the tank
  • Excessive sunlight exposure in outdoor ponds
  • Presence of predators in the tank
  • Sickness or parasites

As a koi parent, knowing when the fish is stressed might be challenging. Luckily for you, here are some signs of a stressed koi fish:

  • Lethargy
  • Gasping of air at the surface
  • Loss of appetite
  • Frequent gill movements

Remedies for Stress in Koi Fish

If you notice the above signs of a stressed koi fish, you must take immediate action to restore normalcy.

Some tips to help you eradicate stress in your koi fish include:

  • Provide sufficient spacing: Ensure the tank has enough space to accommodate your koi fish. As a rule of thumb, you should have one adult koi for every 250 gallons of water.
  • Add stress-reducing plants and decorations: Plants can help reduce stress in your koi fish. You should add aquatic plants like the Java moss or java fern to provide a sense of security for the fish. Other decorations include rocks and driftwood, which also have a calming effect on the fish.
  • Implement regular water changes: Cleaning your koi fish tank regularly reduces the buildup of waste products that can lead to stress. Be sure to use fresh distilled water when performing a water change. Never use tap water for water changes as it contains chlorine.
  • Limit handling and other interactions: To prevent stressing out your koi fish, you should avoid touching it frequently. This will not only reduce stress in the fish but also improve its health and well-being.

4. Lack of Food

Your fish needs sufficient food to serve as the building blocks for all the processes within its body.

Like any other living organism, your koi fish needs nutrients to survive and get energy for movement.

Koi fish uses their fins to propel themselves forward, and energy is required for this. However, if the fish doesn’t get enough nutrients or have a poor diet, it will not get enough energy to swim correctly.

You might notice the following signs if your fish is getting insufficient food or is being fed with the wrong type of food:

  • Swimming upside down
  • Resting on the bottom of the tank or pond
  • Skinny, pale body
  • Loss of appetite and weight loss

Treatments for Poor Nutrition in Koi Fish

If you notice any of these symptoms in your koi fish’s diet, you need to take action immediately to improve its nutrition. Some tips for improving poor nutrition include:

  • Feeding your fish with a balanced diet: A balanced diet will ensure that the fish receives all the nutrients it requires for proper functioning.
  • Ensuring that your koi fish gets enough food: Be sure to feed your fish a sufficient amount of food it can completely consume within 3 to 5 minutes.
  • Providing supplemental foods: You should add foods such as live or frozen bloodworms and brine shrimp since they are rich in nutrients and essential fatty acids.
  • Add nutritional supplements: Apart from regular food, ensure your koi gets supplements like vitamins, amino acids, and minerals to promote good health.

A crucial consideration is ensuring all the foods sink to the bottom of the tank or pond. Floating fish foods can get stuck in the filter or pump, causing them to malfunction.

Frequently Asked Questions

How Do You Fix a Koi Swim Bladder?

You can fix a Koi fish swim bladder by providing Epsom salt, withholding food for a few days, and offering blanched peas. If you want to use Epsom salt, dissolve the salt (without additives or fragrances) in a separate container of water, then slowly add the water to the quarantine tank containing the pleco. Ensure to follow the recommended dosage instructions based on the volume of water.

Fasting is the best way to fix koi swim bladder if you suspect the issue is caused by overfeeding or constipation. If this is the case, stop feeding the fish for three days and observe if that solves the problem.

How Do You Save a Koi Fish That Is Upside Down?

You can save a Koi fish that is upside down by solving the swim bladder problem. The best way to do that is by fasting the koi fish and then feeding the fish cooked or frozen peas to unblock the swim bladder.

Why Is My Koi Floating Upside Down But Still Alive?

If your koi fish is floating upside down but still alive, it’s going through a positive buoyancy disorder due to excessive internal gas. This problem emanates from an over-inflated swim bladder. The solution is to put the fish in a warm water bath containing 3 grams of Epsom salt per liter of water for about 30 minutes. You can repeat this procedure until the problem gets solved.

Final Thoughts

Your koi fish swimming upside down is a sign of a serious issue you must address urgently. If you notice any of the symptoms above, take appropriate measures to improve your fish’s nutrition and environment.

It’s advisable to consult an aquatic veterinarian if you try different approaches without success.

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