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Home > Goldfish > Why Is My Goldfish Swimming Upside Down? 6 Vet-Approved Reasons

Why Is My Goldfish Swimming Upside Down? 6 Vet-Approved Reasons

sick goldfish swims upside down in aquarium

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Dr. Lauren Demos

Veterinarian, DVM

The information is current and up-to-date in accordance with the latest veterinarian research.

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Goldfish are one of the most popular freshwater fish available. Many different varieties of goldfish are kept as pets, from common to fancy goldfish. Goldfish are generally hardy and healthy fish that are quite active in an aquarium. So, when they start swimming abnormally or even upside down, it is a cause for concern.

Let’s take a look below at the six common reasons your goldfish has started swimming upside down.

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The 6 Reasons Why Your  Goldfish Is Swimming Upside Down

1. Swim Bladder Issues

The most common reason for goldfish to swim upside down is swim bladder issues. Goldfish have a swim bladder organ that they use to maintain buoyancy in the water.

Their swim bladder allows them to move in the water and when there is a problem with it, your goldfish will start to swim upside down or abnormally. They will have difficulty moving in the water and struggle to stop themselves from sinking or floating. It is also known as swim bladder disease or disorder, although it isn’t necessarily a disease itself.

Swim bladder issues are often seen in fancy goldfish since they have compressed bodies and limited space in their coelomic cavities. If you overfeed fancy goldfish, their enlarged stomachs can put even more pressure on their swim bladder which may result in buoyancy issues. Usually, goldfish experience swim bladder issues when the water quality is poor (such as high ammonia and nitrites). However, infections or injuries to their swim bladder can also cause problems. Some goldfish are predisposed to swim bladder issues from birth.

Certain extreme fancy goldfish body modification has impacted their swim bladder from birth, so they might struggle with buoyancy issues throughout their life.

2. Ammonia Poisoning

Signs your goldfish has ammonia poisoning:

  • Lethargy
  • Black burns on fins and scales
  • Labored breathing
  • Lack of appetite
  • Difficulty swimming

Goldfish are continuously producing waste in their water, and alongside their food, this causes waste to build up in the water. Ammonia is the waste product from their poop, urea, and food. In a well-established aquarium with good biological filtration, ammonia will be processed into nitrites and finally nitrates, the less toxic form.

Goldfish generally have a high bioload and produce a lot of waste. This is one of the reasons they need good filtration and spacious fish tanks. In a new, overcrowded, uncycled, or poorly maintained aquarium, ammonia can become a serious problem for goldfish.

The safest level of ammonia for goldfish is 0 ppm. Slight traces of ammonia are detected by a liquid testing kit and can be dangerous for goldfish. They can start to show signs of ammonia poisoning, which is often fatal without immediate treatment. In severe cases, the ammonia in the water can burn your goldfish from both the inside and outside. This is incredibly damaging to their internal organs and gills, causing your goldfish to appear listless and struggle with buoyancy in the water.

In severe cases, the ammonia burns on their fins and scales can affect their ability to swim upright.

goldfish floating upside down
Image Credit: Lim Tiaw Leong, Shutterstock

3. Nitrite Poisoning

Signs your goldfish has nitrate poisoning:

  • Rapid breathing
  • No appetite
  • Lethargy
  • Browning gills
  • Difficulty swimming
  • Laying upside down at the bottom of the aquarium
  • Red streaks in fins

Just like ammonia, nitrite is equally as toxic to goldfish. The nitrite levels usually rise during an ammonia spike. High levels of nitrite in the water may cause methemoglobinemia in goldfish, which affects the way the protein (hemoglobin) in a goldfish’s red blood cells carry oxygen to their tissue.

This is often fatal to goldfish and can alter the way they swim and breathe. If a goldfish is suffering from nitrite poisoning, you will notice that they have difficulty swimming upright or normally, and their gills may develop a brownish coloration.

The safest level of nitrite for goldfish is 0 ppm, and signs of toxicity usually occur in concentrations as low as 0.75 ppm.

4. Nitrate Poisoning

Signs your goldfish has nitrate poisoning:

  • Disorientation
  • Erratic swimming
  • Lethargy
  • No appetite
  • Difficulty swimming
  • C-shaped body

Although nitrate is the less toxic byproduct from the nitrogen cycle, it is still harmful to goldfish at high levels. Goldfish generally tolerate around 20 ppm of nitrate in the water before showing signs of toxicity. Most of the water nitrates are diluted during water changes or used by live aquarium plants. However, nitrates can still negatively affect goldfish in several ways.

A goldfish who is suffering from nitrate poisoning will experience disorientation and difficulty swimming. Their bodies usually form an upside-down “C” shape, which is a distinctive sign of high nitrates in the water.

sick goldfish swimming upside down in aquarium
Image Credit: M-Production, Shutterstock

5. Low Oxygen

Oxygen is incredibly important for goldfish, even in an aquatic environment. They rely on oxygen for basic survival. When the oxygen is low in the aquarium, or your goldfish has a disease that affects their gills, they will struggle to get enough oxygen. Very warm water in a goldfish tank generally holds less dissolved oxygen, which can cause your goldfish to start gasping at the surface of the water. Also, any infections that affect goldfish gills will affect how they breathe underwater.

In severe cases where a goldfish isn’t receiving enough oxygen, their swimming behavior will be compromised. Your goldfish might appear listless at the bottom of their aquarium, or they will float upside down near the surface. If the water quality is good, then low oxygen levels might be a problem. This is especially true if the water is warmer than usual and there is no aeration system.

6. Fin Rot or Injuries

Fish use their fins to swim and stabilize themselves in the water. If their fins have been damaged from a disease or injury, they will have difficulty maintaining an upright swimming position. This can cause them to swim upside down, sideways, or struggle to swim at all. Once your goldfish has been treated for any diseases or injuries that affect their fins, it can take a while for the fins to regrow. The regrowth will look semi-transparent and slightly whiter than their usual fins.

sick goldfish swimming upside down
Image Credit: M-Production, Shutterstock

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How Can You Help an Upside-Down Goldfish?  

The first step to correcting your goldfish’s upside-down swimming behavior is to determine the main cause. Have you recently overfed your fancy goldfish or skipped a water change? Is the water quality poor from overfeeding or overcrowding? These are important questions to consider if your goldfish has started swimming upside down.

Test The Water 

The water parameters (ammonia, nitrite, and nitrate levels) are not visible in an aquarium. You will need to use a liquid water testing kit to get an accurate reading. The test will help you determine what parameters are an issue in the water. Allowing their aquarium to undergo the nitrogen cycle ensures that there is an establishment of beneficial bacteria to convert their waste properly.

If any of the levels are above the ideal amount, doing water changes can help dilute it. You can also use ammonia-neutralizing products that are formulated for freshwater aquariums. 

close up of hands adding drops to test PH or nitrite of freshwater aquarium
Image Credit: Ladanifer, Shutterstock

Consider Their Feeding Habits 

Overfeeding your goldfish is not recommended, especially for fancy goldfish who already have compressed bodies. You might find that your fancy goldfish become “floaty” after a large meal, which indicates that they might be eating too much at once. You should ideally feed fancy goldfish small meals once or twice a day, and as much as they can eat within 3 to 5 minutes.

Lower the Water Temperature

Goldfish are temperate water fish that can handle both slightly warm and cold water. However, water that is too warm can affect their oxygen intake and cause a range of problems. Gradually lowering the water temperature and aerating the water can increase the amount of dissolved oxygen.

Add an Aeration System

Surface agitation, whether it’s from a filter’s spray bar or a bubbler, is going to help aerate the water. This ensures that there is enough gaseous exchange happening at the surface while increasing the dissolved oxygen in the water.

oxygen bubbles under water in the aquarium
Image Credit: Pavel Kruglov, Shutterstock

Do Frequent Partial Water Changes 

When your goldfish are experiencing problems from poor water quality, water changes are incredibly beneficial. You can do frequent partial water changes to your goldfish aquarium every day in situations where the ammonia, nitrite, or nitrate levels are high. In severe cases, a 30% to 50% water change might be necessary every 4 hours. Using a siphon can help suction out waste products that have accumulated in the substrate, which would contribute to water quality issues. 

Treat Your Goldfish for Diseases

Many diseases and infections that affect goldfish can influence their swimming patterns. After you have determined the type of disease your goldfish is experiencing you can begin treating them with medication. It is probably best to move the sick goldfish into a separate tank for treatment so that the medication does not spoil their original aquarium water. Their treatment tank should have an aeration system and clean water.

It can take a few days or weeks before your goldfish is fully healed before their swimming behaviors return to normal.

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As we discussed above, this abnormal behavior is typically caused by poor water quality, swim bladder problems, fin injuries, and even low oxygen levels. However, swim bladder issues are the most common reason for goldfish to swim upside down.

Usually, an upside-down goldfish can make a full recovery with proper treatment and necessary environmental changes. In some cases, goldfish with a compromised swim bladder may have difficulty swimming normally again. It is common for fancy goldfish to experience recurring buoyancy issues that make them swim upside down, typically after a meal or infection. If that is the case, you will need to regularly maintain their aquarium and monitor their feeding habits to prevent their swim bladder issues from returning.

Featured Image Credit: M-Production, Shutterstock

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