7 Reasons Your Fish Is Swimming Sideways (& What To Do)

Last Updated on 2025-11-10

Don’t panic—seeing your fish swim sideways or upside down is alarming, but your fish likely isn’t dying. What you’re witnessing is most likely swim bladder disease, a common condition that affects countless aquarium fish each year. The good news? Swim bladder issues respond exceptionally well to early intervention, especially when the cause is dietary or environmental—which accounts for the majority of cases.

QUICK ACTION CHECKLIST: What To Do Right Now

If your fish is swimming sideways, take these steps immediately:

• Test your aquarium water for ammonia, nitrite, and nitrate (if you have a test kit available)
• Check the water temperature with a thermometer
• Stop feeding your fish for the next 24-48 hours
• Prepare for a partial water change (25-30%) to improve water conditions
• Move the fish to a quiet, separate tank if possible, or reduce stress by dimming tank lights

These actions address the most common causes and buy you time to identify the specific problem.

The 7 Reasons Your Fish Is Swimming Sideways

1. Swim Bladder Disease (The Main Culprit)

The swim bladder is a gas-filled internal organ that functions like a balloon, allowing fish to control their depth and stay upright. When this organ malfunctions, fish can’t maintain buoyancy and end up swimming sideways, upside down, or floating helplessly at the surface.

Most Common Cause: Constipation and Bloating

Overfeeding is the #1 reason fish develop swim bladder problems. When fish consume too much food, their stomachs become so bloated that internal organs press against the swim bladder, preventing normal function. Dry flakes and freeze-dried foods make this worse because they expand significantly in the fish’s digestive system. Floating foods cause additional problems—when your fish gulps air while eating surface foods, that air enters their digestive tract and creates gas pressure on the swim bladder.

What To Do:

• Fast your fish for 3 days to allow complete digestion and relieve pressure
• Feed only what the fish can eat in 2-3 minutes
• Switch to sinking, high-quality pellets instead of floating flakes
• Pre-soak dry food in tank water for a few seconds before feeding to prevent expansion
• After the fasting period, offer blanched green peas (high in fiber) 2-3 times weekly to promote digestive health

Other Swim Bladder Causes: Bacterial infection (inflames the swim bladder), physical injury from fighting or collision, internal organ enlargement pressing on the bladder, or parasitic infection affecting digestion. If you suspect infection, consult an aquatic veterinarian about appropriate antibiotics.

2. Poor Water Quality (The Silent Killer)

High levels of ammonia, nitrite, or nitrate are toxic to fish and can cause neurological damage, leading to erratic and sideways swimming. Poor water quality also creates chronic stress that suppresses your fish’s immune system and can inflame the swim bladder and surrounding tissues.

What To Do:

• Perform an immediate 25-50% water change to dilute toxins
• Add a water detoxifier like Seachem Prime to neutralize ammonia and chlorine
• Test water daily until parameters stabilize (ammonia and nitrite must be 0 ppm)
• Establish a maintenance routine: 25-30% water changes weekly, filter maintenance every 2-3 weeks
• Check parameters regularly: Use quality test kits to monitor ammonia, nitrite, nitrate, and pH

The Filter Solution: Invest in a filter rated for 3-4 times your tank’s water volume per hour. This provides adequate filtration to prevent toxic buildup that triggers swim bladder problems and stress.

3. Overfeeding and Poor Diet

Overfeeding directly links to constipation and swim bladder problems. Many beginners don’t realize how little food fish actually need—overfeeding is one of the most common mistakes in aquarium keeping. Low-quality foods compound the problem because they contain fillers that don’t provide nutrition.

What To Do:

• Feed only what your fish can consume in 2-3 minutes
• Feed once or twice daily, never more
• Never leave uneaten food in the tank (remove after 5 minutes)
• Use high-quality, species-appropriate food (research your specific fish species)
• Avoid exclusively feeding floating pellets or flakes—use sinking options
• Pre-soak floating foods to help them sink
• Fast your fish one day per week to promote digestive health

4. Sudden Temperature or pH Shock

Fish are extremely sensitive to environmental changes. A sudden shift in water temperature or pH during a water change can shock their nervous system, causing temporary swim bladder dysfunction. Rapid changes stress fish, interfere with their metabolism, and can trigger constipation.

What To Do:

• Always match the temperature of replacement water to your tank water (use a thermometer)
• Make any pH adjustments slowly over several days—never attempt drastic pH changes
• Acclimate new fish gradually by floating them in the bag for 15-20 minutes before introducing them
• Maintain a stable water temperature between 72-78°F for most tropical species
• Use a reliable heater with a thermostat to prevent day-to-night temperature swings

5. Physical Injury or Trauma

Fish can suffer physical injuries to their swim bladders or bodies from fighting with aggressive tank mates or colliding with sharp aquarium decorations. Direct damage prevents the swim bladder from functioning properly.

What To Do:

• Move the injured fish to a quiet quarantine or hospital tank immediately
• Reduce stress by keeping the tank dimly lit and free of disturbances
• Maintain pristine water conditions to support healing
• Avoid handling the fish—unnecessary touching adds stress
• Review tank mate compatibility and remove aggressive fish if necessary
• Remove or smooth any sharp decorations that could cause injury

6. Bacterial or Parasitic Infections

Beyond just the swim bladder, serious bacterial or parasitic infections can weaken a fish to the point that it can no longer maintain buoyancy. Parasites like callamanus worms attach to the digestive system, creating blockages that pressure the swim bladder. Bacterial infections can directly inflame and infect the swim bladder itself.

What To Do:

• Look for other signs of infection: white spots (Ich), red streaks, torn fins, sores, extreme lethargy
• Consult an aquatic veterinarian for proper medication recommendations
• Use a quarantine tank for medication administration to avoid affecting the main tank
• Complete the full treatment course even if symptoms improve
• Do not attempt to self-treat with random medications; improper treatment can worsen the condition

7. Genetics or Old Age

Some fish species, particularly fancy goldfish and fancy bettas, are genetically predisposed to swim bladder issues. Additionally, as fish age, internal organs can begin to fail, affecting buoyancy control. These cases often cannot be cured but can be managed.

What To Do:

• Provide an enriched, stress-free environment with proper hiding spots
• Use a shallower tank to make reaching the surface easier
• Maintain perfect water quality to support overall health
• Feed a high-quality diet with adequate nutrition
• Focus on comfort care rather than cure—make the fish’s remaining life as peaceful as possible

Understanding Fish Twitching and Sideways Swimming

Sometimes fish twitch and swim sideways simultaneously, which may indicate shimmy—a condition where fish wave their bodies side-to-side rhythmically. This usually accompanies fin clamping, unusual head movements, rapid breathing, and general distress.

Shimmy indicates severe environmental stress or serious illness rather than purely digestive issues. Primary causes include water quality crashes, temperature extremes, nutritional deficiencies, or parasitic infections affecting the nervous system. Address the underlying environmental problem first: test water parameters, perform water changes, and eliminate stressors.

Why Is Fish Bloated and Swimming Sideways?

A bloated belly combined with sideways swimming usually points to digestive problems or infection. Here are the specific causes and solutions:

Overeating

When a fish eats too much, its stomach becomes bloated. To fix this, stop feeding your fish for at least 24-48 hours to give it time to recover from digestion problems. Make sure you pay attention to your fish’s feeding pattern to prevent overfeeding.

Excessive Gas from Floating Foods

If you provide your fish with too much food that floats on the water’s surface, it will take in more air as it eats. To prevent this from happening, you can soak food for a few seconds in the tank water, making sure it will sink before putting it in the tank.

Bacterial Infections

When bacteria makes a fish bloated and causes it to swim sideways, this is usually a sign that the fish needs help right away. Antibiotics are usually used to treat bacterial infections in a fish’s swim bladder. It is strongly suggested that you talk to a vet before treating this.

Parasites

There are a lot of parasites that find fish guts to be an ideal home. For example, callamanus worms feed by attaching themselves to a fish’s digestive system, which causes the fish to bloat and swim sideways. Most of the time, it’s hard to find these parasites in their early stages, which makes them hard to treat.

Constipation

If your fish can’t get rid of waste, it will build up in its stomach and cause it to become bloated. So much so that the pressure affects the fish’s swim bladder, which makes the fish swim sideways because it can’t properly control its swim bladder.

Can You Cure Swim Bladder Disease?

Yes—if caught early. Most cases resolve completely with proper treatment, especially those caused by diet or water quality.

Here’s the proven treatment for digestive-related swim bladder disease:

• Days 1-3: Fast completely (no food at all)
• Day 4-5: Introduce blanched, peeled green peas (high fiber promotes digestive movement)
• Temperature: Maintain water at 78-80°F to support metabolism
• Tank adjustments: Lower the water level slightly to help the fish reach the surface more easily
• Monitor: If symptoms improve, gradually resume normal feeding with high-quality, sinking food

Recovery Timeline:

• Digestive issues: 3-7 days typically show improvement
• Temporary stress: 24-48 hours once stressors are removed
• Bacterial infections: 7-14 days of antibiotic treatment
• Physical damage: Permanent condition but manageable
• Internal organ disease: May not be reversible

If symptoms don’t improve after 10 days or worsen: Consult an aquatic veterinarian. Your fish may have a more serious underlying condition requiring professional diagnosis.

How To Prevent Your Fish From Swimming Sideways

Feeding Practices (The #1 Prevention)

Feed only what your fish can eat in 2-3 minutes. Feed once or twice daily, never more. Never leave uneaten food in the tank (remove after 5 minutes). Use high-quality, species-appropriate food. Avoid exclusively feeding floating pellets or flakes—use sinking options. Pre-soak floating foods to help them sink. Fast your fish one day per week.

Water Quality Management

Change 25-30% of tank water every 7-10 days. Test water parameters weekly (ammonia, nitrite, nitrate, pH). Use a filter rated for 3-4x your tank volume per hour. Clean filter media regularly (without removing all at once). Vacuum gravel during water changes to remove waste buildup.

Tank Environment

Maintain stable water temperature (72-78°F for most tropical species). Provide hiding spots and territory markers. Avoid overcrowding (generally one inch of fish per gallon). Choose compatible tank mates with similar temperaments. Remove aggressive fish immediately if fighting occurs. Smooth any sharp decorations that could injure fish. Keep the tank in a stable, low-traffic location away from direct sunlight.

1. Occasionally Feed Green Peas

Green peas have a lot of fiber, which will keep the fish from getting constipated. They are often used to treat fish that swim sideways. You can boil green peas in a pot for a few minutes, then make sure to remove the skin before giving it to your fish.

2. Frequent Water Changes

Infections and intestinal parasites that make the fish swim sideways are mostly caused by dirty tanks, which is why it’s so important to keep your tank clean. Make sure to change your aquarium water for at least 25% per week to prevent it from becoming toxic. Remove any extra food or trash you see in the tank to give your filter a break and make it last longer.

3. Give Proper Food

If you only have dry food to give your fish, wet it first to prevent it from floating. Don’t give your fish feeds that float so they don’t gulp down too much air, which can make them bloated. Usually, a bloated swim bladder caused by gulping too much air can cause your fish to swim sideways.

4. Avoid Overfeeding

Make sure you feed your fish the right amount of food to prevent having problems with their stomachs. If you feed your fish too much, it can get bloated and constipated, which makes it swim sideways. As a general rule, you should only feed your fish what it can eat in two to three minutes.

5. Avoid Stressing Your Fish

When your fish swim sideways, it may be because they are too stressed. There are plenty of things that can stress out a fish. To prevent this from happening, don’t put your fish in a tank with too many other fish, and don’t put them in a tank with fish that like to fight. Also, don’t touch your fish, because that wouldn’t be good for them.

6. Give Your Fish A Safe Place To Swim

Sometimes, fish problems are caused by what we put in our aquariums. Fish are naturally curious, so they swim everywhere. Make sure that you prevent your fish from getting scratched by sharp edges on aquarium decorations or driftwood, which can tear off a fish’s fin and cause it to swim sideways.

Common Signs of Stress in Aquarium Fish

Understanding and identifying signs of stress in aquarium fish can be crucial in preventing health issues that may lead to symptoms like sideways swimming. Stress in fish can be caused by a variety of factors, including poor water conditions, inappropriate tank mates, or inadequate diet. Here are some key signs of stress to watch for in your aquatic pets:

1. Erratic Swimming: If you notice your fish swimming erratically or darting around the tank without apparent reason, this could be a sign of stress or discomfort within the tank environment.

2. Hiding or Withdrawal: While some fish are naturally shy, excessive hiding or a sudden change in a fish’s willingness to interact or feed can indicate that it feels threatened or stressed.

3. Changes in Appearance: Watch for changes such as faded colors, clamped fins, or spots appearing on the body. These can all be indicators of stress or illness in fish.

4. Rapid Gill Movement: Gills that move more rapidly than normal can be a sign that the fish is struggling to breathe, often due to poor water quality or a lack of oxygen.

5. Loss of Appetite: A sudden disinterest in food is a common symptom of stress or sickness in aquarium fish.

6. Aggression or Bullying: Changes in social behavior, such as increased aggression or bullying, can be a response to stress, often caused by overcrowding or incompatible tank mates.

By keeping an eye out for these signs, you can take early action to adjust the environment or care routine to reduce stress and prevent further health issues. Regular observation and quick response to signs of stress can greatly enhance the well-being of your aquatic pets.

FAQ

Can a fish recover from swimming sideways?

Yes, in many cases, especially if the cause is diet-related or environmental stress. Early intervention dramatically improves outcomes.

Should I euthanize a fish that is swimming sideways?

Only as a last resort if its quality of life is severely compromised after 10-14 days of appropriate treatment with no improvement. Most fish respond well to early care.

Is swim bladder disease contagious?

No, the condition itself is not contagious. However, if the underlying cause is a bacterial infection, that infection could spread to other fish in the tank.

Why Is Your Tetra Fish Swimming Sideways?

According to Pet Fish Online, tetras tend to swim sideways because they have a problem with their swim bladders. This makes the fish less buoyant, making it harder for tetras to swim normally, and they might even sink to the bottom. This is mostly because the water quality isn’t good enough.

Why Is Your Angelfish Swimming Sideways?

Angelfish with swim bladder disease will usually swim sideways, says Just Fish Keeping. The disorder is a disease that gets worse over time and makes the fish unable to swim properly. Most of the time, a bad swim bladder is a sign of another illness rather than a separate disorder.

Why Is Your Molly Fish Swimming Sideways?

Molly fish that swim sideways are caused by other organs pressing on the swim bladder and making it stop working. Buoyancy issues can also be caused by internal organ diseases and even eggs that are stuck together.

Why Are Your Glofish Swimming Sideways?

Most of the time, glofish swim sideways because they have swim bladder disease. A swim bladder is an organ inside bony fish that is filled with gas and helps them stay afloat. And if the fish’s bladder is affected by illness, injury, or anything else that isn’t normal, it will be hard for the fish to stay afloat, so it will swim in strange ways, like sideways.

Why Is Your Goldfish Swimming Sideways?

Swim bladder disease or disorder is almost always the cause of a goldfish swimming sideways. Even though this word is often used to describe diseases in fish, it is actually a sign of a bigger problem.

Conclusion

Swim bladder disease is frightening to witness, but it’s manageable and most cases resolve completely with early intervention focused on diet, water quality, and stress reduction.

The most important steps you can take right now:

• Stop feeding your fish
• Improve water conditions with a 25-30% water change
• Lower the water level slightly to reduce effort
• Test water parameters
• Monitor closely for improvement over the next 3-5 days

By observing your fish closely, maintaining excellent water quality, and feeding appropriate portions, you can solve this problem and prevent it from happening again. Your fish depends on you, and you’re taking the right steps by seeking information. Most fish with sideways swimming recover fully with proper care.