Why Do My Oscar Fish Keep Dying? {How Can I Prevent It?}

It’s tragic to see your oscar dying, but what is causing this? What can you do to prevent future oscar fish deaths? In this article, we’ll explore the reasons why your oscar fish keep dying.

Why Do My Oscar Fish Keep Dying? Rising ammonia levels, poor diet, infrequent water changes and their overall inability to adjust to the habitat in your aquarium is causing the death of your oscar fish. 

What can be done? The answer is, a lot. Stick around and let’s get to the bottom of this.

How Do I Know If My Oscar Fish Is Dying?

Your oscar fish will display some obvious and not so obvious symptoms that you should look out for. Here are some signs that your oscar fish is dying:

  • Staying at the surface
  • Gasping for air
  • Discoloration
  • Injured or rotting fins
  • Erratic swimming
  • Lethargic or sluggish swimming
  • Excessive hiding
  • Loss of appetite
  • Not using fins or fins stuck to their body
  • Loss of spatial awareness

Although oscar fish are resilient and hardy, they are still susceptible to many illnesses. The thing is, oscar fish create a lot of waste. Their tanks must be cleaned often with frequent water changes and many tests to make sure the water parameters are ideal.

What Types of Stress Are Unnoticeable When An Oscar Fish Is Dying?

Not all diseases or infections are noticeable upfront. Some may take time to develop as outward skin infection on their bodies, heads, fins and tail. Sometimes it’s their personality that gives it away.

Look out for your oscar acting strange. They could be facing the corner of your tank completely unaware of their surroundings. Their eyes may not be focusing on anything in particular or they could be bumping around objects or into the walls of your aquarium.

A dying oscar fish may end up disinterested in their tankmates or the food you’re offering it. This is truly unfortunate circumstances, but you can step in and try your best to keep your oscar fish alive.

What Type Of Food Should I Feed My Dying Oscar Fish?

The idea here is to ignite their appetites if they’re refusing to eat. This is a good time to put aside the healthy pellets or flakes that you spent good money on for the ideal nutrition it provides your oscar fish. They’re avoiding this food, so it doesn’t matter how healthy it is.

If they aren’t eating what you’re offering, make sure to scoop it out of the tank or you’ll be adding more waste that could turn into ammonia, which will make matters worse.

Try live foods such a worms or shrimp. They can be frozen and thawed out first, then offered as tasty snacks to hopefully intrigue your oscar fish to eat again. You may have to reduce the size of these live foods by cutting them up and making it easier for your dying oscar fish to eat.

Try soaking the live food in garlic juice or vitamin supplements in a bottle to add more flavor and nutrients that will help to boost their immune systems.

Do Gill Flukes Kill Oscar Fish?

Oscar fish are generally hardy fish and skin flukes or gill flukes are parasites that they can get rid of naturally. When your oscar fish is not eating or under stress, it will be harder to deal with common gill flukes.

Gill flukes are usually not a threat to kill your oscar fish, but in their weakened state, they become harder to handle. These parasites may slow down your oscar fish even further and contribute to their eventual death.

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Are The Other Fish In My Tank Killing My Oscar Fish?

The two major negative factors in housing your oscar fish with tankmates are the following:

  • Aggression
  • Competition


Oscar fish are territorial and they will defend their space against tankmates. They can grow larger in size compared to other fish in your aquarium and they’ll use this size to bump and chase away other fish in their area. Too much aggression can lead to:

  • fin nipping
  • wounds
  • abrasions
  • infections

Once your oscar fish is wounded, there will be a higher chance that parasites, unhealthy bacteria or ammonia in the tank cause more damage to them. Their immune systems may weaken and death may result.


If there are overcrowding issues or competition is rife in the tank, there may end up being food wars. Food scarcity may result even though you’re feeding adequate amounts of food to all your fish on schedule.

If your oscar fish is constantly in competition for food, they may give up the fight. Adult oscar fish can go a month without eating and juveniles can last up to 2 weeks. The lack of eating will contribute to a loss of appetite and energy. The lack of nutrition will weaken your oscar fish.

Why is My Oscar Fish Looking Lost? Is it Dying?

One glaring sign of a sick or dying oscar fish is when they aren’t swimming in their normal way. It could be lethargic swimming or erratic movements. Sometimes they just look lost.

Oscar fish usually swim in the middle or top level of your tank. They may swim low to find food or lie on their side for short periods. All of this is normal.

The problem lies when your oscar fish don’t resume their normal swimming habits after swimming low or resting. They are too slow to spring back to the middle of the tank or unaware of their location in the tank.

My Oscar Fish Is Struggling To Breath. What Can I Do?

Watch and observe the gills of your oscar fish carefully. They must move at a steady pace to allow for the flow of blood through it in the opposite directions of the moving water. They are ridding themselves of toxins and increasing their intake of oxygen.

If they are breathing faster or slower, then there is something wrong. You may even notice that mucus is secreting out of their gills as a mechanism for protection. The water could be filling up with unwanted amounts of:

  • bacteria
  • fungus
  • parasites
  • nitrites
  • nitrates
  • ammonia

All of this will harm your oscar fish if they aren’t breathing well. It’s time for major water changes at 50-75% 2-3 times a week at least while testing the water to keep the parameters ideal.

How Do I Reduce The Stress In My Oscar Fish To Prevent It From Dying?

A stressed oscar fish is much more likely to become ill from external factors than a healthy one. The aquarium is a contained ecosystem that you are managing. Changes and fluctuations can and will occur from time to time. Mistakes and oversights can be made.

We’re hoping your oscar fish are hardy enough to handle to imperfections in the tank from time to time. Slight changes in water temperature could alter their behavior and cause enough stress to throw off their immune systems.

Our strongest skill as fishkeepers is our ability to watch and observe acutely to notice if our oscar fish are acting strange. Then we test the water and act accordingly. We may also have to move around tankmates that are stressing each other out.

Is My Tank The Reason Why My Oscar Fish Are Dying?

Sometimes we bring sick fish home without even knowing it. We are fighting an uphill battle from the get go. In most cases, the fish are healthy and our tank still isn’t right for them. Make sure to research and check if the following parameters are in place for your oscar fish to thrive:

  • suitable tankmates
  • ammonia levels at 0
  • pH balance between 6.0-8.0
  • water hardness 12dH-15dH
  • temperature at 75-80°F
  • 75 gallon tank or larger
  • strong filtration


Oscar fish create a lot of waste and need proper filtration and plenty of water changes to survive in your tank. Testing the water is crucial to keep ammonia levels at 0. If they are breathing excess ammonia from their waste or food debris, it will harm their gills and lead to illness or death.

Clean the tank and clean the filter frequently. Vacuum the substrate often. Avoid adding aquarium salt because your oscar fish don’t respond well to it.

Your tank can and will become a great place for your oscar fish to thrive. Be patient and do your best to keep it clean. We wish you and your oscar fish the best of luck!

Brian Arial

Brian Arial has kept fish for leisure and worked with fish stores for most of his life. He enjoys writing and caring for aquariums and ponds.