Skip to Content

5 Common Oscar Fish Diseases and Illnesses

5 Common Oscar Fish Diseases and Illnesses

This post is written to the author's best knowledge and is not intended to be used in place of veterinary advice. In addtion, this post may contain affiliate links. As an Amazon Associate I earn from qualifying purchases.

You need to make sure that all of the fish in your tank stay healthy. Doing your best to maintain the tank helps to keep fish in good health.

Things can still go wrong even when you do a good job as a fish tank owner, though. Oscar fish are hardy fish that are fairly easy to take care of, but they still have various diseases and illnesses that they might have to deal with.

Continue reading to learn about various Oscar fish diseases and illnesses. This will give you an idea of the problems that you should be looking out for.

If you notice any signs of these diseases or illnesses, you’ll want to take action as soon as you can. Some of the illnesses below will have the potential to kill your Oscars.

1 – Fin Rot/Tail Rot

Patriot Betta With Fin Rot
Patriot Betta With Fin Rot

Fin rot is caused by a bacterial infection. Tail rot is essentially the same thing, but it’s going to be an infection near the tail of the fish rather than the fins.

There are many different bacteria that are associated with this common disease. Some of the bacteria are likely present in the fish tank most of the time.

Healthy fish generally don’t have much to fear. It’s only when fish become stressed and develop compromised immune systems that this will become a problem.

When fish are kept in poor water conditions, they will become stressed. This will make them susceptible to infections and illnesses.

You might not have cleaned the fish tank very well. Perhaps you haven’t been doing water changes or you forgot to test the pH balance of the water.

When the water conditions are poor, it’ll make it so that fish will be very stressed. The fish might become infected by bacteria during this time.

The bacteria could have already been present in the tank. It also might have been transferred to the tank when you brought a new fish in or added a new aquatic plant.

When a fish has fin rot or tail rot, you’re going to see that parts of the fish will begin to look terrible. For example, the fins might become tattered, blackened, and bloodied.

The same thing can happen to the tail area. Sometimes, portions of the tail or the fins will fall off of the fish completely.

It will appear as if the fins or the tail are rotting away. There are other symptoms to look out for, too.

You might notice that the fish is slimier than usual. It’ll likely become very lethargic and it’ll stop eating while it’s sick.

Oscars often spend more time near the surface of the water when they have fin rot or tail rot. You should treat the fish right away to get it back to being healthy.

This is a treatable condition and it’s easier to treat the fish when you catch things fast. Antibiotics can clear up the infection and help the fish to feel better.

You’ll also need to do an immediate 30% water change to try to get rid of the bacteria. Focus on keeping the tank very clean and do your best to feed the fish high-quality fish food.

Aquarium salt is handy when treating this condition as well. Follow the directions and be sure not to add more than the directions tell you to.

Sometimes this condition will leave fish permanently disfigured. However, there is a chance that some fins will grow back.

2 – Hole in the Head Disease

Hole in the Head Disease on Purple Tang
Hole in the Head Disease on Purple Tang

Hole in the head disease is an even more serious problem than fin rot. This is a potential deadly disease that you’ll want to treat as soon as possible.

It’s a condition that is caused by a parasite. Not a lot is known about this disease at this point in time, but it’s common among many popular aquarium fish.

The belief is that it is at least partially caused by a parasite known as Hexamita. The presence of this parasite seems to be the catalyst of the disease.

It’s very possible that other things will play a part in causing Oscar fish to develop this condition. Significant stress issues, vitamin and mineral imbalances, water quality issues, and living in a tank that’s too small might be partially to blame.

Preventing this disease is about taking care of the fish tank well. You want to keep the water clean and keep your fish properly fed.

When fish develop hole in the head disease, they’re going to experience many symptoms. The most prevalent one involves lesions appearing on the head.

You might notice lesions in various spots on the top of the head and even near the eyes. These lesions have the potential to be bloody as well.

Eventually, you might see pitted lesions appear on the fish near the lateral line. The holes will become larger and more problematic as the disease progresses.

Mucous will likely be seen coming from the holes. While the fish is sick, it’s not going to have much of an appetite and it may also be lethargic.

If you don’t treat the fish, it’s going to die. Often, fish die due to secondary infections. The various lesions might become infected by bacteria and the fish will wind up dying due to being severely infected in several spots.

Treating this disease typically involves using a medication known as metronidazole. You add this directly to the water to help the fish get better.

Formalin baths or dips might also help to improve the condition of the Oscar fish. Sometimes medicated fish food is used as well.

Generally, the treatment will take at least five days. It could take up to ten days for the fish to get better.

It’s also possible that the fish might not survive despite your best efforts. If you caught the problem too late, you might wind up losing the fish.

3 – Popeye Disease

Goldfish with Popeye
Goldfish with Popeye

Popeye is a type of infection that causes severe swelling of the eyes. The swelling causes the eyes to protrude from the head of the fish.

This is a disease that can impact one or both eyes. Typically, this is only going to happen to fish when they’re kept in very poor water conditions.

The poor condition of the water makes the fish susceptible. An Oscar fish might become infected due to the dirty water and then you’ll see its eyes bulging.

It’s important to note that physical injuries can cause the same thing to occur. Fighting or ramming into an object in the tank can also cause issues with bulging eyes.

To see if a fish has popeye disease, look to see if its eyes are bulging. The Oscar fish will have a bulging or swollen eye if it is dealing with this condition.

The eye might also have a cloudy appearance. This will be very obvious if only one of the eyes is impacted.

Sadly, if you don’t treat this issue the Oscar fish might go blind. It could lose its sight or even lose the eye entirely.

To start treating this issue, it’s best to fix any problems with the water quality in the tank. Ensure that the water is clean and that the parameters are in the right range.

Endeavor to do a good job cleaning the tank and do regular water changes. Try to avoid putting your fish in a bad spot due to tank maintenance issues.

Antibiotic medications can be used to treat the infection. It should help to clear things up in a number of days.

Aquarium salt is a good choice when you’re trying to help the fish get better. This can speed up the healing process a bit.

Just don’t use more of it than you’re supposed to. So long as you follow the instructions that come with the aquarium salt, it’ll be easy to get good results.

If your fish was injured by fighting another fish, you should separate the fish. Put the injured fish in a quarantine tank until it gets better.

Hopefully, you’ll catch this issue fast enough to help the fish get better. If you’re a bit late, it could lead to blindness or the loss of an eye.

4 – Ich

Freshwater Angelfish With White Spots Indicative of Ich Disease
Freshwater Angelfish With White Spots Indicative of Ich Disease

Ich is also referred to as white spot disease in many circles. When Oscar fish get this problem, it causes white spots to appear all over their bodies.

The white spots are caused by parasites that dig under the skin of the fish. Although, the white spots that you see are actually cysts and not the parasites themselves.

Commonly, this condition is caused by poor water conditions. Fish become susceptible to infection when the water quality is bad.

The direct cause of the infection is a parasite. Parasites will multiply and more and more white spots will appear on the fish.

Just a few white spots might be noticeable at first. Soon enough, the entire body will be covered in them.

This is a highly contagious condition as well. It’s very likely that the whole fish tank will get ich if one fish has it.

If you catch things very early, you might be able to stop the spread by putting the infected fish in a quarantine tank. Often, this won’t help due to how contagious ich is.

Fish who have ich will develop the aforementioned white spots. They’ll also become very lethargic and stop eating.

It’s normal for fish who have ich to rub up against objects in the tank. It’s thought that the fish do this to try to get the parasites off of their bodies.

You might see that the fish will have red fins as the disease progresses. They might start having a tough time breathing, too.

White spots on the gills will make it very hard for the fish to breathe normally. You might see the Oscar fish just sitting at the bottom of the tank due to being sick.

Luckily, this condition is very treatable. You can treat this condition with medication that can be purchased from pet stores.

There are many ich medications out there that will get rid of the parasites. You should do some other things along with using the medicine to get the best results, though.

Raise the temperature in the fish tank to 82 degrees Fahrenheit. Warmer temperatures make the life cycles of the parasites go by faster.

It makes it easier for the medicine to kill the parasites since they won’t remain buried under the skin of the fish for nearly as long. Do this in conjunction with using aquarium salt.

The fish should make a full recovery if you do things right. Try to keep the fish tank clean so you won’t be as likely to have to deal with this again.

5 – Swim Bladder Disease

Oranda Goldfish Near Surface With Swim Bladder Issue
Oranda Goldfish Near Surface With Swim Bladder Issue

Swim bladder disease is a fairly common issue with these fish. This is because Oscars will often keep eating when they shouldn’t.

Typically, swim bladder disease is caused by fish overrating. They eat too much and then they wind up becoming constipated.

The constipation causes the swim bladder to malfunction. A swim bladder is an organ that most fish possess.

This organ is responsible for helping fish to swim by controlling buoyancy. It’s a gas-filled sac that inflates and deflates.

When a fish becomes bloated, it’ll have a huge belly that presses against the swim bladder. This prevents the swim bladder from being able to fill with gas properly.

Thus, the fish will be unable to swim around as usual. You might notice the Oscar fish swimming upside down or moving around in circles.

Sometimes fish don’t move much at all when they’re experiencing swim bladder issues. Thankfully, this is easy to solve if constipation is to blame.

You can feed the fish boiled peas to try to encourage easier defecation. Sometimes withholding food is enough to clear up the problem, too.

Swim bladder disease can be caused by intestinal infections as well. Such an infection could cause swelling in the abdominal region that will lead to issues.

In this case, treating the fish with antibiotics will be the appropriate action. When the infection clears up, the swelling should go away and the fish will feel better.

Physical injuries can also cause swim bladder issues. These might heal on their own.

If a physical injury is permanent, it might cause the swim bladder issue to be permanent as well. In this case, it’s usually humane to euthanize the fish.

You can discuss this with an exotic veterinarian. They can help you to make the best decision for your fish.