Today, you will learn about the common diseases that affect Oscars.
Is your Oscar sick, and you’re trying to figure out what is wrong? Or are you about ready to purchase one and trying to learn about the common diseases that affect them?
Either way, you are in the right place! Below, I go over TEN of the most common ailments that can affect Oscars. In addition, you will learn the underlying cause of each illness and HOW to treat the problem.
And before you go, scroll to the bottom to learn how to easily prevent most diseases on this list!
*I wasn’t able to get pictures that show Oscars displaying each of the common diseases below. But I did my best to show examples of what each illness looks like.*
#1. Dropsy
Symptoms:
- Dropsy is a condition where fluid accumulates inside the body cavity and tissues of Oscar.
- As a result, your fish will have a hugely swollen belly that seems like it has “dropped down.”
- Other symptoms include protruding scales, ulcers, and reddening at the base of fins or vent.
What causes Dropsy?
- Dropsy is actually a name for the symptoms that your fish experiences, as Dropsy can be caused by several underlying things.
- Viral and bacterial infections, parasites, poor water conditions, sudden changes in temperature, stress, improper nutrition, or overcrowding are all underlying causes.
How do you treat Dropsy?
- Since it’s hard to know what caused this disease, treating the infected Oscar can be difficult.
- To prevent the spread of Dropsy, you should immediately remove the affected individual to a separate tank and make sure the water quality is perfect, along with providing excellent food. Then treat the aquarium with an antibacterial, such as API PIMAFIX Antifungal.
- You can also try using salt since bacteria and fungi are not able to tolerate it. This API Aquarium Salt works well, but you need to be careful when applying and not add too much! API recommends adding 1 rounded tablespoon for every 5 gallons of water. So if you have a 55-gallon tank, that would be 11 tablespoons of salt, but they do say to be careful if you have live plants, as some are sensitive to salt.
- I would also do a water change on the original tank and monitor it VERY closely for further infections.
Unfortunately, unless you detect Dropsy early, it’s most likely a death sentence for your Oscar. As soon as you notice this disease, you must take immediate action to try and save the fish. Keeping your tank clean, not overfeeding, and not overcrowding are the best ways to prevent Dropsy.
#2. Hole-in-the-head Disease (Hexamitiasis)
Symptoms:
- Small holes appear on the Oscar body, especially near their head. These holes eventually turn into tubular eruptions. It sort of looks like something is eating the fish alive.
- Yellow strings of mucus that sort of look like worms often trail from the holes. This symptom has confused many people into thinking their Oscar was infested with worms.
- Sick fish will often stop eating. Their face is also more subdued than normal.
What causes Hole-in-the-head Disease?
- The cause of this illness is unclear, but flagellate protozoans (Hexamita or Sprionucleus) have been involved in the past.
- It’s common for many fish to have low-level infections of Hexamita in their intestines without doing the fish any harm. But certain factors, such as poor nutrition, overcrowding, low oxygen levels, bad water condition, or any other stressor, cause the parasites to multiply and develop into Hole-in-the-head Disease.
How do you treat Hole-in-the-head Disease?
- Using medicated fish food is a great way to treat this illness. Unfortunately, most affected Oscars have stopped eating, and it can be hard to mix medicated food on a small scale.
- Adding the drug metronidazole, which is designed to fight protozoan parasites like Hexamita, directly to the tank also works. Follow the directions closely to get the dosage correct.
To prevent Hole-in-the-head Disease, make sure to quarantine all new fish. Also, eliminate the contributing factors, such as poor water quality. When testing your water, aim for a nitrate concentration of less than 20 mg/l. Make sure not to overfeed and do a partial water change weekly.
#3. Ich (Also called White Spot Disease)
Symptoms:
- Small, white spots on the gills, skin, and fins. The Oscars will look like it has been sprinkled with salt.
- If the fish is heavily infected, the spots may combine to form irregular white patches.
- Fish may scratch against gravel and rocks or show increased gill movements.
- Did you recently add new fish to your tank without quarantining them? If so, one of them was likely carrying the parasite.
What causes Ich?
- The ciliate protozoan Ichthyophthirius multifiliis causes this disease in Oscars. Each of the white spots you see are individual parasites located just beneath the fish’s transparent skin.
- New fish added to your tank are the main culprit for an Ich infestation, so it’s imperative that you quarantine them for a few weeks until you know they are healthy.
How do you treat Ich?
- There are many effective treatments commercially available that work well.
- I have personally used API Liquid Super Ick Cure before. First, remove activated carbon from the filter, and then add 1 teaspoon for every 5 gallons of aquarium water. Repeat the dose after 48 hours and then change 25% of the water.
- You should also increase the water temperature to as high as 82 degrees Fahrenheit. The warmer the water, the faster the life cycle of the parasite progresses. Specifically, the little white spots on your fish eventually mature, break through the skin, and fall to the aquarium floor. The Ich treatment you added only works on the parasites that are free-swimming in the water, so you need them to get into the water while it’s being medicated to kill them.
Ich is very common and one of the only fish parasites you can see with your naked eye. As long as you catch the symptoms early and start treatment right away, then you should be able to save your Oscar. If you don’t intervene, then it will likely die.
#4. Physical damage
Symptoms:
- Damage to the body or mouth. Open wounds.
- Split or damaged fins. Loss of scales but with normal coloration.
- Loss of an eye. Fish commonly attack another individual’s eyes.
What causes physical damage?
- The most common cause is an aggressive fish that attacks their tank mates.
- Oscar can also be hurt when tangled in a net or not handled carefully.
How do you treat physical damage?
- Put hurt fish into a separate tank and treat with an antibacterial. Give them plenty of time to heal fully.
- Adding salt to the water also helps heal the wounds quicker.
- You must discover the cause of the damage. Observe your fish until you can find which one is attacking the others. You don’t want to fix a hurt fish only to put it back into the same environment!
#5. Fin Rot
Symptoms:
- Stumpy, frayed, ragged, or split fins.
- The fin often has a white edge (black or brown in some cases) on them.
- Fin Rot often appears simultaneously as Cotton-Wool Disease (#10) since they can both be caused by the Flavobacterium bacteria.
What causes Fin Rot?
- Bacteria, such as Flavobacterium, Aeromonas, and Pseudomonas, are typically to blame.
- Fin Rot typically affects Oscars that are in poor condition for some reason. For example, fighting (fin nipping), poor water conditions, poor nutrition, overcrowding, overfeeding, or new fish that were handled roughly can lead to Fin Rot.
How do you treat Fin Rot?
- Move the infected individual to a separate treatment tank. If all the fish show symptoms, this step is unnecessary, and you can treat all the fish together.
- Infections are relatively easy to cure. Treat your aquarium with an antibacterial, such as API PIMAFIX Antifungal.
- You can also try using salt since bacteria can’t tolerate it. This API Aquarium Salt works well, but you need to be careful when applying and not add too much! API recommends adding 1 rounded tablespoon for every 5 gallons of water. So if you have a 55-gallon tank, that would be 11 tablespoons of salt, but they do say to be careful if you have live plants, as some are sensitive to salt.
- Check your Oscar every day to see if the Fin Rot has ceased. Once cured, you will see the fins and tail slowly start to grow back!
Luckily, if you act right away, you should be able to cure your fish of Fin Rot. But you need to try and figure out what was the underlying cause of the illness. Is your tank overcrowded? Is your water quality poor? No matter what, I would do a partial water change immediately and test your water.
#6. Gill disease
Symptoms:
- Swollen gills, discolored gill filaments with excess mucous, or rapid gill movements.
- Not eating.
- Fish is gasping at the surface or lying motionless.
What causes problems in the gills?
- Poor water conditions, such as toxic levels of ammonia or chlorine, poor filtration, poor aeration, or overcrowding.
- Infections from bacteria, protozoans, monogenetic flukes (parasites), or fungi (like Branchiomyces).
- Newly added Oscars are especially susceptible to gill problems.
How do you treat gill disease?
- First, test the water to see if there is a water quality problem, such as too much ammonia. If so, make a 25-50 percent partial water change. Don’t use unconditioned tap water since it may irritate the gill membranes even more.
- If changing and improving the water didn’t help, move the diseased Oscar to an isolation tank. Then, add an antibacterial treatment to the water, such as API PIMAFIX Antifungal.
- If your fish STILL appears sick, then the disease might be from gill parasites. In this case, you will need to use a copper treatment or an organophosphorus insecticide like formalin or metrifonate. However, these treatments can be harmful to some scaleless fish and invertebrates, so you must treat the infected fish in a separate tank.
Once again, the best way to prevent this disease is to ensure you keep a healthy tank. You should regularly test the water for problems, do partial water changes regularly, keep it clean, feed nutritious food (but not too much), and not overcrowd.
#7. Fish Tuberculosis (Wasting Disease)
Symptoms:
- Fish will look emaciated and hollow-bellied and appear lethargic.
- Loss of appetite and loss of color. Ulcers, fin rot, and “pop-eye” are also common.
- Small nodules, which are about the size of a pinhead, also appear on the internal organs.
What causes Fish Tuberculosis?
- Acid-fast bacteria, such as Nocardia or Mycobacterium, are responsible.
- This disease is thought to be passed from fish to fish by feeding on material that is already infected. For example, this can happen when feeding a fish with an infected feeder fish or when a fish dies in the tank, and other fish take nibbles from the corpse.
- Healthy Oscar can have the infection but never show signs of the disease unless environmental conditions change. For example, poor water quality and stress often cause an outbreak.
How do you treat Fish Tuberculosis?
- Unfortunately, there is no cure for this disease.
- If there are other fish in the tank, you should assume that they all have contracted Fish Tuberculosis. Therefore, you need to treat this tank as a closed system, not adding new fish nor taking out any fish, water, or plants to use elsewhere.
- Some fish can live a long time with the infection and show no symptoms. But if you have a tank full of fish, you may notice sudden, random deaths over time.
Fish Tuberculosis is one of the few fish diseases that can be transferred to humans, which typically causes a persistent rash on the hands and fingers. It is ESSENTIAL to avoid contact with an infected fish or contaminated water on any open wounds. Make sure to disinfect equipment that has also been exposed.
If you think you have been exposed, please seek medical attention to see what they recommend.
#8. Popeye Disease (Also called Exophthalmia)
Symptoms:
- One or both eyes pop out of the head in an unusual way, hence the name of the disease. The eye protrudes due to water build-up either behind or in the eye.
- The eyes may appear cloudy but often stay clear.
What causes Popeye Disease?
- One or more factors may be involved, including parasites, bacterial infection, and poor water quality.
- If only one eye is swollen and looks puffy, it’s possible another fish just injured it.
How do you treat Popeye Disease?
- Assuming it’s a bacterial infection, then move the fish to an isolation tank, so it doesn’t affect anyone else. Then, treat with a broad-based antibiotic like API General Cure.
- The quicker you can provide treatment; the more likely your Oscar will survive!
- If you suspect another fish may have just injured the eye, then treat the tank with aquarium salt, which will help the fish heal faster.
To stop Popeye Disease or prevent it from happening, it’s essential to get the water conditions as optimal as possible. So test your water immediately, and make sure to feed a varied, healthy diet.
#9. Swim bladder disorders
Symptoms:
- In general, your fish will have a floating problem and have difficulty maintaining its water position. It may float on its side or at the surface or even remain sunk on the bottom.
- Other than not being able to float property, the fish typically looks in good condition.
What causes a swim bladder disorder?
- The exact causes are poorly understood.
- There are thought to be various factors that can cause problems with the swim bladder, including microbial infections and sudden temperature changes.
- Swim bladder disorders even seem to happen spontaneously in healthy fish, and it’s common for other fish in the tank to remain unaffected.
How do you treat a swim bladder disorder?
- Executing a reliable treatment is challenging since the exact cause of the disease is not known.
- Try treating the tank with aquarium salt or an antibiotic remedy. This treatment should help if the cause is an infection.
- Try raising the temperature to 80 degrees Fahrenheit (27 C) and then don’t feed the fish for three days. Sometimes low water temperature can slow the digestive process, which puts undue pressure on the swim bladder.
You can also make the Oscars more comfortable by lowering the water level, which lets it move around easier. Unfortunately, if the sick fish isn’t getting better and unable to eat, it might have to be put down to avoid needless suffering.
#10. Cotton-Wool Disease (Mouth Fungus)
Symptoms:
- The first signs of the disease usually appear on the mouth as off-white marks around the Oscar fins, body, or mouth.
- As the infection progresses, white cotton-wool growths (hence the name) will typically appear around the mouth or other parts of the body.
- Most infected Oscars often stop eating and start to appear thin, but these symptoms usually appear AFTER the cotton-wool growths are already apparent. The problem with Cotton Wool Disease is that fish don’t act differently until the “cotton wool” marks start appearing on their skin.
What causes Cotton-Wool Disease?
- Normally, Flavobacterium is to blame, but Cotton-Wool Disease is a general name for any fungus that eventually grows white, tufty growths on fish..
- This disease is common for NEW fish that are put in POOR water conditions.
- Sudden water quality changes or temperature increases can trigger an infection in healthy fish.
- Overall poor water quality with infrequent water changes and overstocking an aquarium can also cause Cotton-Wool Disease.
How do you treat Cotton-Wool Disease?
- If you notice the symptoms early enough, the infections are relatively easy to cure. Treat your aquarium with an antibacterial, such as API PIMAFIX Antifungal.
- You can also try using salt since fungi are not able to tolerate it. This API Aquarium Salt works well, but you need to be careful when applying and not add too much! API recommends adding 1 rounded tablespoon for every 5 gallons of water. So if you have a 55-gallon tank, that would be 11 tablespoons of salt, but they do say to be careful if you have live plants, as some are sensitive to salt.
- The fungus is contagious, so try to separate the infected fish if possible.
- Lastly, as we discussed earlier, Cotton-Wool Disease typically affects Oscars that are in poor water quality. If this describes your tank, this should be a wake-up call to keep it clean or reduce the number of fish (or both). I would also test the water immediately to look for issues!
Luckily, if you treat Cotton-Wool Disease as soon as you notice it, you should be able to save your Oscar!
Here is how you can prevent almost every Oscar disease!
I’m not sure if you noticed, but basically, every illness and ailment listed above is caused by the same few things.
If you missed it, here is what you need to do to make sure your Oscar stay healthy.
- Quarantine new fish for a few weeks before adding them to an existing tank.
- Test your water every week to look for issues. You must maintain excellent water quality to keep diseases away. If there are any imbalances, you need to address them immediately.
- Do not overcrowd your tank! Too many fish causes stress and too much waste, which then causes illness.
- Perform a 25% partial water change every two weeks. Clean the gravel as well to remove excess waste.
- Don’t overfeed your fish. Only feed them what they can eat within a few minutes.
Have you had any other Oscar diseases or illnesses?
Please share what happened below!