Hole in the Head Disease

Hole in the Head Disease
Written by Oscar

Hole in the Head Disease is probably the most feared disease amongst people who keep Oscar fish. Hole in the Head Disease is not always fatal if caught early and treated. However, it can often leave terrible scarring on the fishes head which may be permanent after the disease has healed.


Hole in the Head Disease is relatively easy to diagnose. In its very early stages, you may notice one or two small holes appearing on the fish’s head. Often the holes are very symmetrical, almost as if somebody has stuck a dart into the Oscars skin. If left these holes will gradually get bigger and grow in number. Holes and lesions may spread to the mouth area, around the gills and eyes. In severe cases, the lateral line may start eroding. Once the condition becomes very bad, you may notice stringy mucus trailing from the wounds, people often mistake these for worms. The fish may well go off its food and develop a hollow-bellied appearance.

Hole in the Head Disease is curable, but more importantly, it is perfectly preventable. Regular tank maintenance, i.e. water changes, removing solid debris from the tank and filtration system will help keep the water in good condition. Good water conditions are the key to preventing Hole in the Head Disease in Oscar Fish.

Treating HITH

If you notice Hole Head Disease developing then act quickly by first testing the quality of your aquarium water. Carry out an ammonia, nitrite, nitrate and pH test, preferably using a liquid test kit. In the majority of cases hole in the head disease is brought on by poor water conditions, it is extremely uncommon for fish to develop this disease for no reason. However, because stress is the main cause of hole in the head disease it could have been caused by the fish being exposed to large fluctuations in water temperature, normally occurring when water changes are carried out. If you discover that you have indeed got poor water conditions then you must act accordingly by carrying out a large water change to remove as much of the toxin as possible. You may also be wise to get a product called “Prime”. This product not only removes chlorine but also detoxifies ammonia and nitrite. One thing to remember when using these chemicals that “remove” ammonia is that they don’t actually remove ammonia, what they do is detoxify the ammonia and turn it into ammonium which is a less toxic form of ammonia. Therefore, when you carry out a water test, you will still get a reading for ammonia, but you will actually be testing ammonium which is much much less harmful to fish. Carry out water changes until your ammonia and/or nitrite are back to zero and stay like that.

Nitrate is a byproduct of ammonia and nitrite. Whereas it is nowhere near as toxic as ammonia or nitrite, it must be kept as low as possible. Very high levels of nitrate will cause stress to your fish which in turn can bring on disease and illness such as Hole in the Head Disease. We do not recommend letting your nitrate exceed 40 ppm. Regular water changes will help keep nitrate levels low.

Early stages of Hole in the Head Disease can be cured by simply increasing your tank maintenance and water changes making sure that there is no toxins present, and your nitrate is always low. Severe cases of hole in the head disease may need intervention from medication. One of the most recognised treatments for Hole in the Head is a medication called Metronidazole. Metronidazole comes in tablets and powder form and is also part of the ingredients of some medication.


Hexamita parasites are what cause Hole in the Head Disease. They are best treated using a medication called  which needs to be obtained under prescription in the UK if bought in tablet form. This medication needs to be ingested by the fish, it can’t simply be added to the tank like other medications. Obviously, a fish is not going to simply eat these tablets, you will have to mix the medication with food so the fish will readily eat it. There are various ways to prepare Metronidazole so that it can be easily fed to your fish.

Your veterinarian should prescribe you Metronidazole in tablet form which you will then need to crush into powder form. I would rather not give you exact measurements as this is a job for your veterinarian. However, if you don’t need a prescription and you can buy this medication off-the-shelf then they should come with detailed instructions on how much to use. If you are still confused then visit our community forum for advice. There are a couple of ways to prepare your food, one way is to take some frozen food, partially thaw it, mix the powder mix with the partially frozen food and then refreeze it. Once it is frozen it is ready to feed to your fish. Another way to prepare your medication is to use dried pellets food, crush them using a mortar and pestle until the pellets are in the form of fine powder. Then take your Metronidazole tablets and crush them into powder. To bind them back together you can use gelatin which can be purchased from most food stores. You will have to mix the gelatin and tablet powder together until you have the consistency of firm paste. Roll the pellets into balls that resemble the food size that you feed your fish. Don’t make them too big or the fish might struggle to eat them. It should only take half an hour for the pellets to set, after this, they are ready to feed to your fish. So you should feed your fish for a minimum of one week on this food type, do not feed your fish any other type of food during this period of medication.

If you are in the UK then there is a product called .This medication comes in tablet form and you treat your tank over a number of days, these tablets are not meant to be ingested so don’t prepare them the same way as Metronidazole. I can’t really give you any kind of guarantee that this medication will work, but it’s always worth trying.

A Healthy Diet

One theory put forward is that a poor diet lacking in vitamins contributes to the development of hole in the head disease. An unhealthy diet weakens the fishes immune system which can then allow the Hexamita parasites to become more troublesome. Feeding your Oscar on a healthy diet is very important if you want to keep it healthy. A good quality pellet feed will contain all the vitamins your Oscar needs so this should be the staple part of its diet. A lot of people give their Oscar fish live foods such as goldfish, aka feeders, these are unsafe and should not be part of your Oscars diet. Feeders are often bred in large numbers and are not taken care of, they often harbour disease which can be passed onto your Oscar. Feeding your Oscar greens as part of its diet is recommended. Try peas, pieces of courgette, even carrots if your Oscar will accept them. If your Oscar won’t eat vegetables then the easiest way to introduce vitamins into their diet is to feed them foods such as earthworms, snails, shrimps, prawns, mealworms, cockles and mussels. All of these are readily available from the fish store, supermarket, fishmongers, pet shop, or you can even harvest some of these foods from your garden.


Most good quality fish foods contain all of the vitamins that your fish require. However, it wouldn’t hurt to give them a few extra vitamins whilst you are treating them. With some vitamins, you can add a few drops to the aquarium water every day, or if you want to make sure that the fish are getting the vitamins, try soaking the food in some liquid vitamin. You can soak various foods such as bloodworm, meal worms, pellets and probably even worms. How much difference extra vitamins will make is something I cannot answer, but it is certainly not going to do your fish any harm.

Unfortunately, due to the fact that many people do not keep Oscars in the correct environment, hole in the head disease is all too common and we often get people seeking help on the forums. Oscar Fish can get quite big, they produce lots of waste and create large amounts of ammonia. If you do not provide them with the correct living conditions, i.e. a large aquarium, a healthy diet and plenty of filtration, it is inevitable that you will be putting your fish at great risk from developing not only hole in the head disease but many other disease and illnesses as well.

Sensory pits

I think it’s worth mentioning an Oscars “sensory pits”. Lots of people suddenly notice tiny little pinprick holes when they are observing their Oscar close up, or when they are looking at a photograph that has been taken using the flash. They then start panicking because they think their Oscar is developing hole in the head disease. Worry not, these are sensory pits and are totally normal, they should not be confused with hole in the head disease. The excellent photograph above provided by Rafel, one of our members clearly shows lots of pinprick holes arranged in circles, these are the sensory pits.

About the author