Hole in the Head Fish Disease – Prevention and Treatment!

Charlie Morton

Charlie Morton


Hole in the Head Fish

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Hole in the head and lateral line erosion (HLLE) disease are two fairly synonymous common diseases that can cause distress not only to your aquarium fish but also for you to witness.

The sudden appearance of unsightly lesions and holes forming on your fish is never going to be a comfortable experience for either of you.

Luckily, there are several ways to prevent and treat the illness – and it all has to do with following some of the fundamental principles of good fish keeping.

What Is Hole In The Head Fish?

Hole in the head and lateral line erosion disease (HLLE) is a mysterious ailment present in all types of aquarium and pond fish. As the name suggests, it involves holes forming on a fish’s head and lesions across the lateral line sensory system on a fish’s flanks.

It occurs much more readily in pet fish and on fish farms than in wild populations which leads us to believe it’s caused by unnatural stress factors associated with fish keeping.

What Is The Lateral Line In Fish?

The lateral line is a sensory system that gives fish the ability to sense subtle water motion and pressure gradients. It is made up of many tiny sensory structures known as neuromasts that collect information about the water environment.

These make up an important part of a fish’s sensory perception. It may help to think about the lateral line as a fish’s sixth sense, and it can be badly affected by lateral line disease.

Which Species Of Fish Are Most At Risk From Hole In The Head Disease?

Hole-in-the-head disease can affect all kinds of freshwater and saltwater fish but is especially common in certain fish species. Cichlids such as discus and oscars are particularly famous for contracting holes in their heads and this is one of the reasons that these fish are recommended for experienced fish keepers only.

In coldwater freshwater fish, goldfish and carp are also commonly affected by the disease, and in marine tanks, angelfish and surgeonfish are particularly susceptible.

Symptoms of Hole In The Head Disease

Symptoms of hole in the head disease include lesions, depressions, and even small holes around the head and lateral lines of an infected fish. The spots or holes can vary greatly in color, size, and depth, and in more severe cases, may trail pus or mucus.

Fish affected by hole in the head and HLLE will also often turn a pale color and may excrete pale feces.

Since the lateral line is an important sensory and orienting organ in fish, fish affected with the disease may become giddy, losing their balance and twitching. Tilted swimming and even seizures are possible signs that a fish is affected.

As with many other diseases, the affected fish may also become unresponsive, lethargic, and uninterested in food.

Causes of Hole In The Head Disease In Fish

There have been many theories for what can cause hole in the head disease, but in reality, it’s still unknown. A scientific report in 2016 concluded that there was still no firm evidence about a single cause for hole in the head.

The report cites multiple possible causes for the disease including stress, infection with pathogenic agents, activated carbon, water composition, malnutrition, lack of ultraviolet light, stray current, and the uptake of copper.

It’s true that there is a fairly firm link established between Hexamitiasis parasites and HLLE, with the idea being that the parasite causes lesions on the head and flanks of the fish which are followed up with secondary infections from bacteria and fungi pathogens.

But it’s important to understand that Hexamitiasis parasites are common and may be present in healthy fish without them showing any sign of illness. Like many pathogens, it can be present in the aquarium and lie dormant until a weakness appears in a fish for it to strike and cause illness.


The most useful cause to understand in regards to hole in the head disease is stress. Even if some of the other factors listed above are also at play, fish are always made more vulnerable, and their symptoms are exacerbated by stress.

Stressed fish are known to have a lower reproductive drive and growth rate as well as a weakened immune system.

Pathogens that might otherwise not affect a healthy fish can be fatal to a fish that’s already crippled by stress, which is why it’s so important to keep stress factors to a minimum in the aquarium.

Can Hole In The Head Kill My Fish?

If hole in the head or lateral line erosion is left untreated, it may worsen to the point that your fish develops large bacterial infections that could kill them.

Another fatal scenario would be that HLLE erodes your fish’s lateral line sensory system so severely that they lose their sense of orientation and become gradually less and less interested in food and living, and they weaken and eventually die.

Thankfully, fatalities are easily avoidable from this disease if you follow the next set of steps for the prevention and treatment of this disease.

How To Prevent and Treat Hole In The Head Disease

The most important action you can take to treat hole in the head disease is to correct or eliminate whatever conditions are causing your fish to be stressed in the first place.

Therefore the first 5 Steps on our list are also the best preventative measures. Simply correcting the environment to the fish’s preferences alone is sometimes enough for your fish to make a full recovery.

Improve Your Aquarium Water Quality

Wolf Cichlid
Detail of an aquarium fish submerged in transparent water

Poor water quality is probably the number one underlying cause of hole in the head disease. A fish swimming in poorly maintained water is far more likely to be stressed, unhealthy, and at the mercy of parasitic and bacterial infections.

Test your water for dissolved oxygen, ammonia, and nitrate levels to help assess its cleanliness and overall quality.

Improve your water quality by performing regular tank vacuuming, partial water changes, and proper filter cleaning. Adding live plants is another way of regulating your tank’s water quality since aquatic plants are excellent at filtering out nitrates and toxins from the water and improving oxygenation.

Correct Your Water Chemistry

Even if your water is immaculately clean, you still need to make sure your aquarium water chemistry is set to the right parameters for your fish.

Oscars, for example, need a water pH of 6-8 and hardness of 5-20 dGH. If water parameters fall outside your fish’s preferred range, it can cause them stress and make them more prone to infections.

Ensure Correct, Stable Water Temperature

Hole in the head disease can sometimes be brought about by a single stressful event. If your aquarium’s water temperature is not stable, your fish may suffer from thermal shock which can lead to all kinds of health problems, including HLLE.

Always acclimatize new fish properly before introducing them to your tank and make sure you have a good heater with a reliable thermostat. Also, be sure to check the water temperature daily with a trusted aquarium thermometer.

Provide Your Fish With A Rich, Varied Diet

A fish’s diet is critical for a healthy immune system. Instead of just feeding the same old flake food to your fish every day, be sure to change their diet regularly.

With regular additions of frozen and live foods such as bloodworms, tubifex worms, daphnia, brine shrimp, mosquito larvae, and mysis shrimp, your fish will have access to far more essential vitamins, minerals, and proteins that will help them remain in prime condition, with robust immune systems.

Remove Bullies From The Aquarium

One of the main factors for stress in an aquarium can be the presence of incompatible tank mates. If you’ve noticed one of your fish being consistently intimidated or bullied by other tank members then it’s very likely to succumb to a stress-related disease at some point such as fin rot or HLLE.

Remove either your aggressive fish or the fish that’s being bullied and you may see a remarkable recovery from hole in the head symptoms within a short time.

Treat Your Fish With Antibiotics – The Last Resort

If you’ve tried all of the above strategies and still see no sign of improvement you may have to treat your fish with an antibiotic like metronidazole to eliminate the parasites and bacteria involved with the condition.

This should only be considered as a last resort rather than as a routine treatment because treating your tank with strong medications can drastically alter the ecology of your water, and wipe out the beneficial bacteria responsible for biological filtration and nitrification in your tank.

If possible, only use antibiotics in a hospital or quarantine tank so that your main tank is not affected.

Return Your Fish To A Healthy Environment

After your fish has been treated, it’s essential to return them back to the best conditions possible, observing all of the above points to prevent the condition from simply reasserting itself again. Keep a close eye on your fish and be sure to give them all the love and care you can muster.


Hole in the head disease is not only preventable but also treatable with good aquarium management and upkeep.

With scrupulous tank maintenance, correct feeding, and providing the ideal environment for your fish, you can reduce the chances of this disease ever becoming a serious problem in your tank.

Medications should only be used for HLLE as a last resort, and always in conjunction with the normal protocols for keeping your fish happy and healthy with strong immunity.

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