Hole-in-the-head (HITH or Head and Lateral Line Erosion [HLLE]) syndrome is just that. It appears as holes and open pitted wounds around a fish’s head and along the lateral line, as if something is slowly eroding away the flesh. Many call this a disease but since it is caused by a great many environmental conditions and pathogens (i.e. a multifactorial etiology), so it is more properly called a syndrome.
In most cases the basic cause is lack of adequate filtration. Adding a lot of biofiltration is normally the best cure for hole in the head syndrome. Let me emphasize this:
Adding a lot of biofiltration is normally the best cure for hole in the head syndrome.
Some also treat fish with food laced with several medications. This medication is covered in this link:;
Note this topic is complicated and a very long and boring article is the result. So read on only if one is a nerd like the author.
Hole in the head Syndrome in Depth
Many separate hole-in-the-head and head-and-lateral-line-erosion into two separate syndromes. That just complicates thing. Both are diseases of neuromasts and both have exactly the same cause. Here is one Oscar with both syndromes:
How Hole-in the Head Forms
The head and the lateral line holes are where certain sensory cells called neuromasts are located. These sensitive cells are very prone to attack by high bacterial count and chemicals in the water.
There are several basic factors in hole in the head:
- Inadequate biofiltration such as a hang-on-back filter filtering an Oscar, give high bacterial water counts which cause hole-in-the-head.
- If the bacterial count in the water is high the neuromasts are easy points of attack by these bacteria
- If the water has high levels of an irritating chemical the neuromasts are more vulnerable.
- If an underlying disease is present the cichlid’s immune system is less able to fight off the attack on its neuromasts.
- If the fish is a cichlid from the very bacteria free black waters of South America the fish is less able to fight off neuromast attacks because of genetics. Oscars and discus are the two species most often attacked.
If a South American cichlid such as an Oscar or a discus is swimming in water with a high bacterial count, it will invariably get hole-in-the-head syndrome. What is confusing for some is that sometimes an Oscar or a discus can get hole-in-the-head in very well filtered crystal clear water. Contrary to popular mythology, hole-in-the-head is not ALWAYS the result of “poor husbandry”.
Note that bacteria count is a logarithmic scale. A fish will have problems at one billion bacteria but not be better till one million bacteria. So a 50% water change which drops the bacterial count from one billion to half a billion won’t help anything.
Causes of Hole-in-the-head Syndrome
This syndrome is very complex with lots of factors which contribute to it, what scientists call a “multifactorial aetiology”. Fish with HITH typically have two or more of the following problems:
- 80% are swimming in water with high bacteria counts
- 70% are being filtered with hang-on-back or sponge filters (i.e. inadequate biofiltration)
- 30% have mycobacteriosis (“fish TB”)
- 30% have hexamita (“internal parasites”)
- 20% have internal bacterial attack such as aeromonas
- 10% are starved
- 80% are South American cichlids
- 100% have “secondary” bacterial infections in the lesions
This is EIGHT separate but interrelated root causes of HITH.
Another way to look at these causes is to look at the interrelationships:
- High bacterial counts (i.e. “bad water quality”) are found in the water of most fish with HITH. High bacterial counts in the water both compromise the immune system of the fish AND directly attack the neuromasts
- Hang-on-back or sponge filters which have inadequate biofiltration capabilities will give “dull”, cloudy, bacteria filled water which contributes to hole-in-the head through several means.
- Necropsies done on fish that have died of HITH show the following conditions:
- Many HITH fish have fish TB (mycobacteriosis) in granulomas in their organs. TB compromises the immune system.
- Many HITH fish have hexamita (spironucleus) organisms in large numbers in the gut and sometimes in other organs in the body. Hexamita lowers the immune system.
- Hexamita is often associated with a lack of vegetable fiber or chitin in the diet
- Many HITH fish have organs infected with bacteria such aeromonas species. This lowers the immune system response.
- Some HITH fish appear to have been starved. Starvation lowers the immune system.
- Hole in the head is almost always found in South American cichlids with Oscars and discus probably being 60% to 70% of the cases.
Asking which of these conditions’ “causes” HITH is like asking which came first: the chicken or the egg. For instance, a hang-on-back filter is not removing the dissolved organic compounds rapidly enough, resulting in a high bacterial count in the water. The canal neuromasts on the head of an Oscar becomes eroded because they are being attacked by high bacteria in the water. High bacterial counts in the water also cause the immune system of the fish to be compromised.
The compromised immune system in turn causes disease like hexamita to flourish in the intestines and/or TB to develop. The invasion of the intestines and organs of the fish by hexamita and/or TB further compromises the immune system. The compromise of the immune system allows bacteria to attack the neuromasts even more. So, what is the actual cause? It’s just impossible to single out one cause.
The lesions for HITH are always loaded with bacteria when the lesions are cultured. The bacterial cultures always have a large variety of bacteria, which indicates secondary infections. But note that the term “secondary” does not mean that these bacteria are not doing a lot of damage and causing the ulcers to become much larger in size.
Treating Hole-in-the-head Syndrome
To treat HITH, one needs a multi-pronged attack:
- High bacterial counts are found in the water of most fish with HITH. High bacterial counts compromise the immune system of the fish. Add much more biofiltration (canister, under-gravel or sump) with a good media like foam, plastic pot scrubbers or static K1 media. Note that after enough brown gunk is accumulated on them, even very poor media like ceramic rings, Matrix, lava rock or bioballs oxidize ammonia. The reason these are poor media is that they do little or nothing to reduce the bacterial count in the water. It is this bacteria that can cause HITH.
This is the single most important thing to do if one has hole-in-the-head. It’s importance cannot be over-emphasized!
Remember the cardinal rule of filtration for healthy fish:
One Pound of Fish Needs 100 Square feet Of Biomedia Surface Area
This amount of biomedia give good water clarity and good fish health. Note that ammonia and nitrite oxidation only require 5 square feet of biomedia surface area. Many people come on social media saying “my fish are all slowly dying from something with no symptoms but I have zero ammonia and zero nitrite so my filtration is good. What gives?” “What gives” is that healthy fish need twenty times the surface area of biomedia than what is needed for ammonia oxidation. This fact is missed by all on social media.
- Hang-on-back or sponge filters which have inadequate biofiltration capabilities will give “dull”, cloudy, bacteria filled water which contributes to hole-in-the head through several means. Add much more biofiltration. Under-gravel filters do a great job of biofiltration if they are never cleaned. They do a very poor job of biofiltration if they are cleaned often. Sponge filters can give decent biofiltration if they have a powerhead added to the lift tube. And canisters are always much better than hang-on-back filters.
- Necropolises done on fish that have died of HITH show the following conditions:
- Many HITH fish have fish TB (mycobacteriosis) in granulomas in their organs. Treat by adding much more biofiltration and/or a UV sterilizer to the aquarium.
- Many HITH fish have hexamita (spironucleus) organisms in large numbers in the gut and sometimes in other organs in the body. Treat with metronidazole medication in the food and only in the food
- Hexamita is often associated with a lack of vegetable fiber in the diet Treat by adding fiber or chitin to the diet
- Many HITH fish have organs infected with bacteria like aeromonas. Treat with broad spectrum antibiotics in the food and only in the food.
- Some HITH fish appear to have been starved. Increase food amount.
The opinions on treating a fish with antibiotics or with metronidazole without clear cut evidence of the organisms being present, such as “white poop” or fin rot, is a matter of personal choice. Many experienced hobbyists, including myself, treat hole-in-the-head with with a “shotgun” food approach such as Ron’s medicated food or the food recommended in this link:
HITH Cases Seen on YouTube
Dr Richmond Loh is a well known aquatic veterinarian & fish pathologist. He wrote the excellent book “Fish Vetting Essentials” and has some very good videos on his YouTube Channel “The Fish Doctor“. He served as the 2014 President of the World Aquatic Veterinary Medical Association (WAVMA), and Secretary of the Aquatic Animal Health Chapter of the ANZCVS. Dr Loh is an Adjunct Senior Lecturer at Murdoch University, has a Masters in veterinary pathology, Memberships in Aquatic Animal Health and Pathobiology, is a Certified Aquatic Veterinarian and one of only 11 Distinguished Fellows of the WAVMA.
Dr. Loh had an interesting video where he treated four large albino Oscars with advanced cases of severe HITH disease. Three of the fish died and necropsies confirmed they were loaded with fish TB (notable there was NO HEXAMITA organisms present).
The fourth fish had its water conditions greatly improved with a lot more filtration. It healed up quite nicely. This is simple proof that it is largely the water quality vis-a-via bacterial count which causes hole-in-the-head. Now one could argue that the improvement in water quality helped the fish fight off the fish TB so the HITH resolved itself. Six of one, half a dozen of the other.
Dr Loh had another YouTube video where he treated a aquarium of small cichlids all with hole-in-the-head. He found the owner wasn’t feeding the fish enough and they were starving. Notable there was NO HEXAMITA organisms present. There was also no fish TB or other internal pathogens on necropsied fish. And the filtration was good on the aquarium. The fish healed up nicely when their food amount was increased.
So a recognized expert in the aquarium field has found that the “causes” of hole-in-the-head are many and that hexamita is often not even present in the fish.
Note it is possible to have fish with even advance hole-in-the-head heal up with a multi-pronged attack, as this photo shows:
I collect photos of sick fish off social media. I’ve collected 27 photos of fish with hole in the head syndrome. 21 of those photos are of Oscars. That is VERY telling. Oscars are very sensitive blackwater fish, not Central American cichlids like many think.
Many people house fish like Oscars in aquariums with far too little biofiltration with the wrong type of filter media. This results in Oscars getting hole-in-the-head disease very often. Hobbyists fail to appreciate that required biofiltration is not dependent on the length of a fish but rather dependent on volume and weight.
And this dependency is what is called a “cubed relationship”. A 12 inch fish like an Oscar is eight times heavier than a 6 inch fish like a zebra mbuna. Two twelve-inch Oscars will run about one and a half pounds and needs at least one cubic feet of foam, pot scrubbers or K1 biofiltration to be really healthy. I.e. two FX6 filters or a large sump. See this link for more on filter media selection:
One and one half pounds of fish (two twelve-inch Oscars) is the equivalent of fifty 5-inch mbuna in a 100-gallon aquarium and is very very heavy stocking.
Because Oscars are from blackwater rivers and are very large heavy fish they are especially prone to hole-in-the-head.
An Oscar needs a HUGE amount of filter volume with VERY GOOD filter media.
The topic is covered in more depth in these links:
Note that Oscars frequently get hole-in-the-head after their diet is changed. And whatever the new food is get blamed for the hole-in-the-head. A common refrain is “I started feeding krill and my Oscar got HITH, so obviously krill causes HITH”. It was not the krill that caused the hole in the head. It was the switching of the food.
Oscars typically (but not always) don’t like to have their food switched. They like the same food day in and day out. Oscars are drama queens, when you switch their food they often just grind up the new food and spit it out uneaten (you can almost see them mouthing the words “you changed my FOOD? You $%#@!**&%#, spit pheweehhhe, spit). This uneaten food feeds a bacteria explosion and the bacterial explosion creates hole in the head, often quite rapidly. But note some Oscars eat anything put in their tank, including your fingers.
Unknown chemical poisons can cause hole in the head and death very rapidly, sometimes in days. Contaminated sand such as Carib-Sea Sahara Sand and Carib-Sea Tahitian Moon Sand has killed several tanks this way.
One interesting known cause of HITH disease in marine fish is activated carbon. Some activated carbon apparently gives out some very irritating compounds. These compounds do cause HITH disease in saltwater fish and relatively rapidly (15 days!). (Effects of full-stream carbon filtration on the development of head and lateral line erosion syndrome (HLLES) in ocean surgeon, Stamper et al 2011, and studies done by the Toledo Zoo and Jay Hemdal, 2020). What is unclear is whether or not this will happen in fresh water.
Myths about Hole-in-the-head
This “multifactorial etiology” also leads to a lot of false conclusions where one thing is singled out as the sole cause. Humans as a species seem to be completely incapable of accepting that anything in this world can be caused by a lot of root causes all acting together.
For instance, the knowledgeable and accomplished aquarist Tony Griffitts singled out nitrate levels as the “cause” of hole in the head and even hypothesized a “cause and effect” for it. In truth this is simply speculation on Mr. Griffitts part. And his “cause and effect” wasn’t really thought through. He cited no studies and a search of the literature shows no support for nitrates causing or even being part of the cause of hole-in-the-head. To his credit, Mr. Griffitts did eliminate this from his website after this article came up on the web.
In actuality invariably when one starts doing lots of water changes for a fish with HITH one also does things like adding good filtration. These parallel actions improve the bacterial count in the water and improve the immune system of the fish and the HITH gets cured.
In the section on nitrate toxicity we site many studies on fish which show nitrates have very little effect on fish health. One study showed levels of 440 ppm nitrate to be relatively benign even for blackwater fish like the Oscar. So nitrates are not a cause of hole in the head. For the studies go to this link:
There are many who claim that dietary and vitamin deficiencies cause hole-in-the-head. They are simply wrong. No objective scientific links based on experimentation has been shown between diet and hole-in-the-head. These claims are simply marketing hype for vitamin laced foods.
Others claim the hexamita organisms directly causes hole-in-the-head and is the sole cause of HITH. This is based on faulty research by some graduate students who failed to recognize that they were conflating a hypothesis with an objective conclusion.
The fact that hole-in-the-head syndrome is not caused by hexamita has been known for a long time. The book “Handbook of Fish Diseases”, Dieter Untergasser, 1989, page 115 says:
“Up to now hole-in-the-head disease has been ascribed to the flagellates hexamita or spironucleus. Cichlids have often been found with hole-in-the-head disease with no flagellates in their intestines. The flagellates found in the holes were often of nonparasitic species normally inhabiting aquarium water. In many instances, after successfully controlling the flagellates found in the holes, no improvement occurred in the fish with the disease.”
See the section below on hexamita for more on that myth, including all the papers and references on how it originated.
Canal Neuromast Inflammation
In small cichlids hole-in-the-head syndrome is manifested by little white spots on the head. This is called “canal neuromast inflammation” and is relatively common. More information on this can be had at this link:
Aquarium Science Website
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