Hole in the Head (HITH) and Head and Lateral Line Erosion (HLLE) in Aquarium Fish

Hole in the Head (HITH) and Head and Lateral Line Erosion (HLLE) in freshwater fish are two complex issues with a lot of debate over the causes and cures for each. The fact that this issue is named after a symptom and not a pathogen should be the first clue that as a whole we are on the wrong track in thinking that they are the same issue. Another clue is the amount of debate and conflicting information and experiences should also clearly indicate that these are really two different issues. In more detail, the symptoms of each are not exactly the same, although they are similar and simply described as ‘holes in the head and lateral line’. But in closer detail the deep, narrow pits of HITH that frequently have a white discharge are actually very different than the wide, shallow pits typical of HLLE. This should all clearly indicate that HITH and HLLE are not the same thing.

An Oscar with Head and Lateral Line Erosion – HLLE:

how to treat hole in the head hith oscar

A Discus with Hole in the Head – HITH:

how to treat discus with hole in the head hith

Here is a discus with so much white discharge from hole in the head that you can’t even see the holes:

discus with hole in the head hith

I differentiate between the two in that HITH involves parasites (Hexamita spp. and Spironucleus vortens) whereas HLLE does not. Even if lateral line erosion is not present I still classify those cases as HLLE. The factual evidence supports the idea that HITH is caused by parasites, Hexamita spp. and Spironucleus vortens, while HLLE is not caused by any known pathogen, but is a condition with multiple causes, some more common than others.

I really started to take a close look into these conditions when my 15” jaguar cichlid came down with HLLE. As I researched I came upon a lot of resources and it seemed like every one of them thought they were an, or rather THE, expert and that the others were all wrong, and every opinion was different. So I went through as much information on the subject as I could find, talked to as many people about it as I could, and checked all the books I have or came across in bookstores. I did my best to absorb it all, comparing them all as I gathered more information. I tried to find the inconsistencies and the trends that seemed to be true of all the experiences.

A lot of strong trends developed. Many of the theories were supported by numerous cases. However, not all of these cases agreed with each other. The cases discussed are from people and cases online, cases from books, or people I have spoken to unless they are described as my personal experience. I have been careful to avoid taking what has been shown to be causes in marine HLLE and applying those to freshwater because you simply cannot assume it is the same thing at all. This article is specific to freshwater fish. From what I have read about marine HLLE it is well supported to be caused by poor nutrition.

Hole in the Head (HITH):

Many people do not believe any pathogens are involved with HITH or at least that they are only secondary infections, not the actual cause of HITH. However, I have had a couple cases and heard of a number of other cases that show that metronidazole alone can cure a case of HITH demonstrating that it is caused by parasites.

Hexamita spp. has been shown to be present in diseased ornamental cichlids (Francis-Floyd). Spironucleus vortens has been shown to be present in diseased angelfish (Poynton, 1995). The use of metronidazole as a medication added to the water, food, or used as a bath is an effective treatment against both Hexamita spp. and Spironucleus vortens. (Klinger). Both of these facts are well supported by the many aquarists who have used metronidazole to successfully treat HITH in discus and angelfish.

One idea is that Hexamita spp. is found in the digestive tract, so by treating with metronidazole the aquarist is actually treating a cause of malnutrition (the parasites are consuming too many nutrients and starving the fish) and that the malnutrition is the actual cause of the HITH. This is not supported by the facts. One study found that both Hexamita spp. and Spironucleus vortens can be found throughout the entire body of fish including the heart, liver, kidney, spleen, eyes, brain, and blood (Paull, 2001). This shows that both parasites can be found outside of the digestive system and act directly on the fish. Spironucleus vortens has been shown to be in the head lesions of infected individuals of discus and angelfish collected from the aquarium hobby that were showing moderate to severe lesions (Paull, 2001).

My personal case involves discus. Not long after I got my school of discus a couple of them came down with HITH. They had narrow, deep pits with white discharge. One actually had so much discharge that you could not see the holes at all, just the white discharge. They were in a 55 and I moved them into a 20 high. The diet was not changed, they were kept on just New Life Spectrum Thera+A. The water changes stayed the same (about 80% every week). The only difference was that I treated them with Aquarium Solutions’ Metro+, a metronidazole medication. Within a few days I saw improvement. The holes were getting smaller and the discharge was being reduced. At about this time you could see the holes that had been under all that discharge on the worst fish. Within a week the HITH was just about gone, with just a little healing left to finish. Now there is no scarring or any marks showing what had happened. In addition, after they were cured things were not changed. They are still on New Life Spectrum and still on a weekly 80% water change. If the diet and water quality is the same before and after the HITH but HITH has not occurred since the first time, then obviously the diet and water quality are not to blame in this case. What changed was the use of metronidazole, which wiped out whatever pathogen was causing the HITH (Hexamita spp. or Spironucleus vortens). If this was not the case then HITH would have almost certainly occurred again.

There are other cases where metronidazole was the only change and it cured the HITH. In even more cases it is part of a successful treatment.

Some theorize that small parasites make their way into capillaries causing these capillaries to be blocked, leading to the tissues past the blockage to become either necrotic or simply less supported by the bloodstream, leading to the deterioration of that tissue. Since nerves require a rich blood supply there are more capillaries around nerve dense areas, such as the lateral lines and sensors on the head. This nerve tissue may also be more sensitive to the effects of such blockages, causing them to be the first place to display the symptoms.

It is also theorized that poor water quality and/or diet stress the fish and allow these parasites (already present in the gut, but in a more subdued condition) to take hold. As they take a stronger hold they could be taking more of what nutrients the fish is getting, amplifying the stress of a poor diet. Then other issues discussed later in the HLLE section come into effect.

In my experience there are two requirements for illness in fish. First is that a pathogen needs to be present. For example, if there is no Ichthyophthirius multifiliis in the tank then the fish will not get ich. Secondly, the fish need to be stressed. This can come in MANY forms. Temperature, pH, other water parameters, water quality, aggressive tank mates, poor diet, and many other things can all cause stress in fish. This stress weakens the immune system and allows whatever pathogens are present a chance to flourish in the fish. In many cases removing these stressors can help strengthen the fish’s immune system enough that it can fight off the pathogen by itself, without the assistance of chemicals, medications, or other treatments (temperature, salt, etc.). Very few pathogens can infect fish without the fish being stressed, and these pathogens are rare in the hobby. Because of this I do believe that some cases that do not require metronidazole to be cured may actually have involved parasites, but by treating the initial causes of stress the fish was able to recover enough to fight them off on their own.

Head and Lateral Line Erosion (HLLE):

HLLE (cases not involving parasites as a cause) seems to be much more complicated with numerous causes. Because of this it seems that like Dropsy, HLLE is a syndrome or condition that can be caused by a number of factors, not a single distinct disease.

Water quality has been shown to be one of if not the most significant stressor in fish. In many cases of HLLE all that is needed is an improvement in water quality. In other cases an improvement in water quality and diet together prove to be all that is needed to cure HLLE. I have not seen anything describing the specific way in which low water quality (usually in the form of high nitrates and other harmful chemicals) actually causes the pits to develop. It may be that they stress the fish and/or its organ systems and physiology and this can end up causing physiological dysfunctions that could result in sensitive tissues (such as nerve tissues and their surrounding and supporting tissue) being affected first, then spreading to other tissues. This would reflect the progression of HLLE as starting out at the Lateral line and/or facial sensors then spreading to surrounding tissues, sometimes resulting in more hole than head and a severely eroded lateral line system.

Diet has also been shown to be a major issue with fish and HLLE. An incomplete diet can obviously cause an array of issues. Developments in human nutrition show how even very minor nutrients (nutrients being all macronutrients, micronutrients, and trace elements) can have drastic and detrimental consequences. There is no reason to believe this is not also the case with fish. Even if we do not understand exactly what all is vital or at least why, we know we must provide the best diet we can. Since an improvement in diet alone or along with water quality has been shown to cure HLLE, diet can cause HLLE. When diet causes HLLE it probably does so similar to the way water quality does. A deficiency in certain nutrients (maybe in general, maybe specific nutrients, maybe in certain combinations) could lead to stress on the fish and/or its organ systems and physiology, and/or physiological dysfunctions. As with water quality these could end up causing more significant physiological problems that could lead to the deterioration of sensitive tissues and then begin to spread.

There have been a number of cases where the simple presence of carbon in the filtration has actually caused HLLE. In these cases carbon was present when the HLLE developed. Either initially or after trying other treatments that failed or had little progress, the carbon was removed. At this point the HLLE went away. Once it was gone either the carbon was returned and the keeper was trying to get back to normal, or it was returned to see if it really was the cause. When the carbon was returned, so did the HLLE. This seems to be due to carbon removing vital trace elements and micronutrients. These have important functions in the physiology of the fish and its organ systems. This may be similar to how diet can cause HLLE, a lack of vital nutrients causing physiological dysfunctions. These can cause stresses to the immune and other systems ending up being symptomatic in the fish as HLLE.

There is an idea in both fresh and saltwater forms of HLLE that it is caused by carbon dust. This does not make sense to me at all. Every single time I have seen this idea regurgitated it is simply stated with absolutely no factual support for this idea. In addition, I do not think anyone in this hobby uses carbon without rinsing it first, at least not more than once. This idea seems poorly supported, unfounded, and simply regurgitated over and over. As a hobby we need to pay attention to ideas that have factual support, not guesses.

Different species seem to be more susceptible to HITH versus HLLE. Angels and discus seem to be more susceptible to HITH. I haven’t seen a single case in discus or angelfish that looked like HLLE. Other cichlids seem to be more susceptible to HLLE. Some species seem to be susceptible to both. I have seen both in Oscars.

From what I have seen many if not most people want to hear ‘X causes HITH/HLLE’. This would mean if you fix X then the HITH/HLLE will be cured and go away. The evidence simply shows that there is not a single cause. At best the answer seems to be ‘X, Y, Z, and W can cause HITH/HLLE’. There are simply too many cases that show one thing while another case shows another. Many people seem to block out or deny valid information because it does not agree with their current opinion. This is a science and all the information needs to be considered, not just what agrees with your current opinion. Which of these issues is/are in effect in any given case needs to be dealt with on a case-by-case basis. Many people seem to take their own experience and apply it as the rule to the experience of others. We need to realize that a larger sample size (the experiences of everyone we can talk to about it) is more accurate than our own experiences, no matter how vast they may be.

The biggest problem is when people are speaking from experience with different species. If HLLE in an oscar is being discussed and someone with experience with HITH in discus chimes in, it simply won’t mesh. It is just as irrelevant as discussing ich when others are discussing HLLE.

Many people want scientific evidence before they will believe anything. This is good in general, but unfortunately very little research is done on aquarium fish. Most related studies are done on more economically significant species that are used for food. We are lucky to get the occasional study that can even be used in any way. However, if we use the experiences of aquarists we can tap in to a resource that makes up the second most popular hobby in the United Stated (Riehl, 1996).


Francis-Floyd, Ruth and Reed, Peggy, Management of Hexamita in Ornamental Cichlids. University of Florida IFAS Extension, VM67

Poynton, S. L., Fraser, W., Francis-Floyd, R., Rutledge, P., Reed, P. and Nerad, T. A. (1995), Spironucleus vortens N. Sp. from the Freshwater Angelfish Pterophyllum scalare: Morphology and Culture. Journal of Eukaryotic Microbiology, 42: 731–742. doi: 10.1111/j.1550-7408.1995.tb01625.x

Klinger, RuthEllen and Francis-Floyd, Ruth, Introduction to Freshwater Fish Parasites, University of Florida IFAS Extension, CIR716

Paull, Gregory C. and Matthews, R.A., Spironucleis vortens, a Possible Cause of Hole-In-The-Head Disease in Cichlids, Diseases of Aquatic Organisms, 45 197-202, 2001

Riehl, Rüdiger. Editor.; Baensch, HA (1996. 5th Edn.). Aquarium Atlas. Germany: Tetra Press