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. I differentiate between the two in that HITH involves parasites (Hexamita spp. and Spironucleus vortens) whereas HLLE do not. Even if lateral line erosion is not present I still classify those cases as HLLE. 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, 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.

HITH:

Many people do not believe any pathogens are involved with HITH or at least only secondary infections, not a sole cause of HITH. However, I have had a single case and heard of a number of other cases that show that metronidazole alone can cure a case of HITH.

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 you could not see the hole, 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 hole that had been under all that discharge. 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, still on a weekly 80% water change. The only change I have changed is that I no longer use a buffer to keep the pH at 6.5, and they were very recently moved to a planted tank (which holds at about 7.0). 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.

In tests it has been shown that Hexamita spp. and Spironucleus vortens were present in cases of HITH. These pathogens are susceptible to metronidazole. This further supports that HITH is caused by these pathogens.

I have heard of other cases where metronidazole was the only change and it cured the HITH. In even more cases it is part of the treatment, but obviously these do not necessarily support that parasites are involved.

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 of all the pathogen needs to be present. For example, if there is no Ichthyophthirius multifiliis in the tank then the fish will not get ick. 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 get started 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.). 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.

HLLE:

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

My 15” jaguar cichlid developed HLLE and I tried metronidazole to treat it but there was no effect. Many other cases have been attempted to be cured with metronidazole with absolutely no effect. This shows that there is more than just parasite induced HITH.

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 not 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 certain 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.

Different species seem to be more susceptible to HITH versus HLLE. Angels and discus seem to be more susceptible to HITH. 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 it 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.

We still do not know enough about HITH or HLLE. I am looking forward to it as we develop more knowledge about this and many other issues involved with fishkeeping. For now we simply need to do the best we can with the knowledge we do have. I hope this serves as a good explanation of the experiences of myself and all of those I have consulted.

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