No aquarist wants to see hole in the head (HITH), or head and lateral line erosion (HLLE) in his or her fish. We investigate the orgins of this difficult to treat ailment.
HITH and HLLE are basically the same thing; the first confined to the head region and more prevalent on freshwater fishes, the other starting at the head and moving down the sensory canals that run the flanks of marine fishes’ bodies.
As aquarium diseases go, it’s quite an enigma. We can recognise the symptoms, albeit in the latter stages of an outbreak, but defining the cause is much more of a challenge. Treatment is more difficult again.
There are pathogens associated with the condition, diplomonad species of Hexamita, Spironucleus and Octomitus, but whether these are causes or opportunists making the most out of a bad situation is unclear.
In post-mortem examinations, both have at some point been implicated as connected, but to simply blame the pathogen is to miss out a big part of the story.
An infected fish usually develops pale, eroding holes over the head which can then proceed to move either side of the body. These patches of degradation enlarge, making the fish look as if it is being eaten alive by some unseen bug.
At this stage the fish is in real trouble. Not only is its immune system being heavily taxed, but the open lesions provide an entry point for other pathogens that can cause systemic illnesses — much like the bacteria that can enter a human body through a decayed tooth and lead to heart issues.
Causes of HLLE have been long debated, although nobody can say with certainty what is the main trigger. Activated carbon, specifically the dust it produces, has been linked with outbreaks in marine fish such as tangs.
Fish seem to improve when taken from tanks with activated carbon and those unexposed to it have a lower likelihood of infection.
Other factors discussed include nutritional deficiencies, especially key vitamins and dietary iodine. Improvements in nutrition have been shown to benefit affected fish.
It seems water quality can equally play a role. Fish kept in aquariums with high nitrate (NO3) levels succumb to the illness more readily than those that don’t.
Even stray voltage has been accused of bringing about the disease, with tanks that carry electrical currents supposedly enhancing susceptibility.
Role of stress
We can say with some clarity that stress plays a significant role and at the first instance of the illness any adverse conditions must be rectified immediately.
Treatment is reported to be effective in some cases, but not in others. A range of anti-pathogenic medicines is available, although many aquarists will lean towards those that contain the active ingredient metronidazole.
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