HITH; Hole in the Head Disease in Fish

I have had a lot of questions directed either to me or through the forums that I am active in about Hole in the Head Syndrome, often simply identified as HITH.
I will start off with by saying that I do NOT know everything there is to know about this disorder only to say that I have had a lot of experience in treating and ridding fish afflicted with this problem in my maintenance business over the years. I will also note that I NEVER had an outbreak in the last 20 years of my business due to proper care of fish prone to this disorder. I state this because there is a lot of anecdotal information about HITH or even simply half truths.

What is Hole in the Head Disease?

HITH is an affliction that primarily affects Gouramis, Angelfish, Discus, Oscars and other South American cichlids.
A Cichlid has spots on their head which are called sensory pits. These are a series of fluid filled sacs with tiny hairs that sense vibrations and convert them to electrical impulses. Along the lateral lines, sensory pits are responsible for a fish's equilibrium in the water and look like little pin holes, generally arranged in a cluster.
In a HITH outbreak these sensory pits become eroded with ulcerated lesions which expand and coalesce together, forming larger crater-type lesions. They can extend deeper into the muscle and even down to the skull. These open lesions may become secondarily infected with bacteria or fungi and such secondary bacterial infections that may result in death.
A common theory is that HITH is caused by non-absorption of minerals and vitamins from the intestine due to heavy concentrations of flagellate parasites, like Hexamita. It is sometimes believed by aquarists that the protozoan parasite Hexamita caused the skin erosions and therefore treatment is based on attempting to eradicate Hexamita by treatment with Metronidazole. This is where a half truth does come into play; Often there is a misunderstanding as stated above as to the root causes however there is also a misunderstanding of what Metronidazole is effective against. I this article I will not go into detail about Metronidazole other to say that it IS effective against many bacterium, especially intestinally which can effect absorption of important minerals and vitamins, WHICH IS WHY Metronidazole has been effective even when the cause was misidentified. The bottom line is Metronidazole is both antibacterial AND antiprotozoal.
Please read more about Metronidazole in this article:
“How Aquarium Medications Work; antibiotics

Treatment/Prevention

This is also an area where many half truths are present (and quite honestly much is to be learned as well).
Obviously diet plays a role here, as well as water quality such as Nitrate levels, however what is sometimes missed is the role Calcium plays in proper osmoregulation and the fish’ ability to absorb other nutrients. Often poorly maintained aquariums will see high amounts of acids, poor Redox reduction, high DOC (dissolved organic compounds), and low GH and KH. I have also noted in my service calls that the aquarist (usually with South American fish) was told to keep a low GH; nothing could be further from the truth!
I would recommend reading this article for further information about the importance of proper Calcium levels in ALL aquariums:
“The Importance of Calcium, GH, KH and Electrolytes in Aquariums”

Here are some steps to take for cure and prevention of HITH:
• Make regular, frequent but small water changes such as 20-30% per week or even twice per week, The use of a gravel vacuum ensures better removal of decomposing wastes that add acids to the water and lower other water quality parameters such as Redox.
• Lower nitrates, this is important IMO and nitrate levels should be lower than 40 ppm or better, lower than 20 ppm.
Please read this article about the nitrogen cycle for more nitrate information:
"Aquarium (& Pond)Nitogen Cycle"
• Vary diet, gut load feeders with foods such as Spirulina 20 or similar high vitamin and mineral foods. Feed high quality pellets as well (or flakes if the fish will eat them). However since Freshwater fish do NOT drink the water around them liquid vitamins are less effective, but I would still give them a try as well in severe cases especially.
Please read this article about fish nutrition for more about “gut loading”:
"Fish Nutrition (Proper Aquatic Nutrition). What ingredients are needed for optimum fish nutrition, growth and health"
• Increase GH to at least 100 ppm (better is 200 ppm), Wonder Shells along with water changes help here. Also make sure your carbonate hardness (KH) is at least 50 ppm (over 100 is often better)
• In moderate to severe cases treatment with Metronidazole may also be necessary as well as other antibiotics such as Nitrofurazone (Furan Two)

Above a clean WELL filtered aquarium is a MUST.