Vision, hearing, equilibrium, and the lateral-line are the four basic sensory systems of fishes. The lateral-line system is thought of as having two different parts- the inner ear and the neuromast lateral-line. the sensory receptors of this system are called neuromast organs and are very similar to the organs found in their ear. Generrally speaking, there are two main types of lateral-line receptors: epidermal organs and canal organs. All fishes have at least one of these types of receptors.

In modern fishes, the later-line system extends down the flanks of the fish and out into the head region, often encircling the eyes. This system can be seen with the naked eye and appears as a single, unbroken line running down the side of the fish. Some speicies have a broken lateral-line.

The lateral-line system is extremely important to all fishes. As a result, fish can sense water direction and speed as well as low-frequency vibrationss, such as those made by wounded animals in the water.

Furthermore, fishes maintained in an aquarium probably use their lateral-line system to sense the location of the aquarium walls.

At times you will see fishes that have the appearance of holes in their heads or along the lateral-line system. These holes are the results of degeneration o fthe epicdermal organs within the lateral-line. There are three main causes of these holes: environmental, nutritional, and pathogenic.

both environmental and nutritional degeneration are known as head and lateral line erosion or (HLLE).

Diagnosis of this disorder is quite easy, as the fish look as though their heads are decaying. They will have lesions our areas around the nuchal hump (kok) or eyes that appear to be dissolving. In very serious cases, the fish may show degeneration along the lateral line down the sides of thier bodies.

HLLE caused by environmental conditions is common in aquariums that have not had regular maintenance, especially with larger fishes, is regular partial wather changes.

The nutritional requirements of fishes vary widely. Often, when a species or specimen that has been kept captive for some time does not receive the proper foods, it will show signs of HLLE. This is very common for flowerhorns where they are all fed the same mixture of meaty food. A constant feeding of foods high in animal proteins will also often result in HLLE even if the aquariums is well maintained. This is a good reason to have understanding of nutritional requirement for your flowerhorn and that variety is "Key" .

Sometimes flowerhorn may exhibit lesions in the head area that look infected. These lesions will appear red and swollen and may have stringy matter streaming from them. Such signs are the classic symptoms of Hole-In-The-Head desease (HITH) disease.

These disease is caused by flagellates within the genus Hexamita. Ironically thogh, Hexamita spp. are actually classified as intestinal flagellates.

So what is the cause of HITH? The only flagellate that is similar to Hexamita is Spironucleus and neither are actually considered to be the pathogen of this disease.

Great Post, One of my oscars suffered from this. Every LFS told me it was HITH but it wasnt I tried curring him out of it and it din't work, unfortunately i had to euthanize him. The deterriations on the side of it's head got so deep that he started to bleed from them. I dint get why he was the only one who had it everyone else was fine, so thank for the article it gave me some closure just now I dint know there was such a thing as (HLLE)

my dad loves oscar, he been through about 10 of them. out of the 10 i would think 7 of them got affected with this

Great information. I had Oscars that eventually died of HITH disease and exhibited signs of HLLE. I think it was probably the high protein diet of feeders that eventually did him in.