Hole-in-the-head disease, also known as Head and Lateral Line Erosion (HLLE), Lateral Line Erosion (LLE) and Lateral Line Disease (LLD), is a common disease for both freshwater and saltwater fishes. As the name states, this disease affects the lateral line organ and skin covering the head and face of the fish. Although there is no one cause for this disease, good basic husbandry practices and a low stress environment can severely decrease your fishes’ chance of showing clinical signs.
What Is Hole-In-The-Head Disease?
Hole-in-the-head disease is found in freshwater and saltwater fish and is named for the erosive lesions that form along the head and lateral line. There is no clear causative agent of hole-in-the-head disease. This disease mainly causes aesthetic issues and can cause an increase in secondary infectious, including bacteria and parasites. It may affect the head and/or lateral line and may be localized or spread out across the fish.
What Is the lateral line?
The lateral line is a specialized organ in fish that allows them to sense vibrations in the water around them. Made up of a series of connecting channels, just below the skin’s surface, this unique organ allows fish to school together, avoid obstructions in their path and sense when you approach the tank or pond. Fish have ears, like many other animals, without the external features, but the lateral line allows them a more comprehensive view of their underwater world. It is not related to the Ampullae of Lorenzini, commonly found in some species of sharks and rays, used to detect electrical currents underwater.
Symptoms of Hole-In-The-Head Disease
As the name states, hole-in-the-head disease causes pitting and erosions along the head and/or along the lateral line. The spots may be slightly depressed and brown to grey to white in coloration. Mild cases may only have a few spots, whereas serious infections may start to erode large patches of the face and sides. Erosions usually start as pinhole size defects and spread outwards. They can start as multiple spots at once or one focal lesion.
Causes of Hole-In-The-Head Disease
There is no singular cause for hole-in-the-head disease, and there are some species of fish that seem predisposed to it, such as Tangs and Surgeonfish. Although occasionally caused by a parasite (Hexamitid spp.), it is not commonly found with most infections. Many stressors, such as poor water quality or diet, can start the chain of events that lead to hole-in-the-head disease.
Other possible causes or influences on the progression of hole-in-the-head disease include:
- Stray voltage
- Stressors including aggression and poor water quality
- Nutritional deficiencies
- Use of activated carbon
How do fish get stressed?
Like us and our fluffy pets, fish process stress very similarly. The pathway of catecholamines, responsible for the “fight or flight” reflex, is very beneficial in the short term. But if it is constantly activated, such as with poor water quality or a territory dispute, a chronic stress situation unfolds, decreasing immune function, fecundity and growth. This is the main process behind poor water quality leading to many secondary illnesses, including Hole-In-The-Head Disease.
Treatment of Hole-In-The-Head Disease
Since there is no one cause of Hole-In-The-Head Disease, there is no one treatment. Your veterinarian will narrow down the potential influences and usually suggest a multi-step approach. They may recommend an anti-parasitic medication in addition to better maintenance practices and other methods to alleviate stress in your system. If aggressive fish play a role in your tank, such as fighting over territory or some fish stealing food out of the gills of other fish, you may need a long term solution including rehoming some fish. Remove all carbon from your system and make sure all of your filters are properly hooked up and not discharging extra voltage.
Depending on the severity of the lesions, your fish may or may not regain their original appearance. Although complete resolution is possible, your fish will likely have some mild color variation in healed patches of skin. Severe lesions may never fully heal.
How to Prevent Hole-In-The-Head Disease
Since the disease is multifactorial, you should keep many different influences in mind when keeping Hole-In-The-Head out of your system. Limit the spread of disease in your saltwater tank by following proper quarantine protocols for all new fish, adhering to a regular maintenance schedule and feeding your fish a healthy diet. Minimize stress by keeping suitable species together and making sure your tank is big enough. If any of your fish start to show clinical signs, they should be moved to a quarantine tank.