There are many "theories" as to why this disease occurs, but there seems to be
no single definitive answer that can be pinpointed or solely connected to it. Many of the contributing theories include stray voltage in the aquarium, poor water quality and environmental conditions, high nitrate levels, lack of vitamins and poor nutrition, stress, parasitic infestation (a protozoan,
Octomita necatrix), using carbon, and that some fish may just be genetically pre-disposed to this disease condition.
This disease stems from the lateral line that fish have, thus appropriately named Head and Lateral Line Erosion (HLLE). It is also referred to as Lateral Line Erosion (LLE),
Lateral Line Disease (LLD) and Hole-In-The-Head Disease. It
appears as open pitted wounds around a fishes head and along the lateral line, as if something is slowly eroding away the flesh. HLLE disease in the short run is not fatal, but over the long run if the disease continues to progress the fish stops eating and becomes lethargic. The open wounds make the fish susceptible to other infections which in turn leads to the further deterioration of its health, and these secondary infections are what may eventually lead to its demise.
