Head and lateral line erosion (HLLE) is a chronic condition in fish that stems from the lateral line, which is a linear sense organ running along both sides of most fish just below the surface of the skin, usually marked externally by a series of pores that open out through the scales.
Close inspection of affected fish may reveal small pits in the epidermis (skin) around the head and lateral line progressing to large, usually non-hemorrhagic (non-bleeding) ulcers. These lesions are frequently without pigmentation and may extend the length of the lateral line.
HLLE is a common syndrome of marine species kept in captivity. The clinical lesions of affected fish include superficial erosions of the head and face, which progress along the lateral flank to involve the lateral line. The clinical disease is usually non-fatal but can result in permanent scarring of the skin.
The primary cause of HLLE has not been discovered, although environmental stressors such as poor water quality, inadequate nutrition and the presence of opportunistic pathogens appear to be involved. Recent reports of a reovirus isolated from a very sick angelfish displaying the initial lesions associated with HLLE may support the theory of an immunocompromised state existing in fish affected with HLLE. Since aquatic reoviruses tend to have a low pathogenicity (disease-causing ability), they are generally found in association with stress-related disease outbreaks. Further studies will be necessary to establish an etiologic link between HLLE and the reovirus.
In most cases, the disease does not cause death. Affected fishes usually have been in captivity for several months or longer. Tangs (Acanthuridae) and marine angelfishes (Pomacanthidae) frequently display lesions consistent with HLLE.
Diagnosis of HLLE is based on the history and the appearance of the fish. Since this problem appears to be more of a syndrome than a specific disease, definitive "diagnosis" is difficult. Your veterinarian will be able to rule out bacterial disease, parasitic disease and trauma by examining your fish and taking harmless skin biopsies.
HLLE does not usually kill fish and affected individuals have been known to survive for years with only mild progression of clinical signs.
To correct this condition, a change in husbandry is nearly always required. Improving nutrition combined with removing external stressors (aggressive tankmates and poor lighting, for example) may arrest or even reverse the syndrome.
Treatment with antimicrobials (antibiotics) alone is unsuccessful, although, resolution of the lesions may be seen with vitamin C supplementation or elimination of activated charcoal from the filtration systems.
The best way to prevent this frustrating problem is to avoid keeping species that are susceptible to the syndrome. Your pet store clerk and a variety of text books and magazines can help with species selection.
If you do keep HLLE-vulnerable species, then you will want to provide them with optimal environmental conditions, including: a fresh, balanced diet, artificial sunlight, preferred water temperatures and crystal clean water with frequent water changes.