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Cause of HLLE (Head & Lateral Line Erosion) in Saltwater Aquarium Fish

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A breakthrough study solves one mystery of Head and Lateral Line Erosion (HLLE). The following information was reported in the Coral Reef and Marine Aquarium Newsletter.

Head and Lateral Line Erosion (HLLE) is a type of skin erosion that affects some species of marine fishes in captivity.

To begin with, HLLE normally appears first as small pale pits around the fish’s eyes. These may develop into light colored lesions along the fish’s lateral line area, then spreads onto wider areas of the body. Fish that develop severe lesions are usually permanently scarred.

HLLE is not normally seen on fish in the wild. It seems to appear only on fish which are in captivity. HLLE is most often seen on fish in the surgenfish family, but has been noted on up to 20 other fish families.

Up until recently, the cause of HLLE has not been fully studied, but Jay F. Hemdal, the Curator of Fishes and Invertebrates at theToledo Zoological Society has changed that. He has just completed a very interesting study of the cause of HLLE, which was funded by the Toledo Zoo. The study involved three 120 gallon marine aquarium systems (two tanks per system) which were established using typical home aquarium equipment and synthetic seawater. Live rock was utilized as the basis for biological filtration in all three systems. Thirty-five Ocean Surgeonfish, (Acanthurus bahianus) were evenly distributed among the three systems at the start of the study.

A week after the fish were introduced to the tanks, 500 grams of unwashed lignite carbon was placed in a mesh bag and added to the filter sump of the first system. At the same time, 500 g of extruded pellet carbon was placed in a mesh bag and added to the filter sump of the second system. No carbon was added to the control (third) system.

Minor HLLE lesions were noted on two fish 20 days after surgeonfish-with-HLLE-dusty-carbon-fed-NLS-8-29-2010the lignite carbon was added to the sump of their system. The lesions began to develop on the additional fish in that system, and grew in size until after four months, all of the fish in that system showed severe lesions (eventually involving over one third of their body surface).

The 12 fish exposed to pelleted carbon did not develop visible symptoms, but microscopic lesions were discovered upon histological examination by an outside laboratory, and two of the fish developed minor lesions a few months after the conclusion of the study.

The 11 control fish did not develop any visible or microscopic lesions. Six months after the study was concluded, and the carbon was removed, the HLLE lesions remain on all originally affected fish, and the control fish are all still symptom-free.

The effect of lignite carbon on the fish was swift and involved all of the exposed fish. None of the control fish developed any lesions. Statistically, the results were definitive that lignite carbon use caused HLLE in these fish.

Lignite is a form of coal, sometimes referred to as brown coal. It is the lowest grade of coal, with characteristics that put it somewhere between coal and peat.

Read the full report of Activated Carbon: HLLE Smoking Gun Found

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