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HLLE and Activated Carbon: Looking for a Link
Chevron Tang with Head and Lateral Line Erosion starting behind its left eye.
Toledo Zoo to study possible role of activated carbon in onset of HLLE
Head and Lateral Line Erosion (HLLE) is a chronic, often progressive problem affecting captive fishes. Starting as small pits around the fish’s eyes, light-colored lesions develop bilaterally along the fish’s lateral line system, a sense organ that can be seen on many species as a line running down both sides of the animal.
Although rarely fatal, it causes disfigurement, making the fish less suitable for display. At least 13 families of fish have been identified as having developed HLLE in captivity. Not all species of fish show the same symptoms, and they do not always develop lesions to the same degree (Hemdal 2006). Many causes and cures have been suggested over the years, but controlled studies are lacking. The Toledo Zoo study will examine the use of activated carbon and how it coincides with the development of HLLE lesions.
A survey undertaken in 2009 of 100 advanced aquarists identified over 25 possible causes for HLLE in marine fishes. The majority believed that HLLE in marine fishes such as tangs and angelfish is caused by some dietary problem, notably vitamin C, or highly unsaturated fatty acid deficiencies. General stress caused by captivity was also cited as a major cause. Other survey responses included stray electrical current, the use of copper medications, lack of natural sunlight, the use of activated carbon, or the presence of a variety of chemical pollutants. Viral and bacterial infections have also been implicated in causing this syndrome (Varner 1991, Hemdal 1989).
Carbon As A Suspect
In the survey, 18 treatment methods were reported to have given complete remission of HLLE symptoms in captive fishes. Eighty-four percent of the cases of remission involved moving the fish to a new aquarium as one part of the treatment. This indicates that there are conditions in aquariums that can be changed in order to reduce the incidence of HLLE.
When the survey results were limited to public aquarists, 19% of the respondents found complete reversal of HLLE by removing carbon filtration. In addition, 75% of this sub-group implicated the use of carbon in the development of HLLE in at least some instances. Pilot studies undertaken at the Toledo Zoo also demonstrated that the use of activated carbon caused formation of HLLE lesions in fishes.
Because of this potential link between carbon usage and HLLE, a study is being undertaken by the Toledo Zoo (Ohio) titled “The Role of Activated Carbon in the formation of Acute Onset Head and Lateral Line Erosion in Acanthurids.”” This project will examine the role that the use of activated carbon may play in the development of HLLE lesions in fishes.
This project will attempt to induce HLLE in Ocean Surgeonfish, Acanthurus bahianus, right, by adding activated carbon (and its dust) to the water. An identical control system will house fish not exposed to carbon. If HLLE manifests in the fish exposed to carbon, histopathology samples will be taken to look for the presence of carbon dust in the lesions. Finally, any affected fish will be moved to a carbon-absent system and observed for any possible remission of the symptoms. Attempts will be made to control any other variables. The test systems will be identical with new tanks and equipment. The fish will be fed a pellet food shown in a previous study not to induce HLLE (Tilghman et al., 2003). Stray voltage will be controlled, and no copper medications will be used. The test fish will be collected by a professional supplier of public aquarium fish, and will not be exposed to carbon prior to their arrival.
Measuring Lesions with LED Lasers
Determining how to measure HLLE lesions was considered prior to the start of the study itself. A basic determination could be simply whether the fish develops lesions under certain conditions or it does not. However, knowing the magnitude of the lesions and how quickly they develop is also important. How does one measure an irregular, growing lesion on a fish in an aquarium? Handling live fish can be problematic; some fish are difficult to capture and restrain, and stress is one of the variables that needs to be controlled. The use of anesthetics may interfere with study results.
A previous study (Hemdal 2010) demonstrated the refinement of an in situ measuring technique for live fishes using inexpensive twin LED (Light Emitting Diode) lasers set apart and parallel to one another. Software analysis of a digital image of the subject allows for the calculation of the size of HLLE lesions without the need to remove the living specimens from their habitat.
If the hypothesis is eventually supported, additional studies will be needed to determine the types of carbon involved, and how the carbon forms lesions. If it turns out that the hypothesis is not supported, then at least one suspected cause of HLLE can be ruled out, and additional causes examined using the same systems. The study will begin immediately and conclude by the end of 2010.
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Credits: Chevron Tang, Ctenochaetus hawaiiensis, top, by the author. Ocean Surgeonfish, Acanthurus bahaianus, courtesy US Environmental Protection Agency, Biological Indicators of Watershed Health.
Hemdal, J.F. 2010. Refinement of a Technique for Remote Measurement of Captive Fishes Using Parallel Lasers. Drum and Croaker. Volume 41, 2010.
Hemdal, J.F. 2006. Advanced Marine Aquarium Techniques. 352pp. TFH publications, Neptune City, New Jersey
Hemdal, J.F. 2003. Head and Lateral Line Erosion. Aquarium Fish 15(4):28-35
Hemdal, J.F. 1989. A Reported Case of Head and Lateral Line Erosion (HLLE), Potentially Caused by a Bacterial Infection in a Marine Angelfish. Drum and Croaker. Volume 22, No.3
Tilghman, G.C., Francis-Floyd, R. and Klinger, R. 2003 Captive Nutritional Management of Herbivorous Reef Fish Using Surgeonfish (Acanthuridae) as a Model. In: Marine Ornamental Species: collection, culture, & conservation. Cato, J.C. and Brown, C.L. editors. Wiley-Blackwell Publishers.