Activated carbon affirmed as causative agent for HLLE disease
Earlier this year, Jay Hemdal (et al.) conducted a ground-breaking study that was the first to scientifically establish a link between the use of granular activated carbon and Head and Lateral Line Erosion Syndrome (HLLES). The study is published in the North American Journal of Aquaculture.
Now a new study published in Journal of Aquatic Health has affirmed Hamdel's findings: Carbon does indeed cause HLLE. Researchers once again chose to work with Acanthurus bahianus, distributing seventy-two specimens between control and GAC-treated systems (this time using extruded coconut shell activated carbon). In the treated systems, HLLES developed exponentially over 15 days, progressing from the tangs' chins, then cheeks, then expanding and coalescing outwards. Once the GAC was discontinued, the HLLES reversed in a mean time of 49 days, regressing in opposite linear fashion as the progression.
Furthermore, Jay Hemdal provided Advanced Aquarist some anecdotal information from a researcher who found carbon dust in the lateral line of some fish suffering from HLLES using electron microscopy. The researcher emailed Hamdel: "The theory was small sharp <carbon> dust particles would get into lateral line and bounce around because of the hair cells causing the erosions and subsequent fibrosis."
For many decades, aquarists (including myself) have observed this phenomenon in aquariums. Yet, seemingly just as many continue to doubt GAC's culpability in HLLE. Two scientific studies have now come to the same conclusion. The independent findings solidify the link between activated carbon and HLLE. It is still unclear why HLLE does not develop in some aquarists' systems with GAC usage. More research is needed to understand all the criteria involved. This may, in time, lead to "anti-HLLES" GAC implementations and technologies. Perhaps all that may be required is using fine micron filters post GAC.