Head And Lateral Line Erosion

Posted by beth on 27 Feb, 2020

Head and Lateral Line Erosion-HLLE or Hole in the Head Disease is not a contagious fish disease but, rather, a condition where the epidermis and scales, primarily along the lateral line and face of the effected fish, become pitted and eroded. HLLE is thought to result in captive fish subjected to poor environment, poor nutrition, poor care and sometimes even another disease process. There is not always an obvious “cause” because many hobbyists may have what is considered a good setup with even  “pristine” water quality, but still have developing HLLE on a fish. If the cause of HLLE is not adequately addressed the smaller pits observed at the onset of the condition will enlarge and spread and could end up covering much of the fish’s body.  The fish will show eroding and frayed fins in addition to wasting flesh, and may ultimately develop serious disease processes such as bacterial infections.


There are several ways to address HLLE:

Grounding Probe

All marine tanks must have grounding probes installed in each system: the tank, the sump, the refugium, etc. The grounding probe must be installed along with a properly installed Ground Fault Circuit Interrupter (GFCI) where tank electrical equipment is plugged in. There is no “ifs or buts” about this. Grounding probes are necessary to prevent the electrocution of hobbyists.

But what does it do for fish and the prevention of HLLE?

Debatable is the answer.  The long-standing hobbyist theoryGrounding probes should be installed in all tanks and supporting systems [sumps, refugium] due to stray voltage in the aquaria caused by electrical equipment used in and near tank water [powerheads, lighting, heaters, filters, etc.]. Stray voltage is a causation of HLLE in sensitive fish such as tangs and angelfish; the irritating nature of this stray voltage results in the erosion of the lateral lines of fish. Properly installed [grounded] grounding probes in conjunction with a GFCI will divert or eliminate stray voltage out of the tank, thereby reducing or eliminating the cause of HLLE.

There is considerable anecdotal evidence to support this hobby theory.

The alternative-perspective…

Grounding probes complete the circuit for electricity to flow, therefore causes more of a hazard to marine animals.

Explanation:   Tank equipment is connected to a properly grounded GFCI with a grounding probe installed in the tank. A minute amount of voltage occurs due to tank water contact with an electrically defective pump, heater, etc. This small amount of voltage passes through the grounding probe and IS NOT detected by the GFCI because the voltage is very low. Because this voltage goes undetected by the accompanying GFCI,AND the grounding probe provides a grounded source of current, the tank is now charged with minute amounts of electricity that poses a thread to marine life. If a grounding probe was not installed, there would be no “current” by which electricity could travel, therefore, no threat to marine life.

Grounding Probe Essential for Hobbyist Safety

The grounding probe connected to a grounded GFCI will allow current to flow through the water providing the path of least resistant which is through the probe [and not human hands, or arms]. Bottom line, grounding probes are for human safety, not fish safety.

Human safety must always be a priority, therefore grounding probes must be installed in the aquaria. 

Nutritional Deficiencies

Hobbyists must research the nutritional needs of each fish that they wish to keep & ensure they can adequately meet that animal’s food needs in their aquaria. There is a lot that could be said here on the specific needs of surgeonfish [tangs] or angelfish—fish species that seem more prone to HLLE, however, that would be a whole other discussion. Take it as fact that, whether considering HLLE prevention or cure or just good fish health, the nutritional value of food that goes into each and every fish determines its health, happiness and longevity. The internet and fish hobby forums provide a wealth of free information on how to take care of fish. And all fish-keepers that take this hobby seriously, must develop a personal library of references, whether that be books, articles, online references, conference materials, etc.Also, the lack of specific nutritional elements/vitamins have been suggested as causing HLLE. Specifically Vitamin A, C & iodine. Supplements, such as Zoecon or Selcon, can be useful supplements in addressing HLLE, but are not substitutes for good and essential nutritional choices for your species of fish.

A few suggestions:

1. Plan to keep species of fish with similar nutritional needs.

2. If you are going to keep fish that require a specific environment that produces that fish’s food, then you must first create that food-rich producing environment. Mandarians and lawnmower blennies come to mind. These are fish that almost wholly depended upon their environment for food, not the hobbyist feeding them processed food.

Activated Carbon

There is plenty of anecdotal evidence suggesting that the use of activated carbon in filters is a causation of HLLE in fish, particularly tangs. It is purported that HLLE can result when carbon particles leech into the aquaria, or the leaching of organics filtered by carbon, or by the removal of essential water elements by the carbon’s mechanical filtration component. Whatever is the cause, animals prone to HLLE kept in aquaria that relies on natural filters, such as sandbeds, live rock, refugium systems, macroalgae or mangrove tanks and good water movement throughout the system, usually remain healthy and free of HLLE.

That is not to say that hobbyist should throw out their canister filters. Rather, if HLLE erosion is an issue in your system, or if you plan to keep fish prone to HLLE, then use carbon sparingly rather than constantly. Use it for a few hours occasional to polish the water, not a constant exposure. Natural filters, regardless of disease considerations, is always a healthy choice for captive marine animals.

Other Diseases and Medications

Fish suffering from disease may also be susceptible to HLLE. Viral and bacterial infections, internal parasites, malnutrition [including incorrect diet imposed by hobbyist], mal-absorption of nutrients [possibly due to exposure to copper or internal pathogens] and even immune dysfunction may cause HLLE.

Copper, commonly used and abused in the fish hobby, is thought to cause HLLE. Copper is an immuno-suppressant drug which could be the reason why some fish exposed to copper develop HLLE. There are alternatives for treating fish diseases these days, that, in most cases, preclude the necessity of using copper . Copper is a heavy metal and a toxin that could have many adverse effects on fish, not the least of which is liver dysfunction, HLLE and immunological disorders.

Environment and Stress

Stress, though not a “disease”, is thought to be a factor in HLLE. Chronic stress, where the fish never enjoys a calm, peaceful wholesome environment, can result in HLLE. A tang placed in a 30 gal tank with minimal nitrates can be enough to cause the fish to develop HLLE. Several species of angelfish placed in a 120 gal fish-only tangs can be stressful enough to cause HLLE.

Poor water quality, poor nutrition, inappropriate diet, disease, inadequate environment for the species, too many fish, inappropriate use of medications, untreated diseases—-all can result in stress and immune dysfunction that could cause HLLE.

Poor water quality is thought to be a major cause of HLLE. Tanks with nitrates have an incomplete nitrogen cycle. This means that the nutrients in the tank caused by animal waste and excess food exceeds your system’s ability to export this waste. Of the many things believed to cause HLLE, water quality [nitrates] certainly ranks high as a causation, particularly with certain species of fish—tangs and angelfish.

The information offered here is a starting point in understanding HLLE, There are many good sources on the web for additional study. Hobbyists experiencing this problem should investigate further as there is no simple or single way to address HLLE. The condition can be reversed with diligence by assessing and addressing your fish’s individual needs.

Salfin Tang with HLLE and after successfully addressing the cause of the problem: