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Marine Fish Head and Lateral Line Erosion
Cause, Cure, and Prevention
By Tony Griffitts
Head and Lateral Line Erosion (HLLE) is a common condition seen in marine fish kept in public and home aquariums. Symptoms are pitting on the head and deterioration of skin and scales along the lateral line. The most common fish to show the condition are tangs (surgeon fish), butterfly fish, and marine angelfish, but I have also seen the condition in other fish including clownfish. This condition only happens in aquariums that have been set up for months or years. Through experience and changing environmental conditions I have been able to halt and reverse the condition.
Since having built and operated Aquaworld Aquarium for the last 5 years I have seen many cases of HLLE in many species of marine fish. At Aquaworld I sometimes have fish with HLLE brought to me by hobbyist that had their tank set up for years. I would take these fish knowing they had little chance of being sold, but I would try to provide the fish with the best care possible.
The first step was to quarantine fish for 3 weeks and then introduce them to one of my reef systems. Overtime (usually several months) the HLLE would completely reverse, and you could never tell that the fish ever had the condition. Through talking to customers with fish with the HLLE condition I have been able to correlate it to a common aquarium condition. The common factor in all cases of HLLE in marine fish I have seen is HIGH NITRATE.
While it could be some other environmental factor/s that actually causes the condition, I have never seen the condition in marine fish that were kept in well maintained reef aquariums with 50 ppm or less of nitrate. In all cases I have seen, the nitrate was always above 100 ppm. At exactly what concentration of nitrate the aquarium needs to be at before HLLE begins to appear is different depending on the species. Purple Tangs (Zebrasoma xanthurum) appear to be the best barometer for letting you know that your nitrate is too high, followed by Pacific Blue Tangs (Paracanthurus hepatus) and Sailfin Tangs (Zebrasoma veliferum).
In the past I have seen the condition pop up within just a week or two in some species of tangs (Sailfin/Zebrasoma veliferum, Pacific Blue/Paracanthurus hepatus, and Yellow/Zebrasoma flavescens) and butterfly fish (Heniochus acuminatus) in a fish only system where nitrates had been above 400 ppm. These fish were provided excellent diets, and the condition still developed. After performing a 75% water change on the system, dropping the nitrate down to less than 115 ppm, HLLE no longer develop in these species. Massive water changes from 50 to as near as 100% as possible will not only stop HLLE from getting worse, but will actually reverse the condition if the nitrate is maintained below 40 ppm.
This Purple Tang (Zebrasoma xanthurum) was completely cured and then sold. This Pacific Blue Tang (Paracanthurus hepatus) developed Head and Lateral Line Erosion within a week or two of being introduced to an aquarium with very high nitrate.
While nitrate is always present in high concentrations when HLLE develops, it may not be the actual cause, but rather a sign that the water quality has deteriorated beyond an acceptable level, and some other water parameter/s that accompanies high nitrate water is out of acceptable level/s. Without a controlled lab experiment where nitrate is purposely introduced to the tank and all other factors have been monitored and eliminated can I say nitrate is the definite cause, but it is where I would look first before I would look elsewhere.
In all cases of curing HLLE no special change was made to the diet of the fish. Providing the fish with water with low nitrates and/or doing large massive water changes to keep the nitrate low (below 40 ppm) always reversed the condition.
While it is possible to reverse HLLE, it is a slow process and can take months. The best practice is to prevent it from happening with proper maintenance. To prevent HLLE from developing, I suggest you first start with a proper aquarium set up. A Deep Sand Bed (DSB) consisting of fine aragonite (coral based sand) of 2 to 3 inches will help control nitrate accumulation by providing an environment for anaerobic bacteria to establish and break down nitrate. A DSB can also help maintain calcium and alkalinity levels. Using a refugium with macro algae as a filter will also help reduce nitrate, and in some systems it can help keep it near 0 ppm or undetectable.
A Deep Sand Bed (DSB) helps control how fast nitrate can accumulate in the aquarium. Whether you have a fish only or reef aquarium a DSB can prove to be very beneficial.
If your current aquarium eco-system produces a lot of nitrate every month, large percentage water changes to reduce the nitrate must be performed. How much will depend on how fast nitrate accumulates. Small percentage water changes of say 25% a month will only reduce the concentration of nitrate by 25% (provided the new water has no nitrate). If your goal is to maintain a nitrate level below 50 ppm, and your accumulation is 25 ppm every 4 weeks, then you will need to change 50% at a time. Biweekly water changes of 25% will not reduce the nitrate by 50% in the same four week period. In fact if you were to continue this practice your nitrate will continue to climb well above 50 ppm. After just 2 water changes your nitrate concentration would be around 47 ppm after completing the second water change. Large percentage water changes will not adversely affect the animals of the tank as long as the new water is well mixed and the salinity and temperature are close to the aquarium values. As a general practice I never do less than a 50% water change even on aquariums where the nitrate reads undetectable. When taking water out of the aquarium never gravel vacuum the sand bed. This will upset the ecological balance of the bed, removing beneficial organisms and destroying the anaerobic layer. If there is detritus accumulating on top of the sand bed, just pull it off the top. Adding a small power head that creates a little more water circulation in the tank will help keep the bottom free of detritus accumulation.
While HLLE appears to be related to high nitrate, and not nutrition or internal parasites or stray voltage, providing proper environment and nutrition for the type of fish you are trying to keep should not be ignored. If you want to enhance the food provided with vitamins, or garlic, you can do this, and in some cases it may shorten the recovery time, but at this time I have no experience to say it definitely will.
I hope this article clears up some written misconceptions about the cause of HLLE in marine fish, and provides you with a real solution to the condition. Don't forget to do those large water changes!