Head and Lateral Line Erosion - by Scott W. Michael Photos by Amanda Dellow
The lateral line is made up of organs located on the head (head-canal-system) and along the trunk (trunk-canal system). Some fishes (like gobies) lack lateral line organs, but most are well equipped with sensory pores and papillae on their heads. The lateral line organ consists of neuromasts located on the body surface (fee neuromasts) or in shallow pits, grooves, or canal (most reef bony fishes have the latter arrangement).
The neuromast is made up of a cupula, a long jelly-filled projection that ensheathes sensory hairs. These hairs are embedded in a sensory cell under the epidermis and are stimulated when the cupula is bent. Although the neuromasts continuously send nerve impulses to the brain, the frequency of impulses increases when the cupula is flexed in one direction and decreases when it is bent the opposite way.
This organ provides a sense of "distant touch." Because water is a noncompressible medium, molecules move when it is displaced or disturbed. The lateral line organ detects these movements, allowing a fish to gauge approximately how fast an object is approaching and how far away it is.
That brings us to the malady head and lateral line erosion (HLLE), which is also known as "hole-in-the head disease." This is a very unattractive condition that is common in certain groups of fishes. Although this is usually not immediately fatal to the fish, it can turn a radiant individual into a real eye sore! In a highly advanced stage, the ailing fish may become weak and have a suppressed appetite. Some groups of fishes that seem to be especially susceptible to this condition are the angelfishes, surgeonfish?€™s and Moorish idols. However, I have seen species representing numerous families suffering from this malady, including groupers, comets, dottybacks, grunts, butterflyfishes, damselfishes and wrasses.
Lateral line erosion usually begins to manifest itself after the fish has been in the home aquarium for several weeks to several months - this seems is in part a function of the fish species. In most cases, the first sign of the condition are light blotches on the head, namely around the eyes and nostrils. The skin around the pores of trunk-canal system then begins to erode exposing pigment free flesh. In more advanced cases, all the pigment on the face may deteriorate and the fins and even the gill covers may also begin to deteriorate.
So what causes this common malady? Some authors have suggested that HLLE is caused by a parasite in the genus Spironucleus - a close relative of the freshwater dinoflagellate, Hexamita that is thought to cause this condition in freshwater fishes (Bassler, 1996). It is thought that this parasite infects the digestive tract, causing stress and the associated loss of tissue around the lateral line organ. Bassler suggests using Metronidazole and antibiotics to treat the problem. However, in other studies, where fishes with advanced HLLE were examined (externally and internally) significant numbers of parasites were not found and this cause was ruled out (e.g., Blasiola 1989).
Another possible cause of HLLE is inadequate nutrition. Blasiola (1989) reported that Pacific blue tangs (Paracanthurus hepatus) with advanced HLLE that were given flake food supplemented with Vitamin C showed signs of improvement. Also, other aquarists have reported that Vitamin C supplementation did prevent or reverse this condition. Collins (1995) states that in his experience it is a lack of Vitamin A, not Vitamin C that is a primary cause of this condition. He reports having successfully reversed HLLE by increasing the amount of Vitamin A in the diets of surgeonfish?€™s. In his report, the water quality of the aquarium where the ailing fish were kept was good, they did not use carbon on the tank and they fed their fish a varied diet that included lots of Vitamin C, but still their Atlantic blue tangs (Acanthurus coeruleus) suffered from HLLE.
They began adding more Vitamin A to the diet, in the form of fresh broccoli, and the tangs were free of HLLE in six to eight weeks. He found that surgeonfish of varying sizes readily ate the flowerets of the broccoli, while only the larger acanthurids would feed on the woodier stalk. They also added fresh peas and shredded carrots to the diet (that latter is messier to feed then broccoli).
It has also been reported that the removal of valuable trace minerals by, or the leaching of harmful products from, activated carbon may incite the condition (T.
Frakes personal communication, 1992). Recently, I had the good fortune of being able to spend sometime with one of my favorite "fish guys," Jay Hemdal. We were talking with Omaha Henry Doorly Zoo aquarist, Mitch Carl, about a chronic problem they have been having in their largest display aquarium. Although sharks and rays do well in this enclosure, all the bony fishes suffer from advanced HLLE. Jay speculated that carbon dust might be a culprit in cases of this malady he had observed in the past. Mitch shared that they did have a problem with carbon dust, which was accidentally purged into the tank several years ago. After that, the HLLE had become a chronic problem. A chemist, John Austin, who was also involved in our conversation, suggested that the carbon powder would act as an irritant to the fishes integument, causing irritation within the neuromast pores (where the carbon dust may actually accumulate). This could result in the skin sloughing off along the head and trunk canal system.
Although more study is required to see if carbon dust is responsible for advanced cases of HLLE, I have seen and heard of other instances where fishes were suffering from HLLE in aquariums where carbon was constantly employed.
In one pet store I visited, almost all the fishes kept in the tanks were suffering from HLLE! Upon removing the carbon, the fish recovered. When employing carbon in your filters, you should be sure to rinse off as much of the dust as possible. Also, change it regularly so it does not break down and end up in your tank. It may be that other irritants, like silica, could cause HLLE as well. More research is necessary to confirm this.
Researcher, Dr. Robert Hildreth, reported that by employing an EcoSystem Aquarium filter with Miracle Mud® substrate he was able to stop and even reverse HLLE in two surgeonfish species (see
www.ecosystemaquarium.com). These surgeonfish?€™s were healed in four to six weeks after being placed in a tank with this type of filter. In his article, Dr. Hildreth makes no claims as to how this filter prevents HLLE. But he once told me it may have to do with the increased presence of trace minerals and elements, like iodine, in aquariums that use the Miracle Mud® filtrant. A lack of iodine in the diet is known to cause goiter in fishes and may also be somehow related to HLLE.
Another cause of HLLE may be high nitrates. Frakes (1993) reported that nitrate levels higher than 160mg/l NO3-N might cause this condition.
In conclusion, there are possibly a number of causative agents when it comes to HLLE. The primary cause may be stress, including physical stress (e.g., irritants like carbon dust), malnutrition (e.g., lack of certain vitamins), mineral deficiencies (e.g., iodine), parasitic infection (i.e., Spironucleus) and poor water quality (e.g., high nitrate levels). The key then is providing your fish with as stress free of an environment as possible, making sure to address the specific stress factors discussed above.
Good luck and happy fish watching!
References:
Bassler, G. 1996. Diseases in Marine Aquarium Fish. Bassler Biofish, Belgium, 96 pp.
Blasiola, G. C. 1989. Lateral line erosion. Pet Age December (1989): 19-21.
Collins, S. 1995. Dietary control of HLLE in blue tangs. Sea Scope, 12 (Summer): 4.
Frakes, T. 1993. Nitrate Menace? Sea Scope 10 (Winter): 1-2.
