Identify & Combat Head and Lateral Line Erosion Disease in Marine Fish

| Updated: July 13, 2023
Purple tang with head and lateral line erosion disease (HLLE)

If you love keeping aquarium fish, you may have heard about or even noticed a condition in some of your fish that makes them look like they have pits or holes on their head and along their sides. This condition is called head and lateral line erosion disease (HLLE) or hole-in-the-head disease (HITH). It’s a well-known disease in both freshwater and saltwater fishes, but it mainly affects surgeonfish (tangs) and angelfish in marine ornamental fish, although it can affect other fish too.

HLLE is not only ugly, but it can also lead to secondary infections of bacteria and parasites. It can also affect the fish’s ability to sense vibrations in the water, which is important for their survival and social behavior.

Read on and we’ll explore the causes, symptoms, diagnosis, treatment, and prevention of HLLE in ornamental marine fish. We’ll also discuss some of the experts’ opinions and research on this disease, as well as some tips on how to maintain good water quality and nutrition for your fish.

What Causes HLLE?

The exact cause of HLLE is still unknown, and there are many factors that may contribute to its development. Some of the possible causes include:

  • Poor water quality: One of the most common factors associated with HLLE. Poor water quality can stress the fish and lower their immunity, making them more susceptible to infections and diseases. Poor water quality can also damage the fish’s skin and mucus layer, which are their first line of defense against pathogens. Some of the water parameters that should be monitored and maintained include pH, ammonia, nitrite, nitrate, phosphate, dissolved oxygen, salinity, temperature, and hardness.
  • Heavy metals: Some studies have suggested that exposure to heavy metals such as copper, zinc, iron, lead, and mercury can cause HLLE in fish. Heavy metals can build up in the fish’s tissues and organs, causing oxidative stress and inflammation. They can also interfere with the fish’s metabolism and immune system. Heavy metals can be introduced into the aquarium through tap water, food, medications, equipment, or decorations.
  • Nutritional deficiencies: Another possible cause of HLLE is the lack of proper nutrition for the fish. Some nutrients that are essential for the fish’s health include protein, fat, carbohydrates, vitamins, minerals, and trace elements. Some of these nutrients are especially important for the fish’s skin health and mucus production, such as vitamin C, vitamin E, vitamin A, zinc, iodine, and selenium. Nutritional deficiencies can result from feeding low-quality or expired food, feeding inappropriate food for the fish’s species or life stage, or feeding insufficient or excessive amounts of food.
  • Parasites: Some parasites can cause HLLE in fish by damaging their skin and mucus layer, allowing secondary infections to occur. One of the most common parasites that can cause HLLE is Hexamita spp., a protozoan that infects the fish’s intestines and sometimes migrates to other organs such as the liver and brain. Hexamita spp. can cause weight loss, lethargy, anorexia, white feces, head twitching, and neurological signs in infected fish. Hexamita spp. can be transmitted through contaminated water or food.
  • Bacterial infections: Bacterial infections can also cause HLLE in fish by invading the lesions caused by other factors such as poor water quality or parasites. Some of the bacteria that can cause HLLE include Aeromonas spp., Pseudomonas spp., Vibrio spp., Flavobacterium spp., Mycobacterium spp., and Streptococcus spp. Bacterial infections can cause inflammation, ulceration, necrosis, hemorrhage, pus formation, and systemic signs such as septicemia in affected fish. Bacterial infections can be transmitted through direct contact with infected fish or water or through wounds or injuries.
  • Other factors: Some other factors that may contribute to HLLE include stress from overcrowding, aggression, handling, transportation, or environmental changes; physical trauma from injuries or abrasions; genetic predisposition; use of activated carbon in filtration; exposure to stray voltage; or unknown causes.

What Are the Symptoms of HLLE?

The most obvious symptom of HLLE is the appearance of pits or holes on the fish’s head and along its lateral line. The lateral line is a sensory organ that runs along the sides of the fish’s body, allowing them to detect vibrations and movements in the water. The holes may vary in size and depth and may be filled with mucus, debris, or parasites. The holes may also become infected and inflamed, causing redness, swelling, or bleeding.

Other symptoms of HLLE may include:

  • Loss of appetite or weight
  • Lethargy or depression
  • Faded or darkened coloration
  • Cloudy eyes or eye lesions
  • Fin erosion or fin rot
  • Abnormal swimming or behavior
  • Breathing difficulties or gill lesions
  • Systemic signs such as bloating, dropsy, or septicemia

The severity and progression of HLLE may depend on the underlying cause, the fish’s species and immune system, and the environmental conditions. Some fish may recover from HLLE with proper treatment and care, while others may succumb to the disease or its complications.

How Is HLLE Diagnosed?

HLLE can be diagnosed by observing the fish’s appearance and behavior and testing the water quality and parameters. However, since HLLE can have multiple causes and can be confused with other diseases, it’s advisable to consult a vet or an expert who can perform more accurate and reliable tests. Some of the tests that can be done to diagnose HLLE include:

  • Skin scrapes or biopsies: Samples of the fish’s skin or tissue are examined under a microscope or sent to a lab for analysis. They can reveal the presence of parasites, bacteria, fungi, or other pathogens that may cause HLLE or secondary infections. They can also show signs of inflammation, necrosis, or degeneration of the skin cells.
  • Blood tests: Samples of the fish’s blood are analyzed for various parameters such as red blood cell count, white blood cell count, hemoglobin level, hematocrit level, blood glucose level, electrolyte level, and blood gas level. They can indicate the fish’s overall health status and immune system function. They can also detect anemia, infection, inflammation, stress, or organ failure signs.
  • X-rays or ultrasounds: Imaging techniques that use radiation or sound waves to create pictures of the fish’s internal organs and structures. They can reveal abnormalities such as tumors, cysts, abscesses, granulomas, foreign bodies, or fractures that may affect the fish’s health or cause HLLE. They can also show signs of organ enlargement, displacement, or dysfunction.
  • Water tests: Tests can measure water quality and parameters such as pH, ammonia, nitrite, nitrate, phosphate, dissolved oxygen, salinity, temperature, and hardness. They can indicate if the water is suitable for the fish’s species and needs. They can also detect signs of contamination by heavy metals, organic compounds, pesticides, or medications that may cause HLLE or other diseases.

How Is HLLE Treated?

The treatment of HLLE depends on the underlying cause and the severity of the condition. Some of the general steps that can be taken to treat HLLE include:

  • Improving water quality: Perhaps the single most important step in treating HLLE. Water quality should be monitored regularly and maintained within the optimal range for the fish’s species and needs. Water changes should be done frequently and carefully to remove waste products and pollutants from the water. Filtration systems should be checked and cleaned regularly to ensure their efficiency and prevent clogging. Chemical additives such as dechlorinators, conditioners, buffers, or stabilizers should be used as needed to adjust the water parameters. Water tests should be done regularly to ensure the water quality and parameters are within the acceptable range.
  • Isolating affected fish: This is another important step in treating HLLE. Affected fish should be moved to a separate quarantine tank where they can be treated and monitored more easily. The quarantine tank should have the same water quality and parameters as the main tank and should have adequate filtration, aeration, heating, and lighting. The quarantine tank should also be kept clean and free of stressors such as overcrowding, aggression, or noise.
  • Medicating affected fish: This is a step that should be done under the guidance of a vet or an expert who can prescribe the right medication and dosage for the fish’s condition and species. Some of the medications that can be used to treat HLLE include:
    • Antibiotics can kill or stop the growth of bacteria that may cause HLLE or secondary infections. Some of the antibiotics that can be used to treat HLLE include tetracycline, erythromycin, kanamycin, nitrofurazone, or chloramphenicol. Antibiotics can be given orally, topically, or through injections or baths. Antibiotics should be used cautiously and only when needed, as they can also kill good bacteria in the water or the fish’s gut, leading to other problems such as fungal infections or digestive disorders. Antibiotics should also be used for the full course of treatment, as stopping them early can lead to antibiotic resistance or relapse of infection.
    • Antiparasitics are used to combat the growth of parasites that may cause HLLE or secondary infections. Some of the antiparasitics that can be used to treat HLLE include metronidazole, praziquantel, levamisole, fenbendazole, or ivermectin. Antiparasitics can be given orally, topically, or through injections or baths. Antiparasitics should be used cautiously and only when needed, as they can also harm good organisms in the water or the fish’s body, leading to other problems such as toxicity or immune suppression. Antiparasitics should also be used for the full course of treatment, as stopping them early can lead to parasite resistance or relapse of the infection.
    • Anti-inflammatories reduce inflammation and pain in the fish’s skin and tissues. Some anti-inflammatories used to treat HLLE include acetylsalicylic acid (aspirin), ibuprofen, naproxen, meloxicam, or prednisone. Anti-inflammatories can be given orally, topically, or through injections or baths. Anti-inflammatories should be used with caution and only when needed, as they can also cause side effects such as bleeding disorders, ulcers, kidney damage, or liver damage. Anti-inflammatories should also be used for the shortest duration possible, as long-term use can lead to dependency or withdrawal symptoms.
  • Supplements are used to provide extra nutrients or benefits for the fish’s health and recovery. Some supplements that can be used to treat HLLE include vitamin C, vitamin E, vitamin A, zinc, iodine, selenium, spirulina, garlic, or probiotics. Supplements can be given orally, topically, or through injections or baths. Supplements should be used with caution and only when needed, as they can also cause side effects such as allergic reactions, toxicity, or interactions with other medications. Supplements should also be used for the appropriate dosage and duration, as overdosing or underdosing can lead to a deficiency or excess of certain nutrients.
  • Improving nutrition is an essential step in treating HLLE. Nutrition plays a vital role in the fish’s health and immunity, as well as their skin and mucus production. Nutrition should be tailored to the fish’s species and needs, as different fish have different dietary requirements and preferences. Nutrition should also be varied and balanced, as feeding the same food or too much of one type of food can lead to nutritional deficiencies or imbalances. Nutrition should also be fresh and high-quality, as feeding expired or contaminated food can lead to health problems or diseases. Some of the tips on improving nutrition for fish include:
    • Feeding a varied diet that includes pellets, flakes, frozen foods, live foods, vegetables, fruits, and algae.
    • Feeding appropriate foods for the fish’s species and life stages, such as herbivorous foods for surgeonfish or omnivorous foods for angelfish.
    • Feeding enough but not too much food, as overfeeding can lead to obesity, waste buildup, or water pollution.
    • Feeding at regular intervals and removing any leftover food after a few minutes.
    • Soaking dry foods in water or vitamin solutions before feeding enhances their taste and digestibility.
    • Adding supplements such as vitamins, minerals, trace elements, or probiotics to the food or water as needed.

How Is HLLE Prevented?

The best way to prevent HLLE is to provide optimal conditions and care for your fish. Prevention is better than cure, as HLLE can be hard to treat and may cause permanent damage or death in some cases. Some of the steps that can be taken to prevent HLLE include:

  • Maintaining good water quality and parameters by performing regular water changes and tests, using effective filtration systems, avoiding overstocking or overfeeding, and removing any sources of contamination or pollution from the water.
  • Providing adequate nutrition by feeding a varied and balanced diet that suits your fish’s species and needs, using fresh and high-quality food, and adding supplements as needed.
  • Reducing stress by providing a suitable environment that meets your fish’s biological and behavioral needs, such as enough space, hiding places, lighting, temperature, and water flow. Avoiding any factors that may stress your fish, such as overcrowding, aggression, handling, transportation, or environmental changes. Providing enrichment and stimulation for your fish, such as plants, rocks, toys, or companions.
  • Preventing infections by quarantining any new or sick fish before introducing them to the main tank, using sterile equipment and tools, and disinfecting any wounds or injuries. Treating any infections promptly and effectively with the right medications and dosages.
  • Monitor your fish’s health and behavior by observing them regularly for signs of HLLE or other diseases. Seeking professional help or advice if any problems are detected or suspected.

Final Thoughts

HLLE is a complex and controversial disease that has been studied and debated by many experts and researchers. There are many theories and hypotheses on the cause, mechanism, and treatment of HLLE, but none of them have been conclusively proven or universally accepted. Therefore, it’s important to keep an open mind and a critical eye when dealing with HLLE and to seek professional help or advice if needed.

We hope this article has helped you understand more about HLLE in ornamental marine fish and how to prevent or treat it. If you have any questions or comments, please feel free to contact us. Thank you for reading this article, and happy fishkeeping!

Shane Elliot Author Image
Shane Elliot

Shane Elliot is a pet lover and a coral enthusiast. He has been keeping saltwater aquariums for over ten years and enjoys sharing his knowledge and expertise with other hobbyists. He writes about coral care, fish compatibility, aquarium equipment, and more. He also covers topics related to other animals, such as dogs, cats, horses, and reptiles. Shane works as a freelance writer and editor when his menagerie of pets allows it.

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