My fish has a hole in its head with white cotton. What's wrong?

It seems like there is an ulceration at the level of the gills. This may be related to a bacterial or fungal infection. Hole in the Head disease is possible as well. The exact cause of hole in the head fish disease has yet to be determined, but strong suspicion in terms of causes are parasite (Hexamita or Spironucleus infestation) or nutritional imbalances. Water quality must be checked and any abnormality corrected first. The treatment usually consists of taking a multi-faceted approach and includes includes the addition of the antibiotic metronidazole to the treatment tank housing the infected fish and making sure feeding is adequate. In cases where secondary bacterial infections are present, additional antibiotics such as Maracyn, Kanacyn, or Furan may be needed. When treating this or any disease, try to use a separate treatment tank and treat as soon as the first symptoms appear.

Check water chemistry and filtration. Sunny may have developed a bacterial or fungal infection due to the switch in environment. Clean water is crucial to resolving infection. Perform regular partial water changes. Use only aged or conditioned water that is temperature matched to prevent further stress or shock. Maintain water temperature between 75 F and 72 F. Minor infection maybe resolved using plain aquarium salt (NOT table salt). Salt is a great general tonic. It reduces stress, improves gill function and aids in recovery. Dissolve 1 teaspoon of salt per gallon of water in a cup of tank water and gently pour it into the tank. Treat until symptoms resolve. When performing water changes, use just enough salt to treat the water being replaced, not the entire tank volume. If necessary, you can use a broad spectrum medication if symptoms persist. Look in the aquarium section of the local pet or fish store for products such as Kanaplex, Maracyn or Lifeguard by Tetra. Follow label directions carefully and remove the carbon filter insert if indicated.

Looking at the photos, I agree that it doesn't look like the typical fungal infection. Generally you see multiple lesions and they tend to be fuzzy in appearance. I'm not sure what that is on the fin but it may be benign. I would recommend to call the pet store and tell them what you are seeing. Check to see if any of the other fish have become ill. Abnormalities on the fins can be fungal, bacterial or parasitic. There's also a change of a defect or injury. If the area is not really changing and your fish is acting normal, you may just monitor it. I hope this helps!

It could be early ich (white spot) infection or another infection (bacterial or fungal). To be safe, separate him into a quarantine tank and monitor for any change. You can treat for ich as you did it in the past if indicated. Bacterial and fungal infections have different treatments, so I would be hesitant to recommend a specific medication without more information or a definitive diagnosis. You can use plain aquarium salt (NOT table salt or Epsom salt). As a general tonic to reduce stress, increase gill function, treat minor infection of many types and to aid in recovery. This can be added to the quarantine tank at 1 teaspoon per gallon of water. Treat for 10-14 days then reassess the condition.

Test the water or submit a sample to confirm proper chemistry. Most pet or fish stores will test water for free or for a nominal fee. Correct any imbalances with partial water changes (30-50%). Use only aged or conditioned water that is temperature matched to prevent further stress or shock. Metronidazole is an effective treatment for HITH (hole in the head) disease. You can feed medicated food, treat the tank or use it for medicated soaks. Look in the aquarium section of the local pet or fish store. Follow label directions carefully.

Thanks for reaching out about your Oscar and including photos, but difficult to see the HLLE lesions due to too dark. The eye looks terrible and systemic antibiotics are recommended at the least. A veterinary visit is highly recommended to clean the wound and provide other possible treatments. The water quality must be kept pristine (pH, ammonia, nitrites, nitrates) to assist recovery. Antibiotics added to the water do not penetrate into the body, nor do fresh water fish drink, since osmotically water enters over mucous membranes (gills, mouth, skin) and antibiotics do not cross this barrier. HLLE causes can be multi-factorial including water quality, bacteria, parasites, carbon particles in activated charcoal (filters), low vitamin C, etc. Check and correct water quality, replace existing food if older than two months (vitamin C degrades quickly), see a veterinarian with fish experience. Good luck.

Thanks for reaching out about your fish and including a photo. This is a fairly large lesion and needs to be diagnosed and treated. Parasitic infestations and bacterial infections must be considered. Adding non-iodized salt at 1 tablespoon per 5 gallons for 3 consecutive days might provide some osmotic relief but is not therapeutic levels. A skin scrape and microscopic examination is needed to diagnose parasites is needed. Different parasites require different medications. Bacterial infections should be treated with systemic antibiotics through injections or oral medications, not water additives. Good luck.