My Oscar fish has hole in head disease & white eye. What to do?

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.

The addition of live prey may have introduced parasites into your aquarium. It is also possible it was pre existing and an unknown stressor may have triggered active infection. Regardless, now you have to treat. Check water quality first. Poor water quality is a major cause of illness and it can also complicate any condition. Test a sample at home with a kit or submit a sample for testing. Most pet stores or aquarists will do this for free or for a nominal fee. Ammonia and nitrites should be 0 ppm (parts per million). Nitrates should be 40 ppm or less but for HITH, try for 10ppm or less. Perform partial water changes using aged or conditioned water that is temperature and pH matched to prevent shock and further stress until water parameters are acceptable. Metronidazole is the treatment of choice for HITH. It will kill Hexamita which is the parasite associated with HITH. You can purchase metronidazole for tanks online or in the aquarium section of most pet stores. Follow label directions carefully. Remove the charcoal from the filter during treatment. A broad spectrum antibiotic should also be used to prevent secondary infection. If you have other fish in the tank, monitor them for similar symptoms. A proper diet is also critical. A vitamin and mineral deficiency may predispose a fish to this condition. Use a fortified pelleted diet. You can soak food in garlic juice (or GarlicGuard by SeaChem) to boost the immune system and stimulate the appetite.

Add an airstone or two or a bubblewand. Either will increase oxygenation. Warm water does not hold as much oxygen and cool water, so it could be stressing your Oscar. As long as he can fit the Tetras, or other tank mates, in his mouth, he will likely continue to eat them.

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.

Without an image, it is difficult to make detailed recommendations. In general, maintain pristine water quality and chemistry. Monitor for elevated ammonia or nitrite levels and perform partial water changes as needed. Use only conditioned water that is temperature matched to prevent stress or shock. Consider adding in a second antibiotic, such as Kanamycin, to treat gram negative bacterial infection. When treating the tank, be sure to remove the carbon filter insert during treatment.

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.

If you have an activated carbon filter insert, remove it or it will filter out the medication. Confirm adequate water quality and chemistry since both can impact health and healing. Consider adding a broad spectrum antibiotic to treat infection. You can purchase products such as Kanaplex or Maracyn in the aquarium section of the local pet or fish store. Follow label directions carefully. Plain aquarium salt (NOT table or Epsom salt) can be used at 1 teaspoon per gallon of water to reduce stress and aid in recovery.