How do I treat this sore?


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One reader is concerned about a brown spot that has gradually grown on his Angelfish.

My Angelfish has developed a sore, which it’s had for about five weeks now. I’ve tried treating with Pimafix and Melafix, but without any success. It started out as a light brown spot but has gradually got darker and more red, and it has grown by about 2-3mm in the last couple of weeks — it’s now around 7mm in diameter. I do a 25-30% water change every two weeks as the tank is very heavily planted. Unfortunately, I do not have a quarantine tank, although the other fish are okay. What I should do?


Peter replies: We can see from the photo you sent that the fish has an open skin wound, which has breached the skin’s layers, exposing the red muscles beneath, and seems to have a thin whitish border. This is extremely typical of an ulcer.

Body ulcers in fish are caused by various infectious organisms, particularly certain bacteria and some viruses. Bacterial ulcers are more likely and in any case we have no routine treatments for viral diseases of fish. But I should add that physical wounds can also breach the fish’s skin leading to ulcer-like lesions. 

You mention having already used a couple of plant-based anti-bacterial treatments, and it’s certainly worth trying these sorts of medications, but unfortunately some bacteria are tricky
to eradicate with over-the-counter aquarium remedies. Instead, they may require antibiotics, perhaps given by injection, or with the food, or applied topically to the wound in paste form. Antibiotics would mean a trip to the vet. 

However, before heading to a vet, and assuming the fish’s lesion hasn’t deteriorated, then I think it’s worth trying one of the ‘traditional’ dye-based anti-bacterials from your fish store, such as an ulcer-cure or broad spectrum bactericide.

As you don’t have a spare tank to isolate the fish for treatment, read through the manufacturer’s advice regarding any possible harmful effects of their medication to ‘sensitive’ fish species, such as Clown loaches, that are sharing the same tank. If you still have no success, then I would suggest involving a vet. 

Be aware that this large breach to the fish’s protective skin layer carries the risk of further infections, and also renders the fish ‘leaky’ to the free movement of salts and water between its body and its environment. So secondary infections and osmoregulatory (salt-water imbalance) problems can occur. Had it been possible to isolate the fish, I would have suggested adding 2g salt (sodium chloride) to its isolation tank water, to help ease osmoregulatory stress, but I’m not keen on adding salt to the community aquarium just to treat a single fish. I should add that good aquarium hygiene is paramount to the healing process: the cleaner the aquatic environment, the less risk there is of secondary infections.

Preventing ulcers

While some types of bacteria (and viruses) can cause ulcers in perfectly healthy fish, often their appearance is a sign that the fish is stressed for some reason or has incurred a skin injury. 

Always consider possible underlying risk factors, such as poor aquarium hygiene; incorrect water conditions for the fish species in question; attack/bullying by other fish; physical injuries such as skin abrasion on rocks; skin damage caused by skin parasites such as Ich or velvet. If there is an underlying cause, even effective treatments may not work — and in some cases, simply by identifying and eliminating the source of any stress, the ulcer may heal by itself.