Ulcers

Lesions on a fish's body, usually typified by an erosion of the skin, reddening, and often surrounded by a white mucus or fungus. Ulcers are usually caused by a bacterial pathogen infecting a wound on the fish's body.

Under poor conditions, or through bad handling, aquarium fish are prone to ulcerations, and if the problem is not treated the bacterial pathogens can multiply and spread to other fish. Some aquarium species such as rainbow-fish and small gouramies can be particularly prone to ulcerations.