Symptoms: Fins may appear ragged and split. They may also seem clumpy, somewhat resembling melted plastic.  The bacteria infection can progress to the point where it completely erodes fins and tail, eventually moving to the body of the puffer.  Secondary fungal infections may be present as well.

Treatment: Remove new carbon from your filter.  Administer antibiotics.  Maracyn-two, Trisulfa, E.M. tablets, or tetracycline. Follow the directions on the package.  Aquarium salt is also helpful. (roughly 1 tablespoon per 5 gallons for freshwater puffers, temporarily)  Treat any secondary fungal infections that may have taken hold due to the primary infection.  Since this condition is contagious, quarantine the tank and be wary of contaminating other tanks via nets, hands, etc.

Background:  Several bacterial infections can cause degradation of the fins and tail. Pathogens include Flexibacter columnaris, Nocardia, Mycobacterium, Pseudomonas species.  Infection usually takes place as a result of injury or poor water conditions.