Symptoms of fin congestion often include dilated blood vessels in the tail and fins of the fish. They appear as red blotches on the trailing edges of the fins. This condition occurs more often in goldfish that have long fins.
Fin congestion often is a sign that the water quality is poor. The treatment is to do a 25 percent water change every few days until the symptoms clear up. An antibiotic treatment can be added if the symptoms do not clear up within a week.