My goldfish is suffering from a disease. The symptoms are an enlarged stomach, loss of appetite, bulging eyes(both), tail up when floating, gasping for breath(mouth rapidly opens and closes) and constipation. One of my other fish had these problems and died. Before he died, we called Petsmart (where we bought the fish) and were told that either it couldn't get enough air or it was too old. It was two years old and Petsmart believed that age was the cause. However, this fish is about six months old. We have not put any new fish in the tank, in fact, this fish is the newest one. It does not seem contagious as the other fish in the tank is/wasn't affected by the other fish's problem.
Sorry but my practice is limited to dogs and cats. vetcare