Here is a post on dropsy.
Dropsy is not a disease in itself, and can stem from so many different conditions. The root of the problem would have to be known to figure out if it is contagious.
I have had limited success treating with Maracyn-Two for dropsy. I have had a few fish with dropsy, but the fish with symptoms, have been very spread out, in my case, not a contagios disease.
Might also want to check into internal parasites, this can also cause dropsy like symptoms.
Dropsy of Aquarium Fish
Bloat, Malawi Bloat
Protrusion of scales, distended abdomen, pop-eye
Dropsy has several possible causes: poor water quality, poor food quality, bacterial infections, intestinal flagellates, excessive proteins (especially to purely vegetarians)
Longer periods of stress can weaken the fish's immune system thus enabling the bacteria to enter the fish's body. At this stage, it becomes increasingly difficult to remedy the situation. The disease begins with a bacterial infection of the intestines resulting in the excretion of slimy fish wastes. In the course of the disease, parts of the mucous membrane of the intestines come off. They stay at the anus of the fish. Even if the fish keeps taking up the food, it cannot digest the food anymore leading to the malfunctioning of the internal organs. The amount of water the fish takes in then cannot be expelled and the excess liquid gather in the body cavity resulting in the protrusion of scales and eyes.
Excessive proteins can also cause bloat among fish, mbunas most especially as the fish cannot effectively digest the proteins in their stomachs. Herbivorous fish have longer digestive systems that are not designed to digest excessive proteins in comparison to the carnivores' shorter digestive system. Do not feed your herbivorous fish foods that contain too much protein. For more information about foods and their nutritional values, please check this topic
Epsom salts, metronidazole, kanamycin sulfate
Treatment may not be effective as the disease itself is internal making it difficult to treat and determine the exact cause.