Dropsy

Symptoms
This disease is characterised by a swollen or hollow abdomen (Ascites). A concentration of fluid in the body tissues and cavities causes the fish's abdomen to become swollen and appear bloated. Swollen areas may exhibit a 'pine-cone' appearance caused by the fish's scales sticking out. You can best see this by viewing your fish from the top. Fish may also stop feeding, appear off-colour, become listless and/or lethargic, have sunken eyes, and hang at the top or stay at the bottom of the aquarium.

The condition affects the fish's internal organs, ceasing proper function.

Gouramies, Cyprinids (barbs, danios, goldfish etc), guppies and bettas are prone to this disease.

Causes
Dropsy is fairly easy to diagnose non-specifically, however, it is much harder to diagnose the cause. The main cause is bacterial infection. The causative agent may be introduced through food or dirty water. Edema second to kidney failure or ascites due to liver or heart failure are other possible causes.

Treatment
Dropsy is not very contagious; however, if a fish is diagnosed with dropsy, it is important to remove it from the aquarium because the infected fish will contaminate the separate water and end up dying. If there are multiple fish, treat the afflicted fish in a specially established "sick tank" (Quarantine). Dropsy can spread from the ill fish, possibly causing stress among the other fish in the tank community. This extra stress may make the others vulnerable to dropsy or other forms of disease.

Treatment may consist of antibiotics targeting the causative agent. They work best in the very early stages of dropsy. A more hands-on approach is to raise the aquarium's temperature a few degrees - slightly higher than usual. Adding Epsom salts (Magnesium sulfate) to the water (at a rate of 20 mg/L) helps to encourage the fish to expel unnecessary damaging fluids.

Prognosis
Prognosis of fish dropsy is not good. By the time the fish has swollen up enough that the scales begin to raise, the internal damage may be too extensive to repair. Most cases of dropsy are fatal. However, if the fish is placed in a quarantine tank and treated with a broad spectrum antibiotic or a bacterial remedy from any aquatic sales shop, then the fish can make a full recovery in less than a week.

Prevention
Maintaining water quality is always extremely important. It should always be checked first, because it is often the cause of disease in aquarium fish. Frequent water changes can work to prevent the spread of disease by "watering down" the concentration of disease agents, and by reducing stress on the tank occupants.

All tanks need a 10-25% water change on a weekly basis. The best method of changing water is siphoning the water from the bottom, removing debris and fecal matter from the gravel.

Always feed fish from reliable sources and use high quality food. Varying diet is also important.

Honestly, that looks pretty cool. Makes the fish look more badass.

It seems to me this affects fish that have a labrynth organ OR eat so much that that also gulp air.

The protruding scales are caused by internal pressure from their tissues filling with fluid from a bacterial infection, not air. This is apparently very painful for the fish. I have head fish with Dropsy and once they start to blow up like the picture there is usually no hope. I usually euthanize them if they do not improve in a day or two.

Funny thing about pain in a fish. Apparently theres been a huge debate in whether fish actually feel pain. There has been research suggesting that they do react to higher temperatures but not actual pain caused by penetration. Oh well, better to kill the fish then to do nothing else. The thing is that, how did bacteria get into the water first of all?