Does anyone know why a fish swells up?

Dropsy

Symptoms

This disease is characterised by a swollen or hollow abdomen. Swollen areas may exhibit a 'pine-cone' appearance caused by the fishes scales sticking out. Fish may also appear off-colour and listless, and may stop feeding. The swelling caused by this disease may often be mistaken for a pregnant or egg-carrying fish. Gouramies and Cyprinids (barbs, danios, etc) are prone to this disease.

Causes

Dropsy is a condition with several possible causes. It may frequently be caused by internal infections by a number of different bacterial species. Viruses have also been associated with the disease. Poor water quality and/or diet may trigger the disease. If the problem has been caused by permanant damage to the kidney, then treating the infection will not eradicate the symptoms.

Possible cures

This disease must be caught early to maximise the chance of saving an affected fish, and even then the disease is difficult to cure. Previously, antibiotics prescribed by a vet were the only means of treatment for those countries (including the UK) where antibiotics cannot be purchased over-the-counter. There are now commercially available remedies which may help. These include Interpet #9 Anti Internal Bacteria and Waterlife's Octozin. The addition of salt (1 tsp/gallon) may also be beneficial.

Dropsy is not usually considered to be particularly contagious, so it should not spread to other healthy fish - dead fish should be removed immediately however, to avoid cannibalism. However, bear in mind that there is more than one cause of dropsy, so in some cases the infective agent could be contagious. It is preferable to carry out treatment in a hospital tank where available.

I think its dropsey. Dropsey is caused by either the kidneys or the liver failing, spilling fluids into the body. Organ damaged caused usually by an internal bacterial infection. Fish with dropsey are going to die, euthanize, there is no cure at this point. Melafix does nothing and is a waste of money and doesn't claim to cure internal infection anyway. Try an anti-biotic food for the others. Pesmart should have it. Don't medicate the water it will kill your beneficial bacteria. Always treat infection from the inside out with medicated food rather than outside in. Its very likely other fish have the priliminary infection, and need to be treated. Clean water is key. Never neglect your water changes.

if your fish has been living for months swollen, chances are that it is not droopsy. Sometimes fish just have organs fail, just like in humans, this leads to internal infections, build up of bodily fluids, exc. Do your best to care for this fish. I would medicate the entire tank with melafix, to ensure that there are no bacteria affecting the other inhabitants. It is also a good idea to add aquarium salt and to make sure that you are doing regular water changes with a siphon.

good luck!!

hahaha lol. its sad but i do know the answer to the question

its a rare gill/scale desese fish get. after a while it just kinda lays there on its side and if u leave it like that for too long the fish will die. also be sure to clean out the tank cuz the other fish in the tank can get it to. if the fish dies and u dont clean out the tank the other fish can still get it

Sadly, when a fish swells up like that there is really nothing that you can do as far as I know. I'm very sorry.

its called dropsy, its a internal bacteria disease it needs treatment. i used interpet no 9.