some info from other sites. I'm only pasting small portions from entire articles:
http://fish.turquoisewave.com/index.php?option=com_content&task=view&id=43&Itemid=38
Remember that salt of any kind (epsoms, NaCl, sea salt) is not a cure for dropsy. All it can do is let you doublecheck that your fish isn't constipated and maybe buy you some time if it really is kidney failure.
> Note that large fish and small fish do not react the same to diseases,
> especially with dropsy symptoms which may have come on slowly. Small
> fish often die before you've had a chance to research cures or methods
> of euthanizing.
Larger fish can live quite a long time (months).
Valuable larger fish (i.e. show koi or family pet oscars) can be treated by a vet. According to Untergasser and Manual of Fish Health, the best thing to buy time for a fish in kidney failure is aspiration of the excess fluid from the abdominal cavity with a syringe. A vet or someone trained in fish anatomy can do this procedure without puncturing internal organs. I wouldn't try it myself...
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http://www.fishchannel.com/fish-health/disease-prevention/dealing-with-dropsy.aspx
Dropsy is not a specific disease but rather a symptom of a deteriorated health condition.
The visible swelling is the result of a tropical fish not being able to regulate the amount of fluid in a part of its body, typically the abdomen, and specifically, most often the visceral cavity that houses a number of organs such as the stomach, intestines, gall bladder and kidney. The failure to regulate fluids is a symptom so there is usually some other disease involved that starts the process..........
At the same time, there are also theories that connect dropsy or the abdominal swelling we typically associate with dropsy with actual disease-causing pathogens: internal bacterial infections, parasites, viruses and tumors.
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http://www.oscarfishlover.com/helpful-articles/swollen-abdomen
Because a bloated, swollen abdomen is a symptom, not a disease, it can be extremely difficult to treat.
Unfortunately, in many cases, Oscars that develop severely swollen abdomens do not survive. By the time the symptoms have shown themselves, it is too late for the fish. There are various reasons why a fish will develop these symptoms.
In some cases, there is a genetic problem with the fish. The fish may well be okay for the first few years, then it starts developing problems in the abdominal area. There wouldn't be any cure for this condition.
Fish can develop tumours which will cause swelling in the abdomen. Unfortunately, the only treatment for this is surgery which would probably be futile as the fish would probably not survive.
Internal bacteria or viral infections in fish can often result in them having a swollen abdomen/body. Quite often the eyes bulge and the scales are raised. This is sometimes referred to as "dropsy" This is an extremely serious condition. Remember that dropsy isn't an actual disease, it is actually a symptom of something more serious that is wrong with the fish. For this reason, it is very difficult to treat. If caught early, antibiotics might help. However, off-the-shelf may medication not work, you may have to seek professional advice and have injections administered. Again, the chances of this resulting in a cure are quite slim.
If your fish develops a balloon shaped abdomen that is soft and not hard like a tumour, this could possibly be internal organ disease which can result in fluid buildup in the abdominal cavity....
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This article is primarily about a different appearing infection than common Dropsy, but a little more than midway through, it gets to Dropsy:
http://www.oscarfish.com/article-home/healthdisease/116-jss.html
There is interesting reference to veterinary cultures used in identifying the causal agent, and also a medication called
Seachem Neoplex helping with this fish's cure.
just searched for some remote straws.
you do live in a big city, sometimes a vet is interested in trying their hand at less common animals.
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This site has dropsy xray images:
http://www.fishdeals.com/fish_diseases/dropsy/