Dropsy is a symptom of some other underlying cause. It's merely the retention of fluid in the body cavity. It can be caused by many things. Kidney failure is a common reason and that could be just a single fish with bad kidneys. Notifying us isn't necessary unless you see a large number of these. I've never had a situation where this occurred in the wild in any large numbers. In fact, I've only seen 2 fish in this conditions in 27 years.