Hello, this is definitely a male guppy and that is definitely dropsy. I would remove the fish from the tank soon as you can, could spread to other fish. Can also try and treat him, and for future at first sight of dropsy can jump right on it. A rebound in health is unlikely but possible. Get him in a bucket with an air pump at least for a quarantine tank but with a heater would be better. Now need to give him an epsom salt bath. In a different bowl the ratio is 2 tablespoons of epsom salt to 1 gallon of freshwater. Don’t have to use a full gallon for a small fish. Place the fish in the bowl for 25-30minutes trying to get the temperature as close as possible to the quarantine bucket and move air stone to bowl from bucket. Then place the fish back into the bucket and bring back the air pump.