Nitrite can be toxic at levels as low as 0.05 ppm, and 200 ppm of nitrates is way outside of the realm of healthy, unless 200 is a typo and it's supposed to be 20. I should have asked for tank size and how many of each type of fish as well as the other questions. If you could provide that it would help.
Okay, to start you need to do some water changes, assuming the 200 ppm nitrates. If you change too much water all at once it will be a shock to the fish and they will die, so start small. Start by draining about 10% of the water in your tank and replacing it with fresh water every day at about the same time, until the nitrates are below 20 ppm. Regardless of what's going on with this gourami it won't heal well, if at all, at 200 ppm of nitrates. This will also help getting the nitrites down.
Now for the gourami, that second pic helped a lot actually. I've narrowed the cause of the wound to A.) a wound started with a bacterial infection that just expanded and deepened until it penetrated to the internal body cavity, or B.) a larger parasite burrowing into the body. The big question is what is that yellow thing. It's not like any tumor or cyst I've ever seen, and it's awfully big for a parasite in an aquarium. If the cause is A. then it very well may be an organ protruding from the wound, most likely the end of the right lobe of the liver. If it's B., then it may be the parasite itself (?). In either case, I don't see how we end up at the picture in your first post, though, so I'm stumped.
I wish a coupla more folks would take a look.
WYite