With only the one picture to make a judgement, it is impossible to say. We generally like to start with water parameters, ammonia, nitrite, nitrate, pH, KH, temperature, and some info on activities of the fish.
I don't see any scales sticking out, which is a sign of kidney failure, which is good. I also don't see any ulcers, which is good. Most likely full of eggs, though spawning season is almost 6 months away, which is not good. I would say it is probably not a case of being fat.
Zone 7 A/B
Keep your words sweet. You never know when you may have to eat them.
Richard