What are your water parameters? (ammonia, nitrite & nitrate). How long have you had the bristle nose? What else can you tell us about your tank---size, all fish & how long you've had them, water change schedule?
What, besides veg on a fork, are you feeding? He looks nicely chubby. I see what you mean on his upper side but I agree with OG, not alarming. Do a few water changes within a few days & see if that helps.