Hmmm I wonder if he has an internal parasite or flukes, that can be symptoms... getting thin, then eventually stop eating even tho they went for the food, and breathing problems. This is what happened to our Gold Saum, they were infected when they came from supplier, same symptoms, treated with Prazy and hell different fish now, breathing improved, not lethargic... started eating and gained weight... would never believe they were the same fish...