I feel so bad for you, I have raised several rats and they make really good pets. Is the breathing labored or does he have any tumors? From what I have read they don't have a very long life span (3 to 4 yrs). Most of mine have made it 2 to 3. I was told years ago by an old veterarian(sp?) that putting them in a blanket then a bag in the freezer was a very humane way of putting them down. I was told they just go to sleep and feel no pain. I have done this with a couple that were on their last breaths. I really feel for you. I love rats but won't have anymore (unless I save one from someone that doesn't want theirs like my last one, Patches) because they don't live long.