I think you would be just fine posting any additional pics in this thread since it's related to your bichir passing.
I don't know anything to help diagnose what the problem was and it's always possible for a future hobbyist or someone familiar with doing necropsy on a fish that sees something out of the ordinary.
Maybe
Josh's Fish might have some insight since he wrote the book on bichir's and might have contacts that could help out determining what was wrong.
Well Chips died. I did an autopsy because he simply would not sink and, sure enough, his left lung was STILL inflated. Everything looked fine (I've got a biology degree with experience dissecting fish) except for some ominous dark patches on the lung that kept re-inflating even when punctured.