Belching up the air bladder definitely comes from pulling them up from so deep. Generally those fish will not recover when released, even if they swim away. Crappies are touchier on this than perch are too, and may not even show a belched up air bladder when fatally affected and they swim away. It is the fish version of the "bends". In waters as deep as 30' some estimates put released crappie mortality from this at close to 95% whether or not they show any indications. In some Texas waters as a result it is illegal to release any crappie caught during parts of the year when the schools tend to be that deep. So this is a concern all over.