Imagine being the last owner of Hanako, that 226 year old Japanese koi that was spawned in 1751 and died in 1977. A fish that outlived 7 emperors. A fish that survived the Second World War. And she dies in your care. I would never recover.
I would find peace in that she felt comfortable enough to finally rest in my company. Fish remember faces and voices of their caretakers. Perhaps she loved the last too much to watch them die before her, too.