I have an 11-year-old dojo loach which has no health problems all these years. Physically there are no changes in him, but he isn't eating and keeps keeling over. When I think that he's died, he'll move. Usually if I go away for a while I find him in a different position, but then he keels over again.I'm assuming that he's dying of old age. The other fish in the tank seem fine. As I said there are no signs on his body of disease. Any advice?