No idea what did him in. Had him about 4 or 5 months and was feeding him frozen brine and mysis which he did eat. Noticed earlier today he was trying to hide in the back of the tank so I got him to the front and put him in a small quarantine floater I have. Fed him some brine while he was in there and just about 20 minutes ago he started giving the "I'm about to kick the bucket" fish signs.

RIP little buddy.

really sad, but I was told that most mandarin that are kept in captivity without enough copepods only last about 6 months and then suddendly die.

The woman who told me that said she knew 3 persons who have tried to keep them and each time they died within 6 months suddendly. I did not beleive much of it but your story makes me wonder if it is true.

Did you have enough copepods and liverock?

Also we must not forget that often we take the largest fish that we see and those are always wild cought (almost always) so that means they might be quite old already. Put that on top of the stress and unappropriate food and then the life spawn might be reduced quite a bit.

Your fish might have been already 10 year old when you got it?