can't totally answer your question, but some ideas come to mind, as in
how
long did you have it, versus how long it was supposed to live... it may
have
been old age... or, it's even likely that it got an internal parasite if
there were any fish introduced in the last 2-3 months....

I don't know how old but it wasn't that big. (I know, that's not always
a great way to figure out age). I think he's been in the tank longer
than that and he was the last purchase.

but I've seen it pretty regularly that after a fish dies, the owner will
do
an autopsy to see if there were blockages in the intestine, digestive
system, and urinary tract, which are the three biggies....

Hmmm... I was thinking about doing that. I haven't yet decided though.
Although, he's frozen now so I might have missed the opportunity.

Thanks for the comments.

-Ben

personally, I never can bring myself to doing it... I'm somewhat attached to
them, had them for years, and just can't do it...