I've had a fresh water mussel co-habitating with 3 goldfish for over 2
years. Today I've come home from work to find the mussel's shell (some 5 to
7 cm's across) competely empty and a small piece of it's flesh about the
size of a pea sitting on the bottom of the tank. Is it possible that one of
the goldfish attacked and subsequently ate the mussel or is it possible that
the mussel has been dead for some time and the flesh has rotted away to a
point where this small piece has come away from the shell? Or is it
something else again? Quite a shame really as I used to enjoy watching it
feel and move around the tank for food.

Thanks in advance.