Well, we had some leftover salted cod fish. It wasn't expired, but no one felt it was safe for human consumption since it had been sitting in the fridge. It was probably safe to eat, but nevertheless no one would touch it. I rinsed off as much salt as I could and let it sit in water overnight then threw the whole chunk in to the Tilapia (and some to the goldfish pond as well). They fought over it like fat kids at fat camp being thrown Twinkies... Anyway, by the next day I came out and it was all gone.

I have also fed the fish "expired" bread. The goldfish seem to like that more than the Tilapia.