I certainly would not be afraid to use it to feed the fish. Odds are great that in the wild or even in aqua culture they eat a host of stuff that is probably worse than some expired food would be......surely you do not think all that food yur buying for them now is process in a 100% sterile and super clean environment. Heck there is even a limit as to dirtyness and junk that human food is allowed to be processed in. Feed it, if they don;t like its freshness and they refuse to eat it then throw it out. Odds are they will scarf it up.