As inexpensive as it is to feed fish, I tend to only use the best and freshest available -but not a doubt in my mind expired fish food would be eagerly consumed without issue. It's usually preserved with ethoxyquin and if unopened should be shelf stable for years. If it's been opened and fed, it's up to you. Probably perfectly safe, but again, even expensive fish food is really really cheap comparatively.

 

I'd use the recently expired stuff, but ditch the rest - particularly if it's opened. Once the seal is broken it will go down hill quicker so opened in 2016 is way out. Unlikely to be dangerous, but won't be good for them either.

 

If breeding, I would not use expired food. Especially if it had been open for a year.

For the average fish that I'm not too concerned about color and size. I wouldn't have a problem feeding a sealed expired food. Once the container is opened. You risk dust mites and tiny insects, like beetles, contaminating the food.

For bottom feeders or feeding local pond fish like bluegills, I'm sure they'll be happy with anything they can get. If the food smells funny don't touch it, or continue to breath the dust. I've seen food go bad and wouldn't be hard to imagine it making a person sick from mold or fungus spores.

 

This is my personal practice...

Fish:

If the food looks or smells bad? Don't use it. If it seems okay? Try it.

Anything with low/no moisture content is usually fine for a couple years after arbitrary expiration or sell-by dates. Stuff like flakes, super-dry pelletized foods, powders, micro foods. Anything more complex can be more tricky as it begins to break down and oxidize.

Freeze-dried worms and the like last a looong time. Way longer than any expiration date suggests.

I've never had frozen food on-hand for more than a couple months. That's in a few decades of keeping fish. So I've never had to contemplate freezer burn or anything like that.

Shrimp & other inverts:

If it's shrimp food? Totally ignore expiration dates and use your own judgment. There are some companies selling shrimp food claiming it goes bad in just six months. One claims its pressed barley goes bad in about a year. Reality? It's good for easily a decade or until it starts to break down.

I make and sell shrimp food. So I tell people to use their judgment because that's what I do. I know my foods last for years based on testing and in-depth experience and I don't use any preservatives. Others, with a few exceptions, can last just as long. Shrimp-specific foods are especially subject to hype, price-gouging and fearmongering so it's best to exercise good judgment unless you just like throwing money away.

Shrimp are detrivores and live off rotting waste in the wild. People get uptight with them sometimes and forget that.

 

Sweet, that was very informative. Thanks for the replies everyone!