I've read of the idea. Apparently it works for some people. I have read of other people using food meant for fish.Oh, that's true. I didn't think of that.
I know a guy who feeds his girls cat food in addition to regular feed to up their protein. Anybody have thoughts on that?
I've personally used turkey starter or gamebird starter for the same purpose. They can have a protein level almost as high as cat food, but every time I priced them at my local store the turkey starter or gamebird starter was a better deal than the cat food or the fish food (I was comparing dollars per amount of protein, not per pound of food). That is something that may be different in different places.
You could also check the bottom of your freezer, to see if there is any meat or fish you don't want to eat (freezer burned food can be safe but no longer appetizing to people.) That could be cooked up and fed to your chickens. Or they would probably be fine eating it raw, if you prefer to give it to them that way.