We keep small "mosquito fish", little orange minnows, in all our outdoor water features to eat mosquito larvae (they also eat some of the algae to keep the water clearer). We put them in our little ornamental pond, in pots where we keep waterplants, and in the little tubs where we grow azolla for feeding to the chickens. We've fed them a few of the extras when the population gets a little large, and they will certainly eat them.
If your goal is to produce some kind of animal protein to feed your chickens, in anything like an efficient way, I think you're much better off culturing soldier grubs, meal worms, or something similar. Maybe even compost worms, though they won't reproduce as quickly. I don't think there's any fish that will grow as quickly or reproduce as efficiently as an insect. You'd be producing much more biomass quicker and more efficiently--and besides, insects, grubs, and worms are a perfect feed for chickens, to which they are already well adapted.
But if you're wanting to raise minnows or something as a hobby for it's own sake, there's nothing wrong with feeding some of the surplus fishes as an occasional treat. (There is the issue some people raise that feeding excessive amounts of fish, while not unhealthy for the hens or the egg-eaters, can give the eggs a subtly "fishy" taste that seems to bother some people, but that wouldn't be a concern in the minor quantities you're talking about.)
