Chickens should love them, bones and all, either cooked or raw. I don't know how big the fish are or how many chickens you have, so I can't tell you haw many to feed at one time. Maybe freeze or refrigerate some and feed a little at a time. You can either chop it into small pieces or just toss it in there. I've seen chickens cut a mouse, snake, or frog into bite-size pieces with their beaks. Depending on how big the fish are, you may have a skeleton to deal with later.
There are two different things that are likely to happen when you give them the fish. They immediately go on a feeding frenzy or they are hesitant to eat it. Let me tell a story to demonstrate.
A few years ago I gathered a small yogurt cup full of corn ear worms when I was processing corn for canning. I dumped that cup or worms out near a group of free ranging 10-week-olds. Those chicks were curious but weren't sure what was going on. A few gradually and cautiously crept closer and closer. A worm wiggled! Run away! Run away! They didn't run far and gradually started sneaking up on the pile of worms again. Closer and closer. A worm wiggled! Run away! Run away! This went on a few times until finally a bold chick grabbed a worm and ate it. That's all it took. That pile was gone in less than 30 seconds.
