I feed a LOT of fish to my adult chickens. Bones and everything. Cooked and raw. They don't have any problems with it. They eat the fish guts & fish heads, too.
ETA: mine won't eat the spine and large bones - but they'll pick everything off them. The small bones, they polish off. Small fish bones are actually pretty easy to digest. I eat them, too.
Edited by feathersnuggles - 2/1/10 at 9:51am