I'v been using a fish "pellet" for going on 10+ years now.
A lot depends on the feed that you are already feeding and what out come you will see.
If your using a "low end" vegetarian type feed and you start supplementing with a good fish "pellet" that has at least one type of animal proteins in it you could see a world of difference in you fowl.
Anything from improved feather growth, better sheen to the feathers, improved weight gain, better egg production, less feather pecking, less cannibalism etc.
I myself use a high end fish pellet that is designed for carnivorous fish and I saw a difference in my fowl even with me feeding a mid to upper end poultry feed that contained animal proteins.
