If the fish was from the ocean it would have lots of trace elements that might be beneficial but I think that with fresh water fish this is less likely, the protean will be good but you do not want to attract predators.
It helps if you are putting in several at a time, that way you will not have one that gets picked on too bad. They should be old enough that they are feathered out but still way smaller than the old birds. That way the oldies have trouble running them down. IMHO.