If you want to effect the taste of an animal by the food it is eating you need to feed that "flavor" to the animal for at least 3 months, it takes that long for the flavonoids to permeate the animal being fed.
This is known throughout the hog raising world and the most expensive hams on the planet (Iberico) come from hogs that eat acorns for the last four months of their life.
As for feeding fish to fowl, Ducks that eat fish, taste like fish. That means that the fish oil carried flavonoids permeate the ducks meat.
The same would happen to chickens so while you could do this you would probably want to think ahead so you changed their diet at least 3 months prior to butchering time.
To my taste buds,
free ranged chickens taste the best, they have such a varied diet they end up tasting like the chickens I remember from my grandparents farm.
The diet of grasses, bugs, past prime figs and vegetable and
fruit left overs, along with the hog feed they get when I give my hogs their supplement feed (they too are free ranging grazers)
We currently have great tasting eggs with deep orange yolks and I am sure the meat from the ones we cull will be flavorful.
Redhawk