never seen it before but from the ingredients it looks like a great food, and the protein levels are good for the chis and the spaneil.
like wiht any food introduce it very slowly, fish can sometimes be a little rich on the tummy, so introduce more slowly than you would before. and watch for loose stool, but otherwise it might be worth a try.
your other option if everyone likes the chicken soup would be buy fish oil capsuls for people, for sammie open 1 capsule and add it to his food, youll see the same effect.
id start out with 1 every other day and see how it goes, eventually you could go up to up to 1 every day if needed, but you should see an imporvment on that too!
its not the fish itself that helps, its the omega 3 from the fish oil.
and welcome aboard Ruby