No fish, no itch!
I've tried quite a range of different foods for my 1.5yo kitteh, and was happy to find a food that didn't even use fish oil.
The issue with fish is mine, not the cats', but since we switched to 'Happy cat' she no longer gets loads of leftover crumbs stuck in her chin fur (which would cause her to scratch but also make sores worse..), and this might just be a coincidence, but for months she was scratching herself up quite badly (all over, not just chin) and causing sores, but she's hardly scratched at all since starting this food, so smiles all round!