Hi, here's why no dry: The Truth About Dry Cat Food from Blakkatz
I would not feed my cats dry, for their own health. Any claims about dental health and dry are just nonsense - in fact it coats the teeth and gums with greasy carb deposits, which are very damaging.

And here, sorry, this is not for the faint-hearted:
Toxic Pet Food

And here's a great food, if you're in the UK or Ireland, and don't want to go raw yet: Lily's Kitchen • Organic Pet Food, Holistic Pet Care - Certified Holistic Pet Food • Organic dog food recipes • Organic cat food recipes • Lily's Kitchen are ethical producers of organic, holistic, pet foods providing optimum nutr
You are right to look for minimum 60% meat content, (not derivatives) but I'd only feed fish once a week or so. It has a high mercury content, which is a contaminant, thanks to our polluted seas.
I feed my two kitties raw food now, after going through a halfway house of Lily's, which they adored. But they adore their raw meat even more, as their jaws and teeth are getting that longed-for exercise, and I'm secure in the knowledge that their teeth are being cleaned the natural way!

Oh, and, sorry for sounding negative about everything, but don't mix dry and wet food, if you are feeding dry. The dry will undergo a bacteria explosion when it encounters moisture of any kind. This is a breeding ground for bugs. Even stored in the fridge, dry food should not be moistened.