and what makes it worse is that a lot of meat flavoured popular food like Felix contain fish , so it's not just a matter of avoiding fish flavoured varieties
All good things in moderation. A little fish every now and then isn't going I hurt. In fact, no fish at all is just as harmful, and eye need the Omega 3 that fish give. Too much fish, on the other hand, can indeed have adverse affects. My cats gets a teaspoon of fish - alternating between salmon and sardines - per week.
There's so much controversy about food. Raw feed/don't raw feed. All dry/no dry. All wet/no wet. Eggs/no eggs. In the end I stopped worrying about the controversy and spent some time researching cat biology and digestive systems. I built a balanced diet for mine, which a couple of vets have said is good. But it took a lot of time and effort.
We are off for lunch to a restaurant known for it's local caught fish. I'm sure some of it will find it's way back here. Willow is partial to a little white fish - never done her any harm.
Having said that she, and the others, won't touch sachets of fish flavoured cat food, never have. Odd that.