Cats aren't supposed to get fish every day. Add other non fish flavors in.
You can switch it up. I often even mix flavors in a meal since I have multiple cats and open multiple cans.That's what I thought, but they really only have two non fish flavors and he won't eat the Chicken even though he likes chicken when we have it for dinner, even whines for it.
Also, if he's eating more than one can a day should it all be the same flavor it can they be different throughout the day?