-oddly, they too can have too high or too low iodine in diet. not sure how to test but maybe worth researching online
-BPA in cans can contribute to condition but smaller cans of wet food contain less of this **whatever your stance on BPA**
-and PBDEs (fire retardants) can be in a high-fish diet. these apparently can contribute.
oddly, my own feline has some of these symptoms but my vet says his tests show high liver enzyme problems. damn tricky to diagnose but you are doing the best thing possible by keeping China high protein. been shown recently to have sizable benefit for longevity of felines, beyond what was even previously understood.