If your cat eats a fish-flavored diet, then they might have somewhat fishy breath after they have eaten. However, if the fishy smell about your cat is very strong or persists, then it’s important to pay more attention.
Try and pinpoint where the smell is coming from. If your cat has persistent fishy breath, dental disease is likely. A fishy odor around their rear end is likely caused by their anal glands. A general fishy smell over the whole body indicates skin issues. Contact your veterinarian for a checkup so that the necessary treatment can be given.