Even though we fail to perceive it, every animal is an individual personality and show specific personal traits, even among the same species. There could be two cats of the same breed, may even be from the same litter but can have completely different personalities.
Animals have their own individual thoughts, feelings and preferences. Your cat may not fall into the stereotypical “cat love fish” category but that does not mean that there is something wrong with him. Just as how we prefer certain cuisines over other, tolerate some and totally dislike a few, cats also have individual preferences.
To put it simply, your cat has food preferences and fish is definitely not one of them. If your cat’s initial culinary experience with fish had been a disaster, he might have developed a dislike for it. If he has tasted other meats that he likes, that may also be a reason.
Additionally certain pet foods have flavoring agents in them that aim to enhance the taste of the dry food. It is possible that the raw fish that you are offering does not have these incentives that the pet food seems to offer. Whatever be the reason for this, his choice can be accommodated.
Cats are generally open to trying new foods. So, if he is being fussy then. check with the veterinarian to make sure all he gets all his essential nutrients from his diet. The vet may suggest additional supplements or treats if necessary to compensate of any dearth of nutrients. As long as he is healthy and playful and is medically sanctioned fit there is no reason to be concerned. Let him dislike his fish in peace!