When you push against the flesh and it flakes off then it is cooked. No worms in fresh fish. Raw fish is always eaten in all parts of the world used to be predominantly in Japan.
Wives tail, no tapeworms in your fish. Is it a pink kind of fish, like salmon? the best way is to poke a small knive in and part the flakes, if they part, it's cooked. Fish only takes a couple of minutes on each side.