You shouldn't need to cook canned fish, they are cooked after canning at the factory, which is why they are shelf stable for years.

You shouldn't have to, but you would be taking a massive risk, and risk becoming a medical statistic when worms grow and multiply, also entering various organs.

In me, canned tuna caused major problems that required antibiotics to resolve after conducting thousands of dollars of tests. The tuna evidently had certain highly inflammatory bacteria. I consider myself lucky that the antibiotic worked at all.