Is not the worst fish in this sense. Cod is worse.
The real problem with tuna is that is an accumulator of nasty substances like mercury and also fast and nomadic by nature. This means that you can find Japanese tuna in California, or the Mediterranean, and this can be a problem.
Most of the fish parasites just turn into food after being cooked. Our stomach acid will not care. The number of marine fish parasites able to harm humans is very small. We are too hot for them. I could count all the major types with my fingers (I was surprised to learn (here) that Kudoa is a new problem in any case).
The real problem with tuna is that is an accumulator of nasty substances like mercury and also fast and nomadic by nature. This means that you can find Japanese tuna in California, or the Mediterranean, and this can be a problem.
Most of the fish parasites just turn into food after being cooked. Our stomach acid will not care. The number of marine fish parasites able to harm humans is very small. We are too hot for them. I could count all the major types with my fingers (I was surprised to learn (here) that Kudoa is a new problem in any case).