Hello Jeremy,
You can find Anisakis in fish that comes from the ocean. You would not find it in river fishes. Also the ocean fishes produced by aquaculture come from waters that are 100% controlled, hence you know that the fishes haven't been in contact with marine mammals (the final host of this parasit).
If you fully cook the fish or freeze it for 48h, the bug dies, but in case of allergy, that would not solve the problem completely.