Hyack Hyack:
And make sure it's being sold by a reputable retailer, someone you can trust.
Exactly. The grocery store is not a reputable fishmonger. They say their staff are 'highly skilled' and 'concerned with your health', but that is just a lie. Their staff are barely trained, and don't know what a worm infestation looks like. Nor would they know how long to freeze fish before it's safe from worms.
Get to know a good fish store. I tried some of the fish imported fresh from Iceland, and it is the best fish I've ever eaten! Superstore previously frozen farm raised Atlantic salmon just doesn't measure up.