I think any fish is okay as long as it’s wild and preferably a young type of fish. Farmed fish are fed trash, including antibiotics, and swim around in their own waste. You should be able to find some wild Alaskan salmon in the freezer at the supermarket. I’m not so sure about fresh, but it’s not actually fresh anyway, is it? They freeze it when it’s caught and then defrost it at the fish counter, so I don’t see the difference in buying it straight from the freezer myself.