Fish should never have the so-called "fishy" smell, which actually comes from bacterial decay. It is best to get live fish. The second best choice would be frozen-at-sea fish, often marked FAS. Refrigerated fish are generally a poor choice, especially for timid buyers who are hesitant to demand a chance to smell the fish prior to purchase. Avoid fish with any discolored area. Do not store unfrozen fish for long.
Canned fish are often good, but very different in taste, and selection is limited. Canned salmon and anchovies are particularly high in calcium, because the bones are softened by canning and are eaten with the flesh.
While it is generally unwise to eat any fish raw, wild freshwater fish are particularly likely to carry parasites that can infect humans.
Note: the names of fish vary around the world. Also, many different fish are often sold under the same name if they share roughly the same appearance.