Freshness is the single biggest factor in how seafood tastes and how good it is for you. A few simple checks at the point of purchase tell you almost everything you need to know.
The five-point freshness check
Eyes should be clear, bright and slightly bulging — never sunken or cloudy. Gills should be vivid red or pink, not brown or grey.
Fresh fish smells clean and like the sea, never sour or strongly 'fishy'. The flesh should be firm and spring back when pressed, and the skin should look shiny and metallic, with scales tightly attached.
Whole vs. cut
Whole fish are easier to judge for freshness than fillets. If you buy cut pieces, look for moist, translucent flesh without browning or dryness at the edges, and ask when the catch came in.