Whether you're buying fresh water fish or an ocean fish, a flat fish or a round one, there are some common indicators of freshness:
• The eyes should be clear, bright, and slightly bulging. If they are cloudy or sunk into the fish's head, take a pass on that one.
• The gills should be bright red.
• The flesh should be firm and resistant. If your finger leaves an indention in the flesh, that means it's more than a day old.
• The scales should adhere tightly to the fish.
• The fish should smell like the sea - clean, fresh, and briny. Avoid fish that smell of ammonia or that smell overly "fishy."
• The fish should have a good overall appearance. This means no cuts or bruises, fins and tails are flexible, and the fish is moist.
If you buy your fish pre-cut into portions, it can be a bit harder to assess its freshness. In general, cut pieces of fish should be shiny and moist with no discoloration. It should still smell briny and ocean-like, and not "fishy."
As always, it helps to have a trusted fishmonger at your service!