The term 'fresh' in the seafood industry implies that the fish has never been frozen, from catch to market to consumer. It has been kept in a chilled state until it ends up with the final consumer, you. In reality, the term Fresh should equate with Quality. Certainly a fish just caught and consumed that same day would be very high in quality if caught from the right waters. Now, if that fish were to set in the refrigerator for 9-12 days, would you still consider that it had the same high quality as the first day it was caught? People will, and should, ask the seafood seller when they received the fish they are considering purchasing but I have yet to hear someone ask a question equally, if not more important.... When and Where was the fish caught? If you ask that question and they can't answer it, go elsewhere.

The California Sea Grant program, a cooperative extension of the University of California offers these consumer tips for purchasing high quality seafood:

Consumers should base their seafood purchases on quality. Frozen seafood can be superior in quality to fresh products. Many fish and shellfish are "flash frozen" within hours of harvest. It might take several days for the same seafood to make it to your local seafood dealer as "fresh".

With recent technological advances, fishing fleets are able to clean and flash-freeze fish virtually moments after they are caught. Flash-freezing, a process used for Frozen at Sea (F.A.S.) fish, instantly, in as little as 3 seconds, freezes the water inside fish tissues, thus preserving juices and maximizing flavor and texture when cooked. Modern fishing trawlers have become virtual fishing factories at sea. The seafood they harvest is cleaned, processed and flash frozen (minimum temperature of -40°F) aboard ship within 2 hours of catch. Quality and freshness are maintained because the seafood is packed and shipped frozen, held in sub-zero freezers, and never thawed until you use it. The seafood is kept in optimum condition during its trip to distributors. There is never a need to ask the questions you would ask about "fresh" seafood: how long it traveled to distributors, whether it was kept cold enough in route to maintain its flavor and safety, or how long it has been on ice.

Roger Fitzgerald, editor of Seafood Leader, a leading industry magazine, puts it like this: "A fish that's good - unspoiled - is one that looks, tastes and smells like it just came out of the water. The issue isn't whether a fish is frozen or fresh, but whether it's spoiled or unspoiled."

It has been noted that these flash-frozen fish may, in fact, be in better shape than fish that sat out in a hold at sea for days before being sold as fresh. Some fishing boats are out at sea several days at a time and the fish are sitting on ice all this time. So, indeed some fish can be up to 3 days old before they are even brought to the seafood processing plant. There is even a term when the boat returns to dock, 'fresh on top'. 'Fresh on top' are fish from the last catch and therefore fresher than the fish at the bottom of the pile from the first catch. Interestingly, in a blind taste test of F.A.S. (Frozen At Sea) salmon hosted by Chefs Collaborative, F.A.S. Alaskan Coho ranked first on flavor, texture and aroma, beating out both fresh Oregon chinook, wild and hatchery.

To determine if a fish has been properly frozen, as with fresh fish check its appearance: it should be somewhat shiny and have no white freezer-burn spots. It should be hard as a rock, showing no evidence of previous defrosting.

And always remember food safety :

Check fresh fish carefully before buying (bruised or brown spots indicate decomposition, which may mean that bacteria are present), or buy fish that was frozen immediately after it was caught and stored frozen before it came to the market.

Cook fish and shellfish thoroughly. Handle raw fish as you would handle other raw meat products; take care not to contaminate cooked food or vegetables with the utensils used to cook raw fish, and wash utensils and hands thoroughly in between handling.

Sources
1.) "America's fish: fair or foul?" Consumer Reports, February 2001.
2.) University of California, the United States Department of Agriculture, and the United States Department of Commerce cooperating
3.) Alaska Sea Grant Marine Advisory Program, John P Doyle
4.) The Complete Guide to Buying and Cooking Fish, Bittman, Mark (Macmillan, 1994).