The first time I ate a whole fish was in Spain. I was fulfilling stereotypes that Europeans have of American female college students by refusing to eat meat (fast forward seven years later, and I'm making pancetta- who would have thought?). I spent time getting "immersed" in the Spanish language, living in the apartment of a young woman in Leon. She wasn't freaked out by eating habits, and she made me delicious pork-free meals, which can be quite a tall order in Spain.
One evening she plopped down an entire cooked fish in front of me for dinner. Apparently it was trout season, and they had just been caught in the river. By the look on my face, she could tell I had never eaten a whole fish before. She showed me how to slice through the flesh at the base of the head and near the tail and easily remove the fillets from the spine. It ended up being some of the best fish I've ever had in my life. The flesh was rich, moist, and flavorful. Almost like salmon without even a hint of fishiness.
Now I always prefer to cook fish whole. It's harder to overcook and dry out whole fish because the skin and the bones keep all of the juices and flavors sealed into the meat. It's also easier to select a fresh fish if it's left whole. Many people are scared to cook fish, relying on professionals in restaurants to make it for them, but baking or grilling a whole fish is one of the simplest and fastest meals to make. After lots of trial and error, here are my best tips for purchasing fish:
1. Stick to locally caught fish if possible. I've had some outstanding snappers in New Orleans, but I've never tracked down a great one in New York where I stuck mainly to porgies and sea bass. Astoundingly, branzino is all trendy in New York right now, but I don't understand why since its essentially a Mediterranean sea bass. No sea bass shipped in from Greece is going to taste better than something freshly caught in Montauk. Fish deteriorates rapidly while being transported long distances. Of course, this is just a guideline. I've purchased some fantastic fresh sardines from Portugal, and Whole Foods consistently carries high quality rainbow trout farm raised in Idaho.
2. Look into its eye. Most people seem to know that the fish's eye should be clear, not cloudy.
3. Check the gills. This is my favorite tip. In seafood or ethnic markets, the fishmonger will often happily let you peel back the gills and examine them. Freshly caught fish will have deep red, almost purple gills.
4. Poke the fish. In legit seafood markets, the fishmongers will also let you poke the fish to see if the flesh bounces back. It is a bad sign if your finger leaves an indentation; it means the fish is mushy and not fresh. I obnoxiously complained once in a cooking class about a certain upscale food market preventing customers from touching the fish, and my classmate cried out, "but they don't want people contaminating it!" I think it should always be ok to touch it unless some customers intend to eat it raw.
5. Examine the skin. Fresh fish is usually shiny, not dull.
6. Smell the fish. This is another common tip, but I find it tricky. It's true that fresh fish doesn't smell "fishy" at all, but even in the cleanest seafood store, there is usually a strong enough fish stench to prevent you from really smelling what you're buying. Sometimes I've brought things home, and then realized that I'd made a big mistake after opening the package.
Fish fillets are something different altogether, and I usually steer clear of them because they are more difficult to judge for quality and freshness. If I need a fillet, I prefer to fillet a whole fish at home. I have a sneaking suspicion that many markets turn their whole fish into fillets as a method of pushing product when it's past its prime. That said, I have had some success buying fish fillets by using common sense like sticking to locally caught fish when buying fresh and buying flash frozen fillets of things like wild Alaskan salmon. I also make sure that the flesh looks dense, and that it's still translucent and not opaque. After that, buying good fillets can be a bit of a game of chance, and that's why I almost always stick to whole fish.