You’ve probably seen tips for buying fresh, whole fish: Look for clear eyes, shiny skin, red gills, and so on. But what if you’re buying fillets?  No eyes, no skin, no gills.  In that case, look for firm, tight flesh that bounces back readily when pressed with a fingertip.  Avoid fish that seems soggy or is bathed in milky liquid.  Also, steer clear of fish with a strong, fishy odor.  To thaw frozen fish without turning it to mush, thaw it in the refrigerator or under a thin stream of cool water—just until the point at which it starts to become flexible. Then, prepare it promptly!