Basic fish buying techniques are as follows: Avoid packages with signs of frost or ice crystals, which may mean the fish has been stored a long time or thawed and refrozen. Don't buy frozen seafood if its package is open, torn, or crushed on the edges. Avoid packages that are positioned above the frost line or top of the freezer case. A fish's eyes should be clear and bulge a little. Shrimp flesh should be translucent and shiny with little or no odor. Fish should smell fresh and mild, not fishy, sour, or ammonia-like. Some refrigerated seafood may have temperature indicators on their packaging, which show if the product has been stored at the proper temperature. Fish fillets should display with no discoloration, darkening or drying around the edges. The fish flesh should spring back when pressed. Whole mahi fish and fillets should have firm, shiny flesh and bright red gills free from milky slime. Frozen seafood can spoil if the fish thaws during transport and is left at warm temperatures for too long.