dying fish. In medieval times, seafood was less prestigious than other animal meats, and often seen as merely an alternative to meat on fast days. Still, seafood was the mainstay of many coastal populations. Kippers made from herring caught in the North Sea could be found in markets as far away as Constantinople. While large quantities of fish were eaten fresh, a large proportion was salted, dried, and, to a lesser extent, smoked. Stockfish, cod that was split down the middle, fixed to a pole and dried, was very common, though preparation could be time-consuming, and meant beating the dried fish with a mallet before soaking it in water. A wide range of mollusks including oysters, mussels and scallops were eaten by coastal and river-dwelling populations, and freshwater crayfish were seen as a desirable alternative to meat during fish days. Compared to meat, fish was much more expensive for inland populations, especially in Central Europe, and therefore not an option for most. Modern knowledge of the reproductive cycles of aquatic species has led to the development of hatcheries and improved techniques of fish farming and aquaculture. Better understanding of the hazards of eating raw and undercooked fish and shellfish has led to improved preservation methods and processing. Types of seafood The following table is based on the ISSCAAP classification (International Standard Statistical Classification of Aquatic Animals and Plants) used by the FAO for the purposes of collecting and compiling fishery statistics. The production figures have been extracted from the FAO FishStat database, and include both capture from wild fisheries and aquaculture production. Processing Fish is a highly perishable product: the "fishy" smell of dead fish is due to the breakdown of amino acids into biogenic amines and ammonia. Live food fish are often transported in tanks at high expense for an international market that prefers its seafood killed immediately before it is cooked. Delivery of live fish without water is also being explored. While some seafood restaurants keep live fish in aquaria for display purposes or for cultural beliefs, the majority of live fish are kept for dining customers. The live food fish trade in Hong Kong, for example, is estimated to have driven imports of live food fish to more than 15,000 tonnes in 2000. Worldwide sales that year were estimated at US$400 million, according to the World Resources Institute. If the cool chain has not been adhered to