Daing, tuyô, or bilad are dried fish from the Philippines. Fish prepared as daing are usually split open, gutted, salted liberally, and then sun and air-dried. There are also "boneless" versions which fillets the fish before the drying process. It was originally a preservation technique, as salt inhibits the growth of bacteria, allowing fish to be stored for long periods of time.
Daing
Daing being dried
Various types of daing sold at a store in Pangasinan
Daing na pusit (squid daing) with sea grapes
Fresh fish rapidly deteriorates unless some way can be found to preserve it. Drying is a method of food preservation that works by removing water from the food, which inhibits the growth of microorganisms. Open air drying using sun and wind has been practiced since ancient times to preserve food. Water is usually removed by evaporation but, in the case of freeze-drying, food is first frozen and then the water is removed by sublimation. Bacteria, yeasts and molds need the water in the food to grow, and drying effectively prevents them from surviving in the food.
Fish barn with fish drying in the sun – Van Gogh 1882
A fish flake, such as this one in Norway, is a rack used for drying cod
Flattened fish drying in the sun in Madagascar
Assorted dried fish in Imphal, Manipur, India