Shrimp and prawns are the most commonly available shellfish in the world. Their predominance stems from their delicious flavor, conveniently small size, rapid reproduction in the wild and in aquaculture, and the tolerance of their flesh to freezing. The two terms are often used for the very same animals; in the United States, “prawn” usually means a larger variety of shrimp. There are some 300 species of shrimp and close relatives exploited for food around the world, but the most common belong to one semitropical and tropical genus, Penaeus. Species of Penaeus can mature in a year or less and grow as long as 9 in/24 cm. Temperate-water shrimp belong to a slower-growing group and are usually smaller (a maximum of 6 in/15 cm). Today about a third of world production is cultivated, mainly in Asia.