Fish sauce are made with anchovies, mackerel, scabbard fish and salt. The bigger the fish, the more mercury you might expect, especially if predator fish like scabbard fish. They do not have any additives like sugar, hydrolyzed protein, or preservatives. Vietnamese prefer sauces without a strong smell, and transparent with a deep golden amber color. "First press" fish sauce, meaning the sauce is bottled from the first time the fermenting barrels are drained, also indicates quality. Lastly, when measuring the nitrogen level of fish sauces (N), most fish sauce on the market falls within the mid 20N range. Anything over 30N is
Fish sauce "kecap" in Indonesia might be the precursor of ketchup. By 50–100 BC, demand for fish pastes in China had fallen drastically, with fermented bean products having become a major trade commodity. Fish sauce, however, developed massive popularity in Southeast Asia. Food scholars traditionally divide East Asia into two distinct condiment regions, separated by a bean-fish divide: Southeast Asia, mainly using fermented fish (Vietnam, Thailand, Cambodia) and Northeast Asia, using mainly fermented beans (China, Korea, Japan). Fish sauce re-entered China in the 17th and 18th centuries, brought from Vietnam and Cambodia by Chinese traders up the coast of the southern provinces