Prahok contains fermented fish, and traditional Khmer use a small fish called Trey Riel to produce it. The importance of prahok and the fish is very much alive in the name of the Cambodian currency: Riel. Prahok was once important in the everyday life of Cambodians, that people from the inner land travel to places to buy Riel-Fish at the markets. It became kind of a currency and was sold for certain amounts of rice.
In full here.