Sandlance sauce is one of the most commonly used fish sauces in Korea for a variety of reasons. 
It holds deep aromas of the sea and has a distinct flavour that transforms into flavourful umami when used as an ingredient. 
They are made by fermenting large amounts of sandlances in natural sea salt, extracting only the core extract of the fish. 
Fish sauce is a crucial ingredient in making traditional kimchi, which is not authentically vegan.

It can also be used to make a variety of other Korean dishes including, but not limited to, bulgogi, galbi, namool, kimchi soup, and more.