Salted fish had its origins in Asia as a "poor man's food". In the early days when there was no such thing as refrigeration, people living by the sea with a plentiful supply of fish would salt and dry the leftover fishes in the sun to preserve them. A little bit of salted fish can go a long way for an Asian family as it can be mixed with porridge for a tasty meal. Times have changed though, and salted fish is viewed in Chinese cuisine as an ingredient that enhances the flavour of many dishes ranging for bean sprouts to fried rice and claypot dishes. Salted fish is not just popular with the Chinese in Asia, but is very popular in Portugal as well.
The Portuguese tried to use the method of drying and salting on several varieties of fish from their waters, but the ideal fish came from much further north -- the cod fish. This is probably because of the intense flavour that comes from the natural oils of the cod fish. Called "bacalao", it caught on quickly among the Roman Catholic community because of the many days (Fridays, Lent, and other festivals) on which the Church forbade the eating of meat. This photo here is a dish of "bacalao" that I tried when I was in Portugal. It was very different from the dry, extremely salty type of salted fish that I am used to. In fact, it tasted more like a dish of cod that was soaked in brine!