The Salmon of Knowledge (Irish: bradán feasa) is a creature figuring in the Fenian Cycle of Irish mythology. (It is sometimes identified with Fintan mac Bóchra, who was known as “The Wise” and was once transformed into a salmon.)
The Salmon story figures prominently in The Boyhood Deeds of Fionn, which recounts the early adventures of Fionn mac Cumhaill. According to the story, an ordinary salmon ate nine hazelnuts that fell into the Well of Wisdom (an Tobar Segais) from nine hazel trees that surrounded the well. By this act, the salmon gained all the world’s knowledge. The first person to eat of its flesh would in turn gain this knowledge.