For 10 points, name these fish, one of which contained all the world's knowledge.
In the tale of Culhwch (KILL-hookh) and Olwen, Arthur and his men go to one of these creatures, described as the oldest of all animals, to inquire about the location of Mabon ap Modron. That enormous example of these creatures then carries two of Arthur's men to Mabon's prison. Before becoming a type of bird, a being lived as one of these creatures for a year in Fintan's Grave. According to the Poetic Edda, Loki takes this form immediately before being bound by the Aesir. Another one of these animals once ate nine hazelnuts, causing it to become endowed with supernatural powers before being cooked and eaten by Finn MacCool. For 10 points, name these fish, one of which contained all the world's knowledge.
In the tale of Culhwch (KILL-hookh) and Olwen, Arthur and his men go to one of these creatures, described as the oldest of all animals, to inquire about the location of Mabon ap Modron.
salmon [prompt on fish] &lt;Thompson&gt;