Many Irish Holy Wells had a sacred "Trout of Knowledge" that had obtained wisdom through eating the hazel nuts that had fallen in from the tree above.

Finn McCool got his prophetic thumb from cooking a sacred trout for someone else and touching it. He could suck his thumb and see the future. He used to live his life by what his thumb told him would happen - I think this is where the Rule of Thumb comes from.

Many an Irish child, spirited way by the Gentry were turned into trout.

One Irish monk turned into an albino trout.

There's a whole load of old trout in Irish lore.