Scrooge and the Magic Fish is Volume 12 of the Walt Disney Fun-to-Read Library. It is an adaptation of the story of the fisherman and his wife, with Scrooge McDuck in the role of both the fisherman and his wife.
Donald demands a raise from Scrooge, but Scrooge refuses, saying that he feels he is only a poor old duck and thinks his Money Bin is half-empty. Feeling down about this, Scrooge goes to the Millionaires Club, where he sees a sign for a fishing contest and decides to enter. He very soon catches a very big fish who suddenly begs to be thrown back into the sea, saying he will grant Scrooge's dearest wish if he does so. Scrooge, realizing this opportunity, wishes to have his Money Bin filled to the very top and lets the fish go.
Upon returning and seeing his bin filled with money all the way up to the ceiling, Scrooge decides maybe he was too hasty with his wish. He goes back out to sea and finds the fish again, and this time wishes he had a palace. The fish reluctantly has Scrooge's mansion transformed into one. Scrooge at first enjoys his new palace for half an hour, but he then gets even greedier and decides he should also be a king. Despite Donald warning him about how ridiculous he's being, Scrooge heads back to the sea and tells the fish that he wants to be a king, so the fish reluctantly grants that too. Scrooge returns to his palace to find many servants catering to his needs, a throne, and a crown to put on his head.
Scrooge then orders Donald to go tell the other Millionaires' Club members to come to the palace so he can see their envious reactions. But Donald scoffs at this, saying they'll more likely laugh at it. Scrooge decides that perhaps he should just wish to be emperor of the world, so he goes out to find the magic fish again, in spite of the weather turning sour. Scrooge tells the fish that he wants to be an emperor, but the fish has by now had it with Scrooge's greed and, as a result, undoes all the effects of Scrooge's earlier wishes, changing everything back to their original states.
When Scrooge returns to the Money Bin and sees it back to how it was at the beginning of the story, he is at first devastated to have lost everything he had gotten from the wishes. After a while, though, he remembers the lesson he has learned - to be content with what he already has - and then takes Donald out to dinner (though he still makes Donald pay for it).