Dictionary of Ichthyology  

John Dory = Zeus faber, a fish having an oval spot on each side, reputedly the fingermarks of St. Peter left when he picked up the fish to take the coin from its mouth. Haddock (Melanogrammus aeglefinus) also have these spots and are also said to be the fish St. Peter picked up. Since neither species is a freshwater one, this is ichthyogeographically untenable.
Fauna Illustrations by William MacGillivray from Wikimedia Commons: http://commons.wikimedia.org/wiki/File:

           Canadian Museum of Nature