Pa's Fishing Aid

 is a unique version of double-barrel shotgun added to Fallout 3 with the Point Lookout add-on, but was essentially cut post-production.

Characteristics
It looks identical to its regular version, the double-barrel shotgun, but differs in damage, price and other characteristics. It can only be repaired with combat shotguns.

Location
The weapon is cut from the game and can only be acquired through the console.

Behind the scenes

 * The name is most likely a reference to the commonly known idiom "shooting fish in a barrel" or a method of fishing known as "shotgun fishing" - in which a fisherman simply fires a large rifle or shotgun into a pond, using the shock-waves to kill fish.