The GameShark code for getting Feebas in Pokemon Ruby, Sapphire and Emerald is 11E58406 0C731B08. This code does not automatically give the player Feebas, but it does make this hard-to-find Pokemon easier to locate. This GameShark code makes Feebas appear in every tile that the player fishes from along route 119.
Without the help of a GameShark cheating device, it is still possible to catch Feebas. This Pokemon is hard to catch because it appears only in a select area of the game. Along route 119, there are 1 to 6 tiles on which Feebas appears. He is the only Pokemon that appears on these tiles, but locating the position of the tiles is difficult because they are randomly selected when the player begins a new game. Thus, the tiles that produce Feebas during one game do not produce him in a newly started game.
When trying to catch Feebas normally, it does not matter what tile the player is standing on but the tile from which they are fishing. This is important because the player has the ability to fish from two tiles while standing on a corner tile. It was originally believed that the tile on which the player was standing was the tile that determined what they caught.