Obtaining the Old Rod
The "Good Rod" and "Super Rod" will also catch higher-level Pokemon, which Feebas is not. To obtain an "Old Rod," travel to Dewford Town. Dewford Town is an island located to the southwest of the game's main landmass. Go south in Dewford Town to the gym and talk to the old man on the right side. He will give you an "Old Rod."
Fishing in Route 119
Leave Dewford Town and travel to Fortree City. Head east out of Fortree City and enter Route 119. Route 119 is a long route with a river running through its center. You will need a Pokemon that knows "Surf" as Feebas can be located anywhere in the waters of Route 119, not just on the shoreline.
Strategies
Route 119 has 400 different water squares, and Feebas will appear in only six of them at random. Chris Lefevre, author of the "Pokemon Ruby Feebas FAQ," recommends fishing in each square a minimum of five times before moving to the next one. Once you catch a Feebas with the "Old Rod," whittle its health down and capture it. Feebas is susceptible to electric attacks. If you accidentally kill Feebas, don't leave the square and try again. Feebas will respawn at a high rate.
Feebas Benefits
Physically, Feebas is a weak Pokemon that isn't suited well for battle. Players covet it for its rarity. Many players also catch Feebas to evolve it into Milotic. Milotic is stronger than Feebas and cannot be caught in the wild.