It is in Route 119
You can use a good rod or super rod to find carvanha on the route southwest from fortree city.
You can find Carvanha in Route 119, use your Super Rod. If you want Sharpedo (final form of Carvanha), you can find it near Mossdeep City, use your Super Rod.
CARVANHA evolves into SHARPEDO at level 30 (CATCH CARVANHA AT SPRING PATH AND GREAT MASRH)
a pokewalker route.
U fish on route 118 and 119
near the weather institute you go past the bridge and go down fish with a good rod or super rod super rod has 100% chance to catch a carvanha
pastoria gret marsh super rod
Carvanha evolves into Sharpedo at level 30.
Ruby, sapphire and emerald you can find a Pokemon called carvanha and sharpedo both of which are sharks.
You can only catch Pokemon from the original Kanto and Johto unless you link trade from one of the Hoenn games eg: Emerald, Ruby, or Sapphire to one of the Sinnoh games and then trade to Either HeartGold or SoulSilver.
To get Carvanha: Go to Pastoria Marsh Find some water in any of the 6 areas Use the super rod to fish There is a 35% chance that you will catch a Carvanha.