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.
Carvanha is not a legendary Pokémon.
Sharpedo
According to the national dex, Pokemon 318 is Carvanha.
leveln50
It is in Route 119
Carvanha is a Water and Dark type pokemon.
Carvanha is not a legendary Pokémon.
Carvanha evolves at level 30.
A Carvanha evolves into Sharpedo at Level 30.
Sharpedo
idalia
Carvanha is #318 in the national pokedex, and it is a Water-Dark type Pokemon.
According to the national dex, Pokemon 318 is Carvanha.
leveln50
It is in Route 119
a pokewalker route.
Fish near the Village Bridge.