underwater routes 124-126,but rare.
no you do not have to catch a relicanth to get a rayquaza
You can catch it when you use dive.
No only in ruby and sapphire and emerald.
To catch relicanth use Hypnosis by Gengar and get lots of Dive Balls
You can't catch Relicanth. You have to trade from Ruby, Emerald, Sapphire or any other game that has him captured.
no you do not just the Pokemon relicanth and wailord.
erwater cavern surrounding sootopolis city
relicanth
You can see and catch Relicanth under the water just outside Sootopilis(spl?) City, in the mossy grass.
Relicanth can be found in the seaweed underwater just outside of Sootopolis City.
Relicanth are very rare, but you can find them on underwater routes 124 and 126.
Nothing evolves into Relicanth in Pokémon Emerald.