you cant.
You can catch him on Mt. Coronet (upper) B1F with the old rod.
You can't catch Milotic. Instead you have to catch a Febass and max out it's beauty and level it up. Febass can be caught either at the Quiet Cave Pokewalker route or in a lake somewhere but I forget.
use a good rod for a febass. and they are mostly in sapphire
quiet cave on pokewalker
its called febass and yes
It is in a certain body of water in Mt. Coronet. (Need Super Rod)
On route 222. If youre coming from lake valor its the third fisherman.
In Pokemon Black and White, Febass evolves when you trade it while it is holding a prism scale.
No. In Diamond/ Pearl there are four fishing spots, and you can only catch it with a Super rod. In Platinum you do not require the Super rod, but be able to catch it in the same four fishing spots.
Do you remember where the fog area in Mt Coronet is? If you fish there with the super rod you should find Feebas.
route 118