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.
use a good rod for a febass. and they are mostly in sapphire
you cant.
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.
You can catch him on Mt. Coronet (upper) B1F with the old rod.
you catch it where mt cornet use rockclimb and there is a magby
You can catch it in mt. cornet, it changes its location in mt. cornet by day so try your luck at each bed of water
Spear Pillar mount cornet!
in mount cornet with honey
top of mt cornet
in the other dimension on top of mt cornet
Oh, Feebas, Hard one. You must go to cornet and get to the lowest part of the mountain. There, you will find a lake(ish) body of water. you must surf and fish in every spot. Every day there will be 4 spots where there are four feebas (one in each). Remember, each spot changes every day! ~bellafuzz
in mount cornet with a good rod