You Need To Talk To Some Fisherman you can get one at Eterna City....
A Good Rod is available within Roue 209 in Diamond and Pearl.
same place as diamond and pearl.
Route 222
You can catch Lanturn in Pokémon Diamond and Pearl by Fishing with the Super Rod in Route 220.
You can obtain QUILFISH but fishing at Iron Island with a Super Rod.
you have to trade from diamond and pearl. in diamond and pearl you can find them on routes 219 and 221 with a super rod. you have a 5% chance of finding one there. Hope this helped!
Using the Super Rod nearby Valley Windworks. The Super Rod can be gotten from a fisher (not fishing) at the Northeast Island.
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To acquire the Good Rod in Pokémon Diamond, Pearl, and/or Platinum, simply travel to Route 209 and you will meet a fisherman who will give you the Good Rod.
You either use Pal Park or you can find it in Victory Road in the Water (Super Rod)
If it's on diamond, pearl, or platinum you use a good rod on the little island with the two tuber kids just south of Sandgem town
you get the good rod from a man at a dock near Solaceon town go south and hes on a dock.. Answer his questions say yes and he'll give you the good rod. Note: This for Diamond and Pearl