A better rod lets you catch better Pokemon. This guide on Where To Find The Good Rod In Pokemon Brilliant Diamond And Shining Pearl will tell you where you can find the upgraded fishing rod as the old rod you get earlier in the game doesn’t let you catch a lot of the Water Pokemon you can find.
The Good Rod is available relatively early in the game but you will still need to progress some ways before you can get it. After you beat the 2nd Gym Leader and obtain your second badge, you will need to clear out Team Galactic’s building in the same town so that you can unlock your bike. Once you have your bike the story will tell you to head to Hearthome City. Once there you will need to do a few bits and pieces, finding the Contest Hall and then battling your rival as you try to leave the town. Once your rival has been defeated, you need to head to Route 209
Where To Find The Good Rod In Pokemon Brilliant Diamond And Shining Pearl
Route 209 is on the way to Solaceon Town. Partway down the route you will encounter a group of fisherman fishing from some wooden platforms in the water. Speak to the fisherman shown at the image at the top of this post. When you speak with him tell him that you enjoy fishing.
After a few comments he will agree to give you the Good Rod. Now you can use that to catch higher level water Pokmeon.
in Pokemon Brilliant Diamond And Shining Pearl Guides