Fishing

At the start of the game you are given a So-So Old Rod to fish up your first Magikarp. Periodically you will be required to return to the Fishing Pond to fish up new Magikarp as yours retire somehow. Every time you return for a new Karp Mayor Karp will give you some Exp.

New Gen Exp.
There are several ways your Magikarp can be retired. There are probably other methods that have not yet been discovered, be vigilant.
 * Taken by Pidgeotto (Event No. 5) (Event No. 41)
 * Blown up by Voltorb (Event No. 3)
 * Accidentally Evolved (Event No. 25)
 * Max Level
 * Forced Retirement (available at some point)

Fishing Rods
There are multiple types of fishing rods, as you beat more and more leagues Mayor Karp improves the rod you are able to fish with, the quality of the rod determines what patterns of Magikarp are obtainable and how likely they are. You can also fish up Dratini, no you don't get to keep it. Fishing a Dratini gives you a Skill Restore Item, and is a unique Event. Dratini may only be fished up once.

Additionally if you use a Rod that is facing the opposite direction of the other 2 it will fish up a Ditto Magikarp, this is a unique Event and unlocks the Ditto Cushion in the Diamond Store. This Event can only happen once