FishPing is not an addon. It works by replacing WoW sound files.
How to install:
Copy the "Data" folder inside FishPing to your "World of Warcraft" directory so that it forms:
/World of Warcraft/Data/Sound/Spells/FishingBobber_ver2_1.ogg
Yes, this is all just a revival of the classic "FishPing" addon that stopped working as of 4.3.3 because the client now expects ".ogg" files rather than ".wav" files.