At some point i might widen the guide to other kinds of fish, atm it’s only about the Moby-Dick fish.
Where to Catch a Big Fish
Important side note
An additional effect to catching a big fish is, it won’t hunt you anymore on that planet.
Location of Big Fish Catch
You can catch the Moby-Dick fish on the third quest on Odysseum, the Harpie one, outside the Justice Valley dungeon.
Fished up heart of the abyss (200,000 coins) twice in Gaia.
If you wanted another location of another big fish
Last world near salt/crabs/monkey gravestones – Tigerfish