Fishing.

[Tiberius Fireskull]

There are different types of fish that are deeper, which you can only access with an upgraded rod (unlocked at levels 5 and 15). These allow you to cast farther and sink your lure deeper. Also, there are a wider variety of fish in the ocean, so you should launch a fishing boat (unlockable at level 10) to catch those other ones.

[Mouseeye]

Ok! Thank you all very much! You, guys, answered all of my questions.