Fishing in Terraria is a useful activity that allows you to obtain ingredients for potions and gather valuable materials. It is often needed at higher difficulty levels. To start fishing, you'll first need to acquire bait.  

How to Acquire Bait for Fishing in Terraria

You can obtain bait through several methods.

Using a Bug Net

The easiest and most convenient method, allowing you to gather bait such as worms, maggots, hellgrammites, and more. Bug Nets come in three types: standard, golden, and lavaproof. The first can be purchased from a merchant for 25 silver coins, and with it, you can create a sufficient collection of bait and head to fish at lakes or oceans.

The Golden Bug Net works twice as fast and can also cut tall grass or vines. Its rarity level is light red, and it sells for 5 gold coins. You can obtain it as a quest reward from the angler, with a drop chance of 1.25%, and it might drop on your first try.

The Lavaproof Bug Net can be crafted using an Obsidian Workbench and 15 Hellstone Bars. It's faster than the golden and standard bug nets and is also sold for 5 gold coins. This net allows you to catch creatures from the Underworld, like the Hellbender, Hell Butterfly, and Magma Snail, which can be used for fishing in the underworld.

Jellyfish

If crafting a bug net seems challenging or finding the necessary ingredients is difficult, you can always catch jellyfish. There are three types: blue, pink, and green. You can catch them using fishing. 

Angler

The NPC who gives rewards for completing quests. The downside is randomness - you might get either the necessary loot or something useless. However, the angler's bait has a power level of 15% to 50%. To receive rewards, you need to complete quests. The more quests your character completes, the higher the rewards will be.

You will encounter the NPC over time. Usually, they will be floating on the ocean's surface or sleeping. You can interact with them without building a house, but it's risky, and your character might die. The angler also has a moderate amount of bait drops, increasing with each completed quest. After completing 249+ quests, the number will always be 7.