Players will receive a fishing pouch to track and store Rare Fish.
Different fish are available based on the location being fished in:

All locations above ground will have different fish depending on whether the water is Fresh (pools, lakes & rivers) or Salty (oceans), and depending on the temperature (warm, cool or icy).
Some fish can only be found underground, with some only being able to be caught in locations below layer 0
Some fish can only be caught in one specific biome.
Some fish can only be caught within certain environmental conditions, such as weather, time of day and phase of the moon.
Some fish can only be caught in one specific location, such as at the server spawn.

The chance of a rare fish being hooked can be drastically improved with bait:
Rot Cakes, can be crafted with 5 rotten flesh and 4 bread
Worm Bait, can be found when harvesting mature wheat, carrot, beetroot and potato plants
Jellyfish Bait, drops from Titan Jellyfish

Right click with the bait to throw it into water. Bait effects last for 120 seconds each and can be stacked by throwing more bait in.

Take the elevator down to the Docks to see the Catch of the Day, collect them to earn Fishing Tokens. Fishing tokens also have a small chance to drop whenever catching rare fish. Fishing tokens can be spent on decorations, skins and more. The stock of the Fishing Token Shop can be increased by reaching certain Fishing Legacy levels.

Collecting all 5 rarities of a fish will increase the players Fishing Legacy (/fishlegacy). Fishing Legacy provides access to fishing related perks and titles:
Level 1 - Sea Pickle
Level 3 - Pond Dweller - Fish Pouch now shows Fish Locations
Level 5 - Kelp Enjoyer - Base Fishing Power increased by 1, Unlocks Lunar Bobber in the shop
Level 10 - Sushi Enthusiast - 2% chance to double your catch
Level 15 - Tuna Destroyer - Titan Jellyfish appear occasionally when fishing, kill them to get Jellyfish Bait, or a chance of a Lure 4 book
Level 20 - Crab Master - Base Fishing Power increased by 1, unlocks new stock in the token shop
Level 25 - Whale Lord - Black Titan Jellyfish have a small chance to spawn. Black Titan Jellyfish always drop a Lure 5 book
Level 30 - Lure Leviathan - Chance of double catch increased to 4%, unlocks new stock in the token shop

Hope you all enjoy this, it's been a long time coming, and a special thanks to @Baurd who helped to bring this to life.