Fishing is completely custom some notable drops from fishing are: Seashells (Contains sea food items and Pearl gemstones), alchemy materials, currency, and general mc items. (Enchantment books, Armor, etc are not available in the fishing droptable) 

Droptable: Ink Sac, Glowing Ink Sac, Raw Cod, Raw Salmon, Lily Pad, Seagrass, Kelp, Copper Coin, Silver Coin, Fishing Rod, Name Tag, Slimeball, Prismarine Shard, Sea Pickle, Waxed String, Seashell, Sea Serpent, Rare Fish Scale 

Required Tool: Iron Pickaxe
Blocks: Coral Blocks (not the fans etc)

Swim deep into the waters anf harvest the coral blocks for loot.

Droptable: Sand, Red Sand, Large Shell, Arrow, Gold Nugget, Bone, Seashell, Spice Plant, Glowberries, Iron Nugget, Prismarine Shard, Raw Salmon, Raw Cod, Ink Sac, Shroomlight, Moss Block, Moss Carpet, Raw Copper, Candle, Small Dripleaf, Big Dripleaf, Sea Pickle