Neptunium is a new material provided by the Aquaculture 2 mod. It can be used to create some new Armor, Tools and Weapons. Although if you’re using a mod like Just Enough Items, you might notice that no recipe for Neptunium is provided.
How to get Neptunium
As Neptunium doesn’t have a recipe, it can only be obtained as a random drop from fishing. When casting out your rod, you’ll have a chance of obtaining the ‘Neptune’s Bounty’ treasure box.

The chance of receiving a Neptune’s Bounty is increased if you’re using the Luck of the Sea Enchantment on your Fishing Rod. You can also try using Gold Hooks, which gives increased Luck.
When you find a Neptune’s Bounty, place it down in the world and open it like a Chest. Inside, you have a chance of finding some Neptunium Ingots. This is currently the only way to get Neptunium in Minecraft. It can then be turned into different Armor and Tools, which give unique effects, and you can find out more below.
Neptunium Armor
Wearing Neptunium Armor will make surviving underwater a lot easier. With a full set, you should be able to survive indefinitely, without needing to think about lighting or breathing.
Wearing a Neptunium Helmet will provide players with the Night Vision effect when underwater, making visibility much better. Whereas the Neptunium Chestplate will allow players to breathe underwater indefinitely, removing the need for Potions of Water Breathing.

Neptunium Leggings will cause the player to fall underwater. And Neptunium Boots will allow players to swim faster when underwater. Using Neptunium Ingots, you can create each Armor item like you would from any other material.
Neptunium Tools
Likewise, an assortment of Neptunium Tools & Weapons can be created. These also provide some bonus effects when used underwater, and will definitely help you survive for longer beneath the surface.

When using a Neptunium Pickaxe or Shovel, there’ll be no penalty when it comes to the speed of breaking blocks. Whereas Swords and Axes will deal bonus damage to targets when used underwater. If you use a Bow instead, then the trajectory of Arrows aren’t impacted by water. Finally, land that is Hoed will always be hydrated.
Notes
It’s worth noting that Neptunium items can be placed in a Blasting Furnace, allowing you to recycle them. You’ll receive Neptunium Ingots in return. Neptunium can also be turned into Neptunium Blocks and Nuggets, like with other materials.