Prismite

Prismites are a type of Hardmode fish which are found rarely by fishing in the Hallow in any layer. They are used to craft Seafood Dinners(Desktop, Console and Mobile versions) and Lifeforce Potions.

Crafting

Result	Ingredients	Crafting station
Seafood Dinner(Desktop, Console and Mobile versions)	Prismite2	Cooking Pot or Cauldron
Lifeforce Potion	Bottled Water Prismite Moonglow Shiverthorn(Desktop, Console, Old-gen console and Mobile versions) Waterleaf	Placed Bottle or Alchemy Table(Desktop, Console and Mobile versions)

The best way to fish for Prismites is to fish in a forest Hallow in the surface or sky. This gets rid of the chance to fish up any other item, like underground or biome-specific fish and loot. Although, fishing in this way prevents you from fishing for a combination of important potion fish.
It is advisable to use Prismites solely for crafting Lifeforce Potions, because of their immense value to players. Seafood Dinners can also be crafted with other common catches like Princess Fish, which are even caught from the same fishing pool.
As with other Hallow-exclusive content, Prismites can be acquired prior to entering Hardmode if an artificial Hallow is created, e.g. by bringing in Hallowed Seeds from a Hardmode world, or if playing in a Celebrationmk10(Desktop, Console and Mobile versions) world.
3DS Prismites have no use apart from being sold (1 GC each), as neither Seafood Dinner nor Shiverthorn is present.