Comparing with 7.0 Artifacts for all classes, the unique Artifact: Underlight Angler has belonged to Fishing profession.
It requires Level 800 fishing and achievement: Bigger Fish to Fry which will catch all 18 rare fish in Legion to get the Underlight Angler.
Fishing 800 is easy to gain by catching the 18 rare fish. You can also free the rare fish to gain 5 points of fishing skill. Say you can acquire Underlight Angler when finished all achievements of rare fish on The Broken Isles.
There are three rare fish per zone, totally 5 zones including the zone-unspecific "ocean," so 18 rare fish are required. Rare lures will greatly increase the rate to catch rare fish, while Arcane Lures will gain a 10-min-BUFF to promote the rate of fishing the rare lures on The Broken Isles. This method reduced the difficulty of catching 18 rare fish. And the Arcane Lures can be purchased with Drowned Mana from Conjurer Margoss on a floating island just outside of Dalaran. 
Once you get fishing to 800 and complete the Bigger Fish to Fry achievement, you can fish up a Luminous Pearl to start the corresponding quest chain, then to obtain the fishing Artifact. Also, you need to level up your Artifact by clicking on the floating Luminous Pearl at the Dalaran fountain. Make sure to have your fishing pole equipped when looting rare fish, then release them will no longer reward fishing points but Artifact Power, every rare fish will offer 50 Artifact Power. Totally 23 levels similar to class Artifact Traits. Unlocking Artifact Trait tree, you will be given some special effects such as transmit to the nearest fish spot, Walk on Water, Breathe underwater, loot Blood of Sargeras, and other skills. 
Such a simple and practical fishing Artifact, get it now!