As of the latest patch they collect pearls when you bite them.

P. E. A. R. L. S. That's all you need to know about this amazing creature.

The tek cave update gave the anglers the ability to gather pears, according to the wiki

If you build a base on the rock island in the lake in aberration or the big lake near the surface entrance breed an army of fully mutated anglers, mantas, and eels and set them on wander and aggressive and your lakes will be karkinos and spino free

- Main use is after tamed they will attract more anglers which can be harvest for gel
- Secondary use would be a mobile underwater tame that also has a built in light
- Lastly they can be harvested for gel which tames Manta's

(Angeler gel is the longest burning fuel source at 6 min per gel)