Since version 1.10 of Minecraft, fishing rods have had the ability to retrieve dropped items, which players can then pick up. However, fishing rods are still unable to pull in shot arrows and tridents, despite the fact that players can manually pick up these as well. This issue is related to MC-113818, MC-200476, and MC-137074.

steps to reproduce

1. Fire an arrow or a trident
2. Attempt to snag it using a fishing rod

Observed: It is not possible to hook the arrow or trident with a fishing rod.
Expected: You should be able to hook the arrow or trident with a fishing rod.

Note: It appears that fishing rods can hook any entity that can be targeted by the player except ender dragons, in addition to dropped items.