A trident is a three-pronged spear. It is used for spear fishing and historically as a polearm.
Trident of Poseidon
Illustration of a trident user from the Wubei Zhi, late 16th to early 17th century
Fountain of Neptune in Diafáni, Karpathos island
Dutch fishermen using tridents in the 17th century.
Spearfishing is fishing using handheld elongated, sharp-pointed tools such as a spear, gig, or harpoon, to impale the fish in the body. It was one of the earliest fishing techniques used by mankind, and has been deployed in artisanal fishing throughout the world for millennia. Early civilizations were familiar with the custom of spearing fish from rivers and streams using sharpened sticks.
Spearfisher Monument in Croatia
Fisherman with a spear in a wall painting from the tomb of Usheret in Thebes, 18 Dynasty, around 1430 BC
Poseidon/Neptune sculpture in Copenhagen Port
Mosaic, 4th century BC, showing a retiarius or "net fighter", with a trident and cast net, fighting a secutor.