A shark was a type of predatory fish found in the oceans of the planet Earth.
The term "loan shark" was used during 20th century Earth to describe a person who offered money loans with extremely high interest, often belonging to a criminal organization. In 1944 of an alternate timeline, both Carmine and Sal worked as loan sharks. (ENT: "Storm Front", "Storm Front, Part II")
The 22nd century Military Assault Command Operations (MACO) organization featured a Mako shark on its Enterprise NX-01 mission patch. (ENT: "Countdown")
In 2376, a holographic version of Commander Chakotay referred to Lieutenant Reginald Barclay as a "shark" due to his skill in playing cards. (VOY: "Pathfinder")