Shark

A shark was a type of predatory cartilaginous fish. Sharks were native to Earth, with various shark-like creatures existing elsewhere as well.

Earth Sharks
In Atlantis, the Second Doctor, Ben, Polly and Jamie were nearly fed to sharks as a sacrifice to Amdo. (DW: The Underwater Menace)

In the 1970s, the Australian branch of UNIT discovered a fragment of Brokk's spaceship in the belly of a shark. (MA: The Eye of the Giant)

Samantha Jones was afraid of sharks after watching the film Jaws 2. (EDA: The Taint)

Sharks of Other Planets
&nbsp
 * On an unnamed planet, the First Doctor, John and Gillian helped a race of intelligent frogs catch a shark which was trying to eat them. (TVC: Shark Bait)
 * Aaglon sharks were creatures native to Olleril. (NA: Tragedy Day)
 * The Pescatons apparently evolved from sharks or a shark-like species. (BBCR: Doctor Who and the Pescatons)
 * The planet Philjax III was home to a species reminiscent of sharks. (DWBIT: #9)
 * The Empetniks were a shark-like species native to the planet Senkus Sha. (DWBIT: #27)
 * On the planet where Sardicktown was found, there were flying sharks which lived in the crystalline fog. (DW: A Christmas Carol)
 * In the 23rd century, a giant armoured shark called a Zaralok was transported to Earth and attacked the aquatic research station Poseidon 8, before it was sent back by the Eleventh Doctor and Amy Pond. (VG: Shadows of the Vashta Nerada)

Other References

 * The Ockorans designed their suits and named their soldiers (Selachians) after sharks to intimidate their enemies. (PDA: The Murder Game, The Final Sanction)
 * The Roboforms and Sycorax were compared to pilot fish and sharks, respectively, with the Roboforms preceding the more powerful Sycorax. (DW: The Christmas Invasion)