Fish

Fish were a variety of water-dwelling animal found on Earth and many other planets.

Uses
On Earth, fish were often served with chips as food. (TV: The Rebel Flesh)

Fishing, the sport of catching fish, was a popular pastime enjoyed by the Doctor. (TV: The Androids of Tara, The Two Doctors)

History
Whilst dressed as Sherlock Holmes, the Eleventh Doctor asked one of Walter Simeon's servants if he had a fish called Colin. When he said 'no', the Doctor said he didn't think he had. Also Clara Oswald, while serving as a governess under the alias Miss Montegue, claimed to her young charges in 1892 that she invented fish so she wouldn't be alone while swimming. (TV: The Snowmen)

Victorian showmen used to draw the crowds by taking the skull of a cat, glueing it to a fish and calling it a mermaid. The Ninth Doctor compared the Slitheen's Space Pig with this trick while explaining the Space Pig's true nature to Toshiko Sato. (TV: Aliens of London)

Due to an Alien Totem Pole, fish started raining from the sky. (TV: The Curse of Clyde Langer)

Related Species
Some intelligent species seemed to be descended from fish or were at least fish-like in appearance. Example of this were the Aridians, (TV: The Chase) the Fishmen, the Pescatons, (AUDIO: Doctor Who and the Pescatons) the Ockorans, the Kalarians, the Saturnyns, (TV: The Vampires of Venice) the Dax, the Hath (TV: The Doctor's Daughter) and Zargath's race. Damon converted humans into fish people through surgery. (TV: The Underwater Menace)

Examples of non-sentient fish included pilot fish, singing fish, Aaglon sharks, fugora fish, sky fish, and Gumblejack. (TV: The Christmas Invasion, AUDIO: Neverland, PROSE: Tragedy Day, PROSE: Mean Streets, TV: A Christmas Carol, The Two Doctors)