Fish

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

Fish on Earth
On Earth, fish swam in water. (TV: Listen) Oceans on Earth, including the Pacific, Indian and Atlantic contained deep ocean trenches. The high pressure in these trenches meant that fish had to be specially adapted in order to survive. (PROSE: Slow Decay) Land fish were able to travel across land. (TV: Kiss Kiss, Bang Bang)

Uses
On Earth, fish and chips were often served as food. (TV: The Rebel Flesh) The Eleventh Doctor particularly enjoyed fish fingers. (TV: The Eleventh Hour)

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

History
The Sixth Doctor ate fish, among other foods, at a feast with Alfred the Great in the 9th century. (PROSE: The Man Who Wouldn't Give Up)

In Victorian times, 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)

In the 1900s, when Fang Rock rock was engulfed in fog during a Rutan scouting mission, Leela found dead fish floating in a pool of water and poked them with her knife. The Fourth Doctor attributed their deaths to an electrical field present on the island. (TV: Horror of Fang Rock)

In 1984, Frank Harris was recruited from the refinery to work on a plan to restock the North Sea with fish. (PROSE: Downtime)

In 2011, due to an alien totem pole, fish started raining from the sky. (TV: The Curse of Clyde Langer)

In 2013, many fish in Ambermouth harbour died overnight due to the presence of silicon quartz in the water. Gulls gorged on the bodies until they couldn't fly. (AUDIO: Eldrad Must Die!)

When asked by Ramón Salamander's chef Griffin to tell him a menu for dinner, Victoria Waterfield suggested having fish on the menu. (TV: The Enemy of the World)

David Campbell caught a fish and teased Susan Foreman by dangling it in front of her face. (TV: The Dalek Invasion of Earth)

In 5000000023, Rose-the-Cat caught a fish on New Earth. (COMIC: A Rose by Any Other Name)

Undated events
The Second Doctor once ate fish served by Bior and his tribe in Scandinavia. (PROSE: That Which Went Away)

The Twelfth Doctor once observed the "perfect defence" of a puffer fish when questioning as to whether there could be such a thing as "perfect hiding". (TV: Listen)

Types of fish on Earth
Fish were common in Earth's seas, rivers and lakes. Types of fish included:

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Elsewhere in the universe
Like on Earth, fish could be found beneath the seas of other planets. Aaglon sharks were native to the waters of the planet Olleril. (PROSE: Tragedy Day) Fugora fish lived in the seas of Megerra. (PROSE: Mean Streets) Lake Abydos was home to singing fish. (AUDIO: Neverland) Yaddlefish were a type of fish which lived on Gallifrey. (PROSE: Blind Fury) Kandalinga was home to a wide variety of fish, including some which were larger than the TARDIS. (PROSE: The Fishmen of Kandalinga)

On the aqua planet, the First Doctor observed small fish swimming alongside larger Aquamonsters in patches of invisible liquid, making the illusion that they were in flight. (COMIC: Dr. Who on the Aqua Planet)

Similarily, in Sardicktown, fish existed which were able to swim through fog, making it appear as if they were flying. The Eleventh Doctor encountered numerous sky fish and a sky shark in the town. (TV: A Christmas Carol)

Universally, some fish could be eaten. The Gumblejack was considered one of the tastiest fish in Mutter's Spiral. (TV: The Two Doctors)

The Sevateem used spears to catch fish on their planet. (AUDIO: The Fate of Krelos)