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) The Gumblejack was considered one of the tastiest fish in Mutter's Spiral. (TV: The Two Doctors)

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

History of fish on Earth
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)

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!)

The Twelfth Doctor observed the "perfect defence" of a Pufferfish 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:

Elsewhere in the universe
Fish also existed on other planets throughout 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)

Fish also existed which were able to fly. The Eleventh Doctor observed sky fish and a sky shark in Sardicktown which swam through fog. (TV: A Christmas Carol)