Goldfish

Goldfish were a species of fish native to Earth; they were renowned for their short memory. The First Doctor stated he wasn't a goldfish when it was suggested he had forgotten the events of a mere moment ago. (DW: The Romans)

In Cardiff as part of Torchwood Three, Suzie Costello bought goldfish in bulk and began killing them to test the Resurrection gauntlet. (WEB: torchwood.org.uk)

The prison ship containing a Minotaur had a goldfish bowl. The Eleventh Doctor tried to save the goldfish from the Minotaur when it was attacking, but Gibbis simply ate the goldfish later. (DW: The God Complex)

In Series 6's special "Bad Night" the Doctor storms into the TARDIS with a bowl containing a goldfish while Amy foolishly answered the DOCTOR's phone. He pushes the bowl into Amy's hands and snatches the phone speaker away from her. He assures the Prince that his mother (Elizabeth?) is save aboard the TARDIS. Soon he recognizes that he stole the wrong fish and runs outside again yelling to River that they have only 3 hours left to save the Commonwealth since then the petshops will open again.