A scaly, cold-blooded vertebrate that lives wholly in water, typically having gills and fins.
Season 1, Episode 4 - The Luminous Fish Effect
Aired October 15, 2007
When Sheldon is fired, his life descends into a series of bizarre obsessions, including "fixing" eggs and weaving ponchos. A concerned Leonard decides there's only one person who can bring Sheldon back from the brink: his mother.
Season 2, Episode 1 - The Bad Fish Paradigm
Aired September 22, 2008
When her first date with Leonard doesn't go to plan, Penny finds an unwilling confidant in Sheldon. Sheldon can not handle the stress of keeping Penny's secret, so he decides to move out of the apartment.
Season 6, Episode 10 - The Fish Guts Displacement
Aired December 6, 2012
When Amy comes down with the flu, she calls on Sheldon to take care of her. After Amy enjoys Sheldon's care a little too much, she takes advantage of him as she gets better. Meanwhile, Bernadette tells Howard to join his father-in-law, Mike, for a fishing trip to get to know him better.