From Team Fortress Wiki
The 'Fish' is a promotional item that is a crafting ingredient introduced in the April 28, 2011 Patch. It is depicted as a fossil of a fish's skeleton encased in a chunk of hardened earth. By earning the "Moustache Scientist" achievement in SpaceChem, one can unlock this element to craft the Fishcake.
As a crafting ingredient
|| Moustache Scientist|
Beat the assignment "Moustachium 604".
The second bonus Australium level beaten in SpaceChem grants the 'Fish' along with one Moustachium Bar.
- The description of the item is a reference to a chapter in the SpaceChem backstory, in which a researcher Angela tells the narrator that Fishcakes are, "packed with protein".
April 28, 2011 Patch
- The 'Fish' was added to the game.