The Windows 7 Beta 1 (download link) features a Siamese fighting fish in the middle of the default desktop, which over rides the default PDC 2008 wallpaper. Now what is a fighting fish doing on the default screen?
The Siamese fighting fish (Betta splendens), also known as the "betta fish" or just "betta", is one of the most popular species of freshwater aquarium fish. It is native to the rice paddies of Thailand and called pla-kad or pla-kat ("Biting Fish") in its native Thailand, Wikipedia. That’s right! the Siamese fighting fish is pronounced as the Beta fish.
No more appropriate creature could’ve been placed on the desktop of build 7000 of Windows 7, it is the Beta build!
Source:→ MSDN Blog