Because of the pretty of the image self, I believe it will be still included in the final release.

The blue betta splendens fish is still included in later Windows 7 version, but not as default as in Beta version. … Nevertheless, the process of selective breeding has produced Betta splendens fish with a wide range of colors, including the blue and red, as the specimen on the Windows 7 background. However, Microsoft has chosen a specific variety of betta. The betta fish featured in Windows 7 Beta on the default background is native of Thailand. It was included starting in Beta version, simply because this very popular freshwater fish is pronounced as beta.

The little fish with red fin in the wallpaper is called Siamese fighting fish, also known as the Betta. But do you know the story behind it why it’s been chosen? Yes, Microsoft didn’t pick it up for no reason.

If you have used Windows 7 beta version, you might still remember this little fish that came up as the default wallpaper in beta version.

Windows 7 beta wallpaper