Fish Tycoon for Windows Mobile devices was developed for displays that have a resolution of 240 x 320 pixels, which was the standard 5 years ago when the game was released. 480 x 640 devices typically offered a mode (pixel doubling) that allowed full-screen display of 240 x 320 applications. Since your HTC Touch Pro 2 has a screen size of 480 x 800, the game will not fill the entire screen unless there is a display mode setting in your device to 'stretch' the game to fit your screen.
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Barbara
Unicorn
Last Day of Work