add image to my layout with size proportional to dimension of screen android

add image to my layout with size proportional to dimension of screen android

In my application i have an image that should have 25% width and height of
screen. I hope this is clear. This is what i'm already tried but doesn't
work. Thank you.
<ImageView
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:layout_weight="0.25"
android:src="@drawable/fish"
android:scaleType="fitCenter"
/>