flockingdemo.kv

<Fish@Image>:
    source: "images/fish.zip"
    size_hint: None, None
    size: 35, 35
    pos: self.pos
    #anim_delay: 0.25
    canvas.before:
        PushMatrix
        Rotate:
            axis: 0,0,1
            angle: root.angle - 180
            origin: self.center
    canvas.after:
        PopMatrix


<FlockingDemo>:
    canvas:
        Rectangle:
            source: "images/background.png"
            size: self.size