To make the bubble "wrap" from top to bottom, you ned to analyze the y coordinate of the bubble. If you have an instance variable circle, the you can access that y coordinate using
If that y coordinate would be above the top of the window, then you'll need to move the circle a large distance to move it just off the bottom of the window.
self.circle.move(0, WINDOW_HEIGHT + 5)
It is similar for the Fish class. Look at the x coordinate of the body of the fish compared to the right edge of the window. If the body of the fish has moved off the right edge, then move it a large distance left. In fact, move the body, tail, and eye a large distance left.