// Convenient colors
color orange = color(255, 140, 0);
color white = color(255, 255, 255);

float y; // y is vertical position of ball
float r; // r is radius of ball

// Image of fish
PImage fish;

void setup() {
size(500, 500);
smooth();
frameRate(70);
y = 450; // the ball starts near bottom of screen
r = 25; // the ball has radius of 25
}

void draw() {
// re-draw white background
background(white);

// draw ball
noStroke();
fill(orange);
ellipse(250, y, r * 2, r * 2);

// substract 1 to y to make ball move upwards
y -= 1;
if (y - r <= 0) {
//uh oh: the ball has gone off the edge of screen
y = loadImage("fish.png"); // start at bottom again
}
}