This process began with some paper sketches of elements within the game - thinking about the relative size of the fish, obstacles etc. and how they appear on the screen.
Next, some pen and ink sketches were used to have more clear designs to work from when producing the digital version. This ensures the vector images aren't too stiff and geometric: if working directly to vector, it can be tempting to use more generic, oversimplified shapes and the designs become unimaginative.
Finally, the designs are drawn digitally in a vector format. This allows easier resizing of the sprites to suit different screen sizes.