A coffee filter
One wiggly eye
Start by coloring patches of color all over your coffee filter. Use bright colors for best results (yellow doesn't show up well on the brown coffee filter). Once your coloring is complete use a spray bottle to wet your filter. I let Munchkin shake An old sippy cup full of water on the filter (this worked fine).
Once your filter is saturated the colors will begin to run together (I had to help it a bit with my finger). Let it dry completely. The colors will be much lighter. Cut it into the shape of a fish.