"Awesome fish!!" 5th graders exclaimed as Japanese artist Naoki lifted the rice paper revealing his Gyotaku (fish print) in the video here. They said the same thing as they lifted the regular copy paper (taken from the printer) to see their own prints. Students used black cake tempera, being sure NOT to add too much water so they would get crisp, clear prints.
My first year of teaching, MANY years ago, I did this with real fish. It worked just fine, but I do remember that 1st graders were a bit reluctant to touch the dead fish -- even with a paintbrush!! This year I splurged and ordered a set of 5 rubber fish from SAX ( here). I put each one in an aluminum tray, which worked really well to define the space and cut down on mess.
While one group printed, the rest of the class worked to create their background underwater scape. I posted several photos of sea plants on the whiteboard for reference and modeled how to press hard with the crayons. I asked that they make each plant have AT LEAST two colors in them, reminding them of previous work we have done with creating dimension by shading one side of a shape. I also asked that their plants of variety of height, color, shape, etc. and that they try to produce the feeling of movement that would be created by moving currents under the water.
When it was time for their watercolor wash, I asked students to stand and mentally plan their steps. (1. quickly brush plain water everywhere, 2. quickly drop blue liquid watercolor paint into the water, blending with the tip of the brush, and 3. adding drops of green or purple (cool colors) if they wished. I had them use cake tempera for this last step.) All painting was done standing up to help with the speed. The key here, of course, is to not overwork the paper. Even 5th graders seem to still want to keep painting over the same areas over, and over, and over.... you get the idea!!
I was motivated to try this process again after so many years by several gyotaku projects posted on other websites last year. You can see these other approaches posted here on my Pinterest Printing Board.