You will need triangles in two sizes in a selection of colors. You will also need small circles precut or use hole puncher. Each child selects a large and small triangle. He puts glue under the right angle point of the small triangle and glues it to the center of the long side of the large triangle. He then selects or cuts circles and glues them to the fish for its markings. Then he glues his fish to a background paper. This could be a blue or green fingerpainting or just green or blue construction paper. Sand could be added to the fingerpaint to add texture to the painting.
A large mural sized paper could be painted and everyone add their fish in the ocean.