With the success of its first booklet pane showing colorful, commemorative stamps, the U.S. Postal Service quickly came back with this set of five stamps, printed in booklet form, featuring fish common to U.S. waters. Most of the fish of the world are continental, living as part of the fresh -water system on land or in the sea staying near and influenced by coastal waters which are very rich in nutrients. Only about 3.5 percent of the Earth's land surface (which is 30 percent of the total surface) is covered by fresh water. More than 20,000 fish species inhabit these waters, a number equal to or exceeding the number of all other vertebrate species combined.