Fish printing: Gyotaku prints are prints or rubbings made by putting pigment onto a fish and making a print directly from the fish. In ancient Japan, the purpose of these prints were to record how large a fish was caught. By Barry Singer
You dont need to be an ichthyologist but it helps to be an angler. Begin by catching a fish. You will find out that some species work better than others. generally flat fish with large scales are best. Salt water or fresh water, it doesnt matter.