R'lyeh has been off the fish standard for ages. Since at least 1925, the grand old Bank of R'lyeh has been minting its own currency in the form of these heavy metal coins (they tried paper, but that's not so underwater-friendly).
With artwork by Heather Hudson, this coin is 1.75 inches in diameter and 3.5mm thick, an has an Antique Silver finish. The front features Great Cthulhu and the words "Iä! Iä! Cthulhu Fhtagn" and "Eldritch 2013." The back shows the island of R'lyeh and the words "Bank of R'lyeh," as well as "Ph'nglui mglw'nafh Cthulhu R'lyeh wgah'nagl fhtagn" around the edge.