A manuscript catalogue of the fishes of the Baltic Sea, and of the rivers and lakes of Sweden, the only known original work of the Swedish ichthyologist Peter Artedi (170535) by his own hand, is translated into English for the first time, and its contents assessed in light of Artedi's contribution to the development and philosophy of Linnaean systematics. Appended accounts of Swedish cetaceans and terrestrial mammals are also discussed, as well as Artedi's 'principles of ichthyology', the methodology later employed in his magnum opus, the Ichthyologia of 1738. Evidence that Artedi presented the manuscript to Sir Hans Sloane as a way to introduce himself during his visit to London in 1734 is also provided.