An anonymous critique of Peter Artedi’s (1705‒1735) Ichthyologia sive opera omnia de piscibus, the latter edited and published posthumously by Carolus Linnaeus (1707‒ 1778) in 1738, is shown to have been written by the Prussian jurist and naturalist Jacob Theodor Klein (1685‒1759), and sent to Hans Sloane (1660−1753) in London for his approval. The critique is transcribed and translated, and its contents assessed in light of Artedi’s contribution to Linnaean systematics. While in some ways highly critical of Artedi, Klein must have been well aware that by criticizing Artedi he was, by association, criticizing Linnaeus as well. Linnaeus’s editorial contributions to the Ichthyologia as well as his on-going antagonistic relationship with Klein are also discussed.