Marcus Elieser Bloch (1723-1799) was a German medical doctor and naturalist. He is generally considered one of the most important ichthyologists of the 18th century.
Bloch was born in Anspach and practised as a physician in Berlin. He is best known for his encyclopedic work in ichthyology. Between 1782 and 1795 he published his Allgemeine Naturgeschichte der Fische, a 12-volume, beautifully illustrated comprehensive work on fishes. The first three volumes describe fishes in Germany and were entitled Oeconomische Naturgeschichte der Fische Deutschlands, the remaining volumes dealt with fishes from other parts of the world and were entitled Naturgeschichte der ausländischen Fische.
Bloch's collection of about 1500 specimens is today preserved at the Museum for Natural History (Naturhistorisches Museum) of the Humboldt University of Berlin.