Ernst Johannes Schmidt (2 January 1877 – 21 February 1933) was a Danish biologist credited with discovering in 1920 that European eels migrate to the Sargasso Sea to spawn.

[2] Schmidt began his studies of natural history at the University of Copenhagen under professor of botany Eugen Warming (1841–1924), and obtained an MS degree in biology in 1898.

He obtained a grant from the Carlsberg Foundation to study the flora of the coastal areas of Ko Chang in then Siam, including both mangrove trees and microalgae.

He made his doctoral thesis in biology and botany, on shoot architecture of mangrove trees and Eugen Warming served as faculty opponent in October 1903.

Schmidt worked in parallel on phycology, where he described the genus Richelia (filamentous heterocyst-forming Cyanobacteria dwelling inside diatoms), on plant physiology and genetics, especially of hops, and on large-scale oceanography and ichthyology.