The flying fish is found in some medieval encyclopedias. It is a fish that must sleep to live, and goes out of the ocean onto dry land to do so.

Thomas of Cantimpré has an account of another fish called ezochius maris, but the description is entirely different.

In modern taxonomy, flying fish are in the family Exocoetidae and some are in the genus Exocoetus. They do not fly like birds, but leap out of the water and glide long distances with their wing-like fins. They do not sleep on land. The Latin name exocoetus is from a ancient Greek word that means literally "sleeping outside".