What is "clupea harengus"

Herring \Her"ring\ (h[e^]r"r[i^]ng), n. [OE. hering, AS. h[ae]ring; akin to D. haring, G. h["a]ring, hering, OHG. haring, hering, and prob. to AS. here army, and so called because they commonly move in large numbers. Cf. Harry.] (Zo["o]l.) One of various species of fishes of the genus Clupea, and allied genera, esp. the common round or English herring ( Clupea harengus) of the North Atlantic. Herrings move in vast schools, coming in spring to the shores of Europe and America, where they are salted and smoked in great quantities. Herring gull (Zo["o]l.), a large gull which feeds in part upon herrings; esp., Larus argentatus in America, and Larus cachinnans in England. See Gull. Herring hog (Zo["o]l.), the common porpoise. King of the herrings. (Zo["o]l.)

1. The chim[ae]ra ( Chimaera monstrosa) which follows the schools of herring. Called also rabbit fish in the U. K. See Chim[ae]ra.

2. The opah.

Syle \Syle\, n. [See Sile a young herring.] (Zo["o]l.) A young herring ( Clupea harengus). [Also written sile.]

But our folk call them syle, and nought but syle, And when they're grown, why then we call them herring.
--J. Ingelow.