HERRING, a fish belonging to the genus Clupea, which is the most widely distributed of all fish genera. The commonest members of the genus are, besides the herring (C. harengus), the sprat (C. sprattus), the pilchard (C. pilchardus), the Allis shad (C. alosa) and the Thwaite shad (C. finta). Herrings are caught in great numbers in the North sea, off the west coast of Norway, in all the waters off the British Isles and in the Baltic sea. In the Atlantic ocean they are found from north of Cape Cod to Green land, around Iceland, the Faeroes, and also in the White sea, and varieties of the species occur in the Caspian sea and the Black sea. The herring of the North Pacific ocean is C. pallasi, but is hardly distinguishable from C. harengus.
To countries bordering the North sea, the herring fishery is of paramount importance, as is shown in the following table of land ings for 1925:— "Whitebait herring"-8-12cms. the end of their first year. The second year is spent in the open sea, feeding main ly on copepods, and during this time they grow rapidly to 16-19 cms. It is not until they are becoming adult that they appear in shoals off the coast. The onset of maturity, accompanied by a decrease in growth-rate, takes place at different times in the vari ous seas where herrings are caught.
In the North sea they mature mainly in the third or fourth year, while in Norway they do so at from five to eight years of age. Size also varies in different localities, fish of oceanic waters having a larger yearly growth than those of more enclosed areas. A herring of 28cms. (II") would be large for the southern North sea, while fish of 34cms. (13-") or more are common in Nor wegian shoals.
In the Baltic sea, with its low salinity, mature herrings of iocms. are found.
The old conception of herring migrations was that all the fish of the North Atlantic and neighbouring waters wintered within the Arctic Circle, and in spring came south in large columns to spawn. It is now known that the movements are more limited, and that Norwegian herrings and those from the North sea, the Baltic, and the western English channel all differ structurally, the differences of these "races" being shown by the numerical varia tions of such characters as vertebrae, fin rays, and the scales along the "keel" of the fish. The cycle of migration is in three main parts—the feeding movement, when the genital organs are devel oped; the movement to the spawning grounds, and the dispersal after spawning.
On the scales of the herring there are concentric annual rings (like those in trees) from which age can be determined, and in vestigation has shown that mature herrings visit the same grounds each year until each year-class in turn becomes extinct. Commer cially, herrings are salted or pickled for export. Herrings are also cured as kippers, bloaters, or "red-herring," and the iridescent substance, guanin, from their scales, is used in the manufacture of artificial pearls. (W. C. H.)