Herring (Clupea harengus) belongs to the order of bony fishes (Teleostei) called Physostomi, and characterised by the existence of an open communication between the air-bladder and the gut. The family Clupeidae is distinguished by the following characters: There is a single short dorsal fin near the middle of the dorsal edge of the body, also a single anal fin. The pelvic fins are abdominal in position, as in all Physostomi. Body covered with thin cycloid scales, head naked, barbels absent. Maxillary bones composed of at least three movable pieces. Branchial apertures very wide. The stomach has a posterior prolongation, which communicates with the air-bladder at its extremity; pyloric appendages numerous. Lateral line usually absent. The genus Clupea, which includes the herring, sprat, pilchard, and shad, is thus defined: Body compressed, with the scales of the ventral edge keeled, each keel projecting posteriorly into a point, so that the edge is serrated. Upper jaw not projecting beyond the lower. Cleft of the mouth of moderate width. Teeth, when present, rudimentary and deciduous. Caudal forked. C. harengus is distinguished by having an ovate patch of minute teeth on the vomer; the serrations of the ventral edge are weak; the pelvic fins arise behind the front end of the base of the dorsal. These characters distinguish the herring from the sprat. From the pilchard it is easily distinguished, as that species has much larger scales, and has radiating ridges on the operculum which are absent in the herring. The shad, of which there are two kinds, are much larger, and have opercular ridges like the pilchard. The air-bladder in the herring has an opening to the exterior behind the anus. The herring is a pelagic and gregarious fish, living on the small pelagic organisms, especially Crustacea, which swarm in the sea. The species occurs throughout the German Ocean and the North Atlantic, both on the American and European sides, and also the seas to the north of Asia. Enormous shoals of herring approach the coast every summer in order to spawn, and it is then that the great fisheries are carried on. There are in most places two spawning periods, but the number of those which spawn in winter or spring is always much smaller. The summer spawning season varies in different latitudes. On the east coast of Britain it occurs in June and July at Wick, July and August at Peterhead and Aberdeen, August and September at Yarmouth, September and October off Kent, while on the south coast of England only one spawning period has been observed, namely in January. This corresponds to the winter spawning in the north, which at the mouth of the Firth of Forth takes place in January and February.
The eggs of the herring are small and numerous, and are heavy and adhesive, so that when shed they adhere to the stones, shells, and hydroids, or other material of the sea-bottom. The spawning-ground chosen is always hard, rough, and often rocky, so that it is usually ground which trawls cannot be worked over. The same spawning-grounds are annually visited by the winter-spawning herring. Two such grounds are accurately known—one to the west of the isle of May at the mouth of the Firth of Forth, and one off Ballantrae on the west coast of Scotland, in Ayrshire. None of the summer spawning-beds have been actually discovered, though it is certain that there are acres of them along the east coast of Britain. It is probable that herring remain in Loch Fyne all the year round, and young and half-grown herring are often found in estuaries at various times of the year, ascending as far as the tides extend.
The artificial fertilisation of the herring's ova and their hatching in aquaria are easily effected, and have been carried out several times by various experimenters. But the artificial propagation has never been carried out on a large scale for the sake of artificially maintaining or increasing the supply of herrings, because it has never yet been proved that the supply has anywhere continuously diminished in consequence of the enormous captures which are annually made. The abundance of the fish at a particular place varies capriciously from year to year, and at different periods of time. On the coast of Bohuslän, in the south of Sweden, multitudes of herring have appeared within the last few years after they had deserted that coast for about seventy years.
Herring-eggs were first hatched under observation by Prof. Allman, in Scotland, in 1862; the eggs in this case were dredged from the bottom off the isle of May. In 1874-78 the eggs were both fertilised and hatched artificially by the German Fishery Commission at Kiel. The development has been described by Kupffer, in 1878, in the annual report of the Kiel Commission. Artificial hatching has also been carried out by the United States Fish Commission. The eggs, when pressed from the fish, are received on glass plates, to which they adhere, and are then developed in a current of pure sea-water. The larva, when hatched, is very slender and elongated: it is perfectly transparent, and at once commences to lead a pelagic existence in the surface waters of the sea. Herring-spawn at the bottom of the sea is largely devoured by flat-fish and haddocks, which are extremely fond of it.
Meyer, of the Kiel Commission, noted the growth of the herring in captivity: when first hatched it is th to of an inch long; one month after hatching it is ds of an inch; at two months it is inch; at three months about 2 inches. Then it grows at the rate of about half an inch per month, so that at six months it is about inches, and at one year inches. Thus the herring is mature at two years old, but not full-sized. The so-called 'maties,' which are mature fish, and shed spawn and milt, are probably the two-year-old fish spawning for the first time, while the full-grown herring are three or four years old.
For detailed information on the natural history of the herring, see Nature (vol. xxvi. p. 607, and vol. xxix. p. 539) and the 'Jahresberichte' of the Commission zur Untersuchung der Deutschen Meere, which contain numerous elaborate memoirs on the subject. See FISHERIES.