Herring is a greasy fish of the genus Clupea which is found in the shallow and warm waters of the North Pacific and North Atlantic Ocean and the Baltic Sea. Two species of Clupea are recognized, the Atlantic herring (Clupea harengus) and the Pacific herring (Clupea pallasii) and each is divided into subspecies. Herring is a hunter, moving in large herds, and approaching the spring on the shores of Europe and America, where they are usually caught and preserved or smoked. It reaches the age of 20 to 25 years. Herring is rich in ω-3 fatty acids and vitamin A, and is one of the best sources of calcium and vitamin D.

The two Clupea species belong to the largest family Clupeidae (herrings, shads, sardines, menhadens), which includes about 200 species with common features. It is silver with a dorsal fin, which is soft, without supporting tissue. They have no lateral line and their lower jaws protrude. Their size varies according to the subspecies: Baltic herring (Clupea harengus membras) is small, from 14 to 18 cm, common herring (C. harengus) can reach 46 cm (18 inches) and the 700 grams of weight, and the Pacific herring reaches about 38 centimeters. It has greenish scales, a blue back and a silver-colored belly.