Vertebrate Zoology: Study Guide - T. A. Dauda 2014

Metazoa
Fishes
Class Osteichthyes - Subclass Actinopterygii - Order Clupeiformes

The order Clupeiformes unites the most primitive of modern bony Fishes. Their Skull undergoes relatively weak ossification. The swim bladder retains its connection to the Esophagus throughout life. The order comprises several families, the principal ones being Clupeidae (herrings) and Salmonidae (salmons).

Herrings are extremely numerous. They possess an elongated body, compressed laterally. The pelvic fins are located in the middle of the ventral side of the body, with the dorsal fin positioned above them. The lateral line organ is absent. Scales on the belly form a keel. Herrings inhabit primarily marine environments. Certain species enter rivers to reproduce. Oceanic herring is found in the White and Barents Seas, as well as in the seas of the Far East. It undertakes extensive Migrations in search of environmental conditions suitable for different life stages. For spawning, herrings approach the shores in massive schools. Spawning occurs in relatively shallow areas. The eggs are heavy, sinking to the bottom and adhering to underwater objects, most frequently Algae. This herring exhibits high fecundity: 40–280 thousand eggs.

The Caspian and Black Seas are rich in herrings. Some of their inhabitants, such as the Volga herring and the Caspian shad (chernospinka), spend their maturation and feeding period in the sea, but ascend rivers to reproduce. The Caspian shad largely dies off after spawning. Mortality among the Volga herring is not as significant. The Caspian kilka typically spends its entire life at sea, yet, much like the oceanic herring, migrates extensively in search of suitable habitats.

In the Far East, the Pacific sardine (iwashi), a fish closely related to herrings, is also widespread. It is a typically marine, highly migratory fish. It appears off the coast of Primorye in spring during its feeding migration.

The Baltic Sea is inhabited by the sprat, while the Caspian Sea is home to the closely related kilka (Black Sea sprat). Both of these species are found in the Black Sea. They are closely related to true herrings. In the Russian fisheries industry, Clupeidae occupy the leading position.