Small, primitive, bony fish related to the sardine and the anchovy. Herrings are relatively small but very abundant; they swim in huge schools, feeding on plankton and small animals and plants. Most herring family species are ocean-dwelling, living in salt water as adults, but returning to freshwater to spawn, and spending the early part of their lives in freshwater. Other herring family members are strictly freshwater fish. The adult common herring, found in temperate and cold waters of the North Atlantic, is about 30 cm long with silvery sides and blue back.