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Atlantic herring Clupea harengus is the most abundant fish species of the world, living in large schools (swarm). Growing up to 45 centimeters in length and more than half a kilogram in weight, they feed on copepods, krill and small fish and are food for seals, whales, cod and other larger fish.
Adult Atlantic herring, Photo by Uwe Kils The Atlantic herring fishery has long been an important part of the economy of New England and the Canadian Maritime provinces, because the fish congregates relatively near the coast in massive schools, notably in the cold waters of the semi-enclosed Gulf of Maine and Gulf of St. Lawrence. North Atlantic herring schools have been measured up to 4 cubic kilometers in size, containing an estimated 4 billion fish.
A typical school of herring heads to shore during mating season, usually during the fall. Each female lays from 50,000 to 90,000 eggs, which sink to the ground and stick to it via an adhesive covering.
 Slow motion macrophotography video (50%, looping, each image shifted to compensate the rolling microturbulences from the waves) of feeding juvenile herring (38 mm) on copepods - the fish approach from below and catch each copepod individually. In the middle of the image a copepod escapes successfully to the left  In this sequence a herring attacks four times in a row. In the third attack the copepod is visible between the wide opened sides of the mouth. The opercula are spread wide open to compensate the pressure wave which would alert the copepod to trigger a jump. External links
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