The Atlantic herring is a kind of herring, a fish. It can be found on both sides of the Atlantic. It can grow up to 45cm in length, weighing more than half a kilogram. It is a swarm fish, meaning many fish come together and form a "school" (or swarm) of fish. Swarms of up to 4 cubic kilometers in size have been measured of "atlantic herring", with an eastimated 4 billion individual fish. Like with so many other fishes though, commercial overfishing is posing a problem. Stocks of herring have been collapsing. 