Herring eat only plankton, which are tiny plant and animal species in the ocean. Plankton come in many varieties, ranging from tiny arrow worms to algae. In order to feed, herring swim through water with their mouths open, filtering the plankton out of the water. They generally spend most of the daytime in the deep waters, rising to the surface to feed at night when predators are less active.
Herring live in large schools, or groups, throughout the Pacific, Indian and Atlantic Oceans. There are several species of herring, but they all share similar characteristics. They have silver-colored skin, one dorsal fin and protruding lower jaws. Herring have a narrow body shape and pointed, tapered snouts with large eyes and yellowish gills. Their size varies by species. Atlantic herring can grow to about 18 inches long, while Baltic herring are typically 16 inches long. Pacific herring are the smallest at approximately 15 inches long.
Herring have many predators, including dolphins, seals, sea lions and whales. They are also preyed upon by larger fish, such as tuna and salmon. Predators often prey on herring by surrounding an entire school of the fish and causing them to swarm into a tight ball before easily picking herring out of the packed ball.