Herring are ecologically important forage fish, recognizable by their dense schooling behavior and silvery appearance. These marine species are found in vast numbers across the North Atlantic and North Pacific Oceans. They play a significant role in the marine food web, transferring energy from smaller organisms to larger predators like seabirds and whales. Their diet consists almost entirely of small organisms that drift or weakly swim in the water column, a feeding strategy that sustains their immense populations.
The Core Diet of Adult Herring
The staple diet of mature herring is dominated by zooplankton, the tiny animal organisms drifting in the sea. This crustacean-heavy menu provides the energy necessary to support their large body mass and active lifestyle. The adult herring diet consists primarily of various copepod species, which are small, numerous crustaceans.
Larger zooplankton are also consumed, particularly euphausiids, commonly known as krill, a highly energetic food source. Herring are opportunistic feeders, meaning their exact prey composition changes based on local availability and the time of year. Their consumption is focused on these small, planktonic crustaceans.
Shifts in Feeding Habits Across the Life Cycle
The diet of a herring changes as it develops from a newly hatched larva into a mature adult. Larvae initially rely on a yolk sac for nutrients, which sustains them before they begin external feeding. Once the yolk is depleted, the first-feeding larvae must find suitable prey quickly.
These tiny larvae initially target very small organisms, such as copepod nauplii (the juvenile stages of copepods), single-celled protists, or microalgae. As the herring grow, their gape size and digestive system mature, allowing them to consume progressively larger prey. This size-dependent shift means juveniles transition from these microscopic items to the larger, energy-rich adult copepods and krill that characterize the adult diet.
How Herring Consume Their Prey
The primary method herring use to acquire food is known as filter feeding or ram suspension-feeding. The fish swim forward with their mouths open, continuously taking in large volumes of water that contain their microscopic prey. Specialized structures called gill rakers are responsible for straining the food from this water.
The gill rakers are long, comb-like projections located on the gill arches, and they are closely set together. As water flows over the gills for respiration, these rakers act like a fine sieve, trapping the small zooplankton. The concentrated food particles are then passed down the throat for digestion. This method is particularly effective when herring are feeding in dense schools within areas of high plankton concentration, allowing them to process vast quantities of water.