Anchovies are small, silver-colored schooling fish found in marine and brackish waters worldwide. They have high commercial importance due to their vast abundance and occupy a low trophic level, making them a fundamental part of the ocean food web. Anchovies are primarily planktivores, consuming large quantities of both zooplankton and phytoplankton. Efficient feeding on these microscopic organisms fuels much of the marine ecosystem.
The Anchovy Diet
The diet of anchovies is overwhelmingly comprised of plankton, organisms suspended in the water column. Zooplankton, or animal plankton, form a major energy source and include small crustaceans like copepods, euphausiids, and larval stages of larger marine organisms. Copepods are frequently the main caloric component in the diet of many anchovy species.
Anchovies also consume phytoplankton, which are microscopic, single-celled plants such as diatoms and dinoflagellates. The proportion of zooplankton versus phytoplankton consumed varies significantly based on the anchovy species, life stage, and local availability. Some adult populations may focus almost entirely on zooplankton, while others maintain a mixed diet, shifting preference based on which plankton type is most densely aggregated.
Dietary shifts can occur daily, as some anchovy species forage in the water column during the day in summer or mainly at night in winter, following the vertical migration of their prey. Juvenile anchovies often begin their lives consuming smaller plankton. The total amount of food an anchovy consumes daily can be about five percent of its own body weight.
Mechanism of Filter Feeding
Anchovies capture microscopic food through filter feeding, a specialized and highly effective process. This mechanism involves drawing water into the mouth and processing it through the gill arch system to strain out suspended particles. The key anatomical structures are the gill arches, which bear fine, comb-like projections called gill rakers. These rakers form a mesh that retains the plankton while allowing the water to pass over the gills and exit the body.
The process often relies on a technique called “ram filter feeding,” where the anchovy swims forward with its mouth held wide open. By maintaining a wide gape, the fish drives water directly through the filtering apparatus, capturing a high volume of prey efficiently. This method is energetically intensive because the open mouth increases drag, forcing the fish to switch between streamlined swimming and the slower, high-drag feeding mode.
Anchovies utilize a combination of filtration principles, including cross-flow and dead-end filtration, to separate the particles. In cross-flow filtration, the water flows parallel to the gill rakers, transporting the captured particles along the surface toward the esophagus where they accumulate. They also have the ability to switch feeding strategies to selectively pick off larger, individual prey items when the plankton patch is less dense.
Ecological Significance of Anchovy Feeding
Anchovies are categorized as “forage fish,” meaning they are small, schooling prey species that link the lower and higher levels of the food web. By feeding on plankton, anchovies transfer the energy from these primary producers and consumers upward to larger predators. This makes them a crucial intermediary species in the marine environment.
A wide range of animals, including commercially valuable fish like tuna and salmon, marine mammals, and many species of seabirds, depend on anchovies as a major food source. The abundance of anchovies is directly connected to the reproductive success and population health of these higher-trophic-level predators. For instance, the nesting success of seabirds like brown pelicans and elegant terns is strongly linked to anchovy availability.
Their high abundance and schooling behavior make them commercially important to humans. They are harvested for direct consumption, used as bait, and processed into fishmeal and fish oil. The health of anchovy populations is a major factor in the stability of both ocean ecosystems and the fishing industry.