What Do Anchovies Eat? Their Diet and Feeding Habits

Anchovies eat plankton, with tiny crustaceans called copepods making up the bulk of their diet across virtually every species and ocean basin studied. But the full picture is more varied than “small fish eats small things.” Anchovies can switch between two entirely different feeding strategies depending on what is available, their diet shifts dramatically from larval stage to adulthood, and they occasionally eat their own eggs. How they find and capture food also involves one of the most unusual visual systems in the animal kingdom.

The Core Diet

If you opened the stomach of a typical adult anchovy, you would mostly find copepods, the rice-grain-sized crustaceans that dominate the world’s zooplankton. Calanoid copepods are especially prominent. Beyond copepods, anchovies consume a rotating cast of other zooplankton: small shrimp-like organisms called euphausiids, fish eggs and larvae, crab larvae, and various other drifting invertebrates. Some species also take in phytoplankton, particularly diatoms, though plant matter generally contributes far less to their energy intake than animal prey.

The European anchovy in the Mediterranean, for instance, feeds on a wide range of planktonic prey throughout its life, from tiny nauplii as a juvenile to larger copepods and euphausiids as an adult.¹ Off Peru, the anchoveta takes in diatoms alongside its zooplankton diet, a combination that reflects the extraordinary productivity of the Humboldt Current upwelling system.² In the North and Baltic Seas, European anchovies eat similar zooplankton but also consume larval fish, making them both competitors and predators of other commercially important species like herring.³

Two Ways of Eating

Anchovies do not feed in just one way. They switch between two distinct strategies depending on the size and concentration of their prey. When food particles are large enough to see individually, an anchovy bites at them one at a time, the way most fish eat. But when the water is full of very small organisms, the fish opens its mouth wide, extends its gill covers, and swims forward, straining food out of the water like a living sieve. This filter-feeding mode is closer to what baleen whales do than what most people picture when they think of a fish eating.

Laboratory work on the northern anchovy showed this switching behavior clearly. When researchers offered adult brine shrimp at high concentrations, the anchovies picked them off individually with biting attacks. But when they offered brine shrimp nauplii, which are far smaller, the same fish shifted to filtering.⁴ The trigger seems to be a combination of prey size and density: small, abundant food makes filtering more energy-efficient, while sparse or large prey favors targeted strikes.

The balance between these two modes varies across species. Japanese anchovy, studied off the coast of Kyushu, leans heavily toward filter feeding compared to other planktivorous pelagic fish in the same waters. Researchers found that the Japanese anchovy’s stomach contents were explained more by its preference for filtering than by any physical difference in its gill apparatus.⁵ In other words, it is not just that anchovies have the equipment to filter; some species behaviorally choose filtering even when they could bite.

The Gill Raker System

Filter feeding requires specialized anatomy, and anchovies have it in their gill rakers. These are comb-like structures lining the inside of the gill arches, and in filter-feeding anchovy species, they are fine enough to trap organisms as small as a few hundred micrometers across. The rakers work like a mesh screen: water passes through while plankton gets caught, then swept toward the esophagus.

What is interesting from an evolutionary perspective is that the gill raker design used by filter-feeding anchovies was not originally built for that purpose. A phylogenetic study of gill raker development across the anchovy family found that the characteristic pattern of tiny tooth-like projections on the rakers evolved before filter feeding itself appeared in the genus Engraulis. Related anchovy species that share the same basic raker structure do not filter feed at all.⁶ So the anatomy came first, and filter feeding was a behavioral innovation that co-opted an already-existing structure. This is a common pattern in evolution, but it is a good reminder that anchovies did not “grow” their gill rakers in order to filter feed; they had them and found a new use.

What Larvae Eat and Why It Matters

Anchovy larvae are not miniature versions of the adults. A newly hatched anchovy is a few millimeters long, transparent, and feeds on the tiniest available plankton: single-celled organisms, the smallest copepod larvae, and other microzooplankton. As the fish grows, it gradually shifts to larger prey. This transition is a critical bottleneck. If the right food is not available at the right time, entire year-classes of anchovies can fail to recruit into the adult population.

A study using nitrogen isotope records preserved in anchovy scales showed that larval diet quality was closely linked to the boom-and-bust cycles of anchovy populations off the California coast. During the population boom from roughly 1962 to 1986, larvae were feeding at a lower position in the food web, meaning they were getting their energy more directly from primary production. During the subsequent bust, the food chain lengthened, and energy transfer to larvae dropped by about a third. In practical terms, the larvae were eating prey that had themselves eaten more intermediaries, so less total energy made it up to the larval anchovy.⁷ The finding suggests that what anchovy larvae eat, and how efficiently they get energy from the base of the food web, can drive population-level consequences that last decades.

Egg Cannibalism

Anchovies are not strictly herbivore-adjacent plankton grazers. They will eat their own species’ eggs, and this cannibalism can be a significant source of both calories and egg mortality. Research on the Argentine anchovy tracked egg cannibalism over multiple spawning seasons in the 1990s. In most years studied, anchovy consumption of their own eggs accounted for roughly 15 to 33 percent of total egg mortality within the study area. One individual fish was found with 433 eggs in its stomach.⁸

The cannibalism was not random. It tracked food availability in a predictable way. In 1999, when copepod densities in the water column were high (around 69,000 per square meter, compared to 6,000 to 53,000 in previous years), egg cannibalism dropped to about 2 percent of egg mortality, and the fish ate three times as many copepods as in earlier years. When their preferred food was abundant, the anchovies largely left the eggs alone. When copepods were scarce, egg cannibalism ramped up and could supply over 90 percent of the daily energy a female needed for reproduction.⁸ This makes cannibalism look less like aberrant behavior and more like a flexible energy strategy, something the fish fall back on when conditions are poor.

How Anchovies and Sardines Divide the Menu

Anchovies and sardines live in the same waters across much of the world, and both are planktivores. This raises an obvious question: why don’t they just eat each other out of house and home? The answer is that they partition the food supply, primarily by prey size.

Off Peru, sardines eat smaller copepods and fewer euphausiids than anchoveta do, and the phytoplankton fraction of their respective diets comes from different groups: sardines eat more dinoflagellates while anchoveta eat more diatoms.² In the Mediterranean, a detailed comparison of juvenile European anchovy and sardine in the Gulf of Lions found significant dietary differences tied to differences in their mouth and gill anatomy, and concluded that the two species do not compete for food even when living side by side.¹

This size partitioning has been observed in other upwelling systems too, suggesting it is a general rule rather than a quirk of one region. Anchovy species tend to target somewhat larger zooplankton, and sardine species tend to go finer. Their gill raker spacing differs accordingly, with sardines generally having finer-meshed rakers that can trap smaller particles. The result is two fish that look superficially similar but are tapping into different slices of the plankton community.

When and How Much They Eat

Anchovies are primarily daytime feeders. Stomach fullness studies of the European anchovy during its spawning season in the northwest Mediterranean found that stomachs were emptiest in the hours before dawn and fullest in the late afternoon, between roughly 5 and 6 p.m.⁹ This makes sense given that filter feeding and visual particulate feeding both benefit from daylight. An anchovy swimming through a dense plankton patch at night would miss much of what is there.

The daily ration, meaning how much food an anchovy eats per day relative to its body weight, was estimated at about 4 percent of body weight in that same Mediterranean population during spawning season.⁹ That is a modest amount compared to some other fish, and it was lower than estimates for the same species in the Black Sea. For a fish that typically weighs 10 to 30 grams, 4 percent translates to less than a gram of food per day. Given that plankton are mostly water, the actual dry mass consumed is a tiny fraction of that, which underscores how energy-dense copepods and other zooplankton are relative to their size.

Trophic Position Varies by Habitat

Not all anchovies sit at the same level in the food web. The bay anchovy, a small species common along the U.S. Atlantic coast, occupies a higher trophic position than you might expect from a planktivore. Isotope studies estimated its trophic level at roughly 3.5 to 3.8 on the continental shelf, placing it as a secondary to tertiary consumer rather than a simple herbivore-adjacent grazer.¹⁰ That means bay anchovies are eating things that have themselves already eaten other animals.

Habitat matters too. Bay anchovy cohorts that grew up on the continental shelf drew nutrition roughly equally from pelagic (open-water) and benthic (bottom-associated) food webs, while cohorts from estuaries got more than 80 percent of their biomass from pelagic sources alone.¹⁰ Shelf-dwelling bay anchovies also appeared to be in better body condition, hinting that access to a more diverse food web paid off in terms of growth and energy reserves. The broader point is that “anchovy diet” is not a single fixed thing. It shifts depending on species, geography, season, and habitat type.

How Anchovies See Their Food

Anchovies have an unusual trick up their sleeve when it comes to finding food: they can detect polarized light. Most vertebrates cannot do this. Anchovy retinas contain triple cones, an arrangement of photoreceptor cells where the internal membrane layers are oriented in perpendicular planes, providing a physical basis for sensing the polarization angle of incoming light. At the same time, the different components of these triple cones absorb light at different peak wavelengths, around 475 and 502 nanometers, giving the fish a form of color vision as well.¹¹

Anchovies are unique among vertebrates in combining both color and polarization vision within the same retina. Polarization sensitivity could help them spot transparent zooplankton that would otherwise be nearly invisible against the open water. Many planktonic organisms have body structures that alter the polarization of light passing through them, so an anchovy with polarization vision would perceive contrast where a human eye would see nothing but water. This makes the anchovy’s visual system one of the most specialized among small pelagic fish and helps explain how a filter feeder can also function as a selective particulate feeder when conditions call for it.

Microplastics in the Anchovy Diet

Because anchovies filter large volumes of seawater through their gills, they inevitably ingest whatever is suspended in that water, including microplastics. Studies from both the Pacific and Mediterranean have documented this. In Monterey Bay, California, about 58 percent of northern anchovies sampled contained suspected anthropogenic microparticles, predominantly fibers.¹² In the northwest Mediterranean, 30 to 40 percent of European anchovies had ingested anthropogenic microparticles, averaging about one fiber and a fraction of a fragment per fish.¹³

The Mediterranean study found that fiber ingestion correlated with how full the gut was, suggesting that fibers enter through the same filtering mechanism that captures plankton. Plastic fragments, on the other hand, were mostly transparent, raising the possibility that the fish actively mistook them for zooplankton and bit at them. Most affected fish had only a single particle in their stomach, and the researchers estimated that particles passed through within about a day.¹³ This short gut-transit time limits individual exposure, but because anchovies feed daily and sit near the base of marine food webs, even modest per-fish contamination can magnify through the food chain as seabirds, larger fish, and marine mammals consume anchovies in bulk. In the Monterey Bay study, 100 percent of common murres, a seabird that eats anchovies heavily, contained microparticles.¹²

Anchovies as Prey

Understanding what anchovies eat is only half the ecological story. Anchovies themselves are among the most important prey species in ocean ecosystems worldwide. They occupy a critical middle position in the food web: they convert the enormous biomass of plankton into fish flesh that is large enough for bigger predators to eat efficiently. Seabirds, marine mammals, tuna, swordfish, squid, and many other predatory fish all depend heavily on anchovy populations. When anchovy numbers crash, the effects ripple outward. Seabird breeding failures, for instance, have been linked to poor anchovy availability in both the California Current and the Benguela Current off southern Africa.

This position as a “waist” species in the food web means that anything affecting the anchovy’s own food supply has outsized consequences for the broader ecosystem. A shift in plankton composition that reduces the quality of larval anchovy food, as documented in the California Current isotope study, does not just affect anchovies. It propagates upward through every species that depends on anchovies for calories. For fisheries managers, this means monitoring plankton communities is not just an academic exercise but a practical early warning system for the health of anchovy-dependent fisheries and the ecosystems around them.