Anchovies are small, schooling fish common in marine waters worldwide, with over 140 species identified. These slender fish are frequently classified as forage fish, meaning they are a primary food source for many larger predators in the ocean. Anchovies are considered omnivores because their diet consists of both plant-like and animal-like matter, fitting the definition of an organism that feeds on both plant and animal substances.
Defining the Anchovy Diet
The omnivorous classification of the anchovy is based on its consumption of plankton, which includes both plant and animal components. The plant-like portion of their diet is phytoplankton, which are microscopic, photosynthetic organisms. Since phytoplankton are primary producers, they satisfy the herbivorous requirement of the anchovy’s diet.
The animal portion of their diet, fulfilling the carnivorous requirement, is zooplankton. Zooplankton are tiny animal organisms, such as copepods and the larvae of various crustaceans and fish. The specific composition of the anchovy’s diet can vary significantly depending on the local environment and the season. For instance, some adult anchovies may be strictly zooplanktivorous during their main spawning season.
Anchovies also consume small fish and fish larvae, particularly when they are larger or when plankton is less abundant. This flexibility demonstrates a high degree of dietary plasticity, allowing them to adapt to different nutrient availability across the marine ecosystem. An adult anchovy can consume approximately 5% of its own body weight in plankton each day.
The Filter Feeding Mechanism
The ability of anchovies to consume microscopic food is due to a specialized behavior called filter feeding. As the anchovy swims with its mouth wide open, water flows through the mouth and out through the gills. This process is known as ram filter feeding, where the fish relies on its forward motion to push water over the feeding apparatus.
Food particles are captured and strained from the water by bony or cartilaginous projections called gill rakers. These rakers are positioned on the gill arches and function like a sieve, preventing small food items from exiting the body. The collected food is then transferred into the esophagus for digestion.
Anchovies can switch between this passive, bulk filter-feeding mode and a more active, selective particulate feeding mode. Selective feeding allows them to target and capture larger, individual prey items like bigger zooplankton or small fish larvae. This dual feeding strategy maximizes their energy intake by efficiently processing various food particles available in the water column.
Anchovies’ Place in the Marine Food Web
The anchovy’s role as an omnivore and filter feeder positions it as a crucial link within the marine food web. They are classified as forage fish, acting as a bridge that transfers energy from microscopic plankton to a host of larger predators. By consuming both phytoplankton and zooplankton, anchovies convert energy from lower trophic levels into a form accessible to higher-level consumers.
The abundance of anchovies directly affects the breeding success and population health of many marine animals, including a variety of large fish, marine mammals, and seabirds. Commercially important species such as tuna, salmon, and swordfish rely on anchovies as a significant part of their diet. When anchovy populations decline, there can be cascading impacts throughout the ecosystem, affecting the populations of their many predators.
Anchovies also hold a significant place in commercial fisheries as a high-volume catch. They are harvested for human consumption, but a large portion is processed into fish meal and fish oil, which are used in aquaculture and livestock feeds. The management of these fisheries is directly related to the anchovy’s ecological role, aiming to sustain both the natural ecosystem and human industry.