The American eel, Anguilla rostrata, is a migratory fish inhabiting a wide array of aquatic environments from freshwater rivers to coastal marine areas. This species exhibits a highly diverse and adaptable diet, which is influenced by its life stage and the specific habitats it occupies throughout its range. Their feeding habits are largely opportunistic, allowing them to thrive in varied conditions.
General Diet of American Eels
American eels are carnivorous and opportunistic feeders, with their diet primarily consisting of aquatic organisms. During their longest feeding phase, known as the yellow eel stage, they consume a broad spectrum of prey. Smaller yellow eels typically feed on benthic invertebrates, with insects being a significant component of their diet.
As yellow eels grow larger, their diet shifts to include bigger prey items. Eels over 35 cm in length frequently consume fish and crayfish. Other common food sources for yellow eels include various crustaceans, such as shrimp and crabs, clams, worms, and even frogs. They are primarily nocturnal feeders.
Dietary Changes Through Life Stages
The diet of the American eel undergoes significant transformations as it progresses through its distinct life stages. The initial larval stage, known as leptocephali, are believed to be non-feeding. These larvae drift with ocean currents for up to a year before reaching coastal waters.
Upon reaching coastal areas, leptocephali metamorphose into glass eels, which then become elvers. While glass eels are initially thought to be non-feeding, later-stage elvers begin to feed on small aquatic insects, small crustaceans, and dead fish. They exhibit non-selective feeding behavior, consuming the most abundant benthic insects in their shallow tidal habitats. As they mature into yellow eels, their diet diversifies extensively. The final life stage, the silver eel, ceases feeding entirely as it prepares for its long oceanic migration back to the Sargasso Sea for spawning. During this phase, their digestive tract degenerates, relying on stored fat reserves for energy.
Foraging Behavior and Habitat Influence
American eels acquire food through specific foraging behaviors, which are significantly influenced by their surrounding habitat. They are predominantly nocturnal, seeking shelter during daylight hours. Their ability to move across varied terrains, including over land, allows them to access different foraging grounds.
Eels possess an acute sense of smell, which assists them in locating prey in low-light conditions. When capturing larger prey, they employ a rotational feeding technique, twisting their bodies to tear off pieces of food. The specific environment an eel inhabits directly impacts the availability and type of prey. For instance, eels in freshwater rivers primarily consume aquatic insects, while those in brackish water environments, such as estuaries, feed more on polychaetes, crustaceans, and bivalves. This adaptability in diet and foraging strategy allows American eels to thrive.