The American eel ( Anguilla rostrata ) is a fascinating and ecologically significant fish species found along the eastern coast of North America. Its diet, varying across its life stages and habitats, plays a crucial role in the ecosystems it inhabits. This article delves into the dietary habits of the American eel, exploring what it eats, how its diet changes throughout its life, and the ecological implications of its feeding behavior.
American Eel: Morphology and Distribution
The American eel is a facultative catadromous fish, meaning it spends most of its life in freshwater but migrates to saltwater to spawn. This eel has a slender, snake-like body covered with a mucus layer, making it appear smooth despite having minute scales. A long dorsal fin runs continuously with the caudal and anal fins. Coloration varies, ranging from olive green and brown to greenish-yellow, with a lighter belly.
These eels are found in a wide range of habitats, including streams, rivers, muddy or silt-bottomed lakes, oceanic waters, coastal bays, and estuaries. Their distribution spans the eastern North Atlantic Ocean coastline from Venezuela to Greenland, including Iceland, and extends into the Great Lakes, Mississippi, and Gulf basins.
Feeding Habits and Diet
American eels are primarily nocturnal feeders, relying on their keen sense of smell to locate food. As generalist species, they colonize a wide range of habitats, resulting in a diverse diet that includes most aquatic animals sharing their environment.
Diet Composition
The American eel consumes various items, including:
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- Worms
- Small fish
- Clams and other mollusks
- Crustaceans (e.g., soft-shelled crabs)
- Macroinvertebrate insects
Their diet also includes dead fish and frogs. The stage of maturity influences the diet, with elvers also consuming dead animal matter. American eels use their hinged jaws to remove pieces of food.
Dietary Changes Through Life Stages
The diet of the American eel varies significantly across its different life stages:
- Leptocephali: Little is known about the food habits of leptocephali. Some studies suggest they may be unable to feed initially, while others indicate feeding at later stages.
- Glass Eels: Based on laboratory experiments on European glass eels, it has been reported that they were morphologically and physiologically unable to feed. However, elvers at a later stage of pigmentation, were found to be feeding.
- Yellow Eels: Yellow eels are essentially nocturnal benthic omnivores. Their diet includes fishes, mollusks, bivalves, crustaceans, insect larvae, surface-dwelling insects, worms, frogs, and plants. They prefer small prey animals that are easy to attack. Food type varies with body size, with smaller eels (<40 cm) mainly consuming aquatic insect larvae and larger eels feeding predominantly on fishes and crayfishes. The eel diet adapts to seasonal changes and the immediate environment.
Diet in Specific Habitats
A study in Hannacroix Creek, a tributary of the Hudson River, revealed that eel diets varied among size classes and between day and night feeding periods. Mayfly nymphs were the major prey consumed in each period by all size classes. Nocturnal diet and nocturnal invertebrate samples were similar, indicating a preference for bottom feeding during the night.
Feeding Techniques
Green moray eels, a related species, are nocturnal and use a lie-and-wait method for capturing prey. In aquariums, they are often target-fed using PVC pipes to mimic their natural hunting behavior. Freshwater American eels in aquariums receive a mix of smelt and earthworms to replicate their wild diet.
Ecological Role
The American eel plays a crucial role in its ecosystems. As voracious predators, they help maintain ecological balance by controlling the populations of their prey species. They feed on insects, fish, fish eggs, crabs, worms, clams, and frogs.
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Importance to Other Species
The American eel also serves as a host for the Eastern Elliptio mussel ( Elliptio complanata ), which is important for keeping waters clean through its water filtering capacity.
Threats and Conservation
American eels face several threats, including habitat alteration, climate change, the construction of dams and turbines, and overfishing. Dams block their migrations, and habitat deterioration reduces food availability.
Conservation Efforts
Efforts have been made to improve fish passage across hydroelectric dams. The Canadian province of Ontario has cancelled the commercial fishing quota, and the sport fishery has been closed.
Economic Importance
The American eel is of major economic importance in various areas. They are used as bait for fishing and are considered a delicacy in some regions. Elvers are also eaten live in Europe.
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