Freshwater eels are elongated fish that navigate a unique life cycle, beginning in saltwater and migrating to freshwater environments to mature. They are adaptable predators in aquatic ecosystems. Their diverse diet and hunting methods reflect their opportunistic nature and ability to thrive in various freshwater habitats.
Main Food Sources
Adult freshwater eels are carnivorous, consuming a wide array of prey. Their diet commonly includes smaller fish and molluscs like snails, worms, slugs, and clams.
Crustaceans, such as crayfish, various types of crabs, and shrimp, are a substantial part of their diet. Aquatic insects and their larvae are also an important food source, with specific examples including stonefly, dragonfly, damselfly, soldierfly, and cranefly larvae.
Beyond live prey, freshwater eels also act as scavengers, consuming dead fish when available. They are highly opportunistic, sometimes even leaving the water to feed on terrestrial invertebrates like slugs and worms found in damp fields. Larger eels may also prey on amphibians, such as frogs, and small birds like ducklings.
Dietary Variations
An eel’s diet varies considerably based on its age, size, and the specific environment it inhabits. Younger eels, often referred to as elvers or glass eels, primarily consume smaller invertebrates like insect larvae, worms, and zooplankton. As these eels grow larger, their dietary preferences shift towards more substantial prey.
Larger eels, particularly those exceeding 40 centimeters in length, incorporate more fish and crayfish into their diet. This transition in prey size is a natural progression as the eels mature and are capable of capturing larger organisms. The immediate environment also plays a role, as eels adapt their feeding habits to the seasonal availability of food sources.
During colder months, freshwater eels become less active and may feed very little, often entering a state of dormancy while burrowed in mud. Conversely, they feed more intensely during summer when prey is abundant. Unusual environmental conditions, such as high lake levels, can also influence their diet, leading them to consume terrestrial invertebrates like earthworms and grass-grub larvae that become accessible.
Hunting and Feeding Strategies
Freshwater eels are predominantly nocturnal predators, conducting most of their hunting activity under the cover of darkness. During daylight, they typically remain hidden in shelters like burrows, logs, or dense vegetation. This nocturnal behavior allows them to ambush less active or visible prey at night.
Their hunting relies on a keen sense of smell, their primary tool for locating food in dark or murky waters, as their eyesight is not strong. Eels use ambush tactics, waiting patiently for unsuspecting prey to come within striking distance. Once prey is detected, their elongated, serpentine bodies allow them to move swiftly and silently through the water.
Eels possess small, sharp teeth to grip slippery prey effectively. For larger items, some species use a rotational spinning motion to tear off manageable pieces. Their flexible bodies and ability to consume large meals, stretching their stomachs, contribute to their predatory efficiency. Their slippery, mucous-covered skin and capacity to breathe air for short periods allow them to navigate diverse environments, even crawling over wet land to bypass obstructions or access new feeding grounds.