FaunaHub

Eel

FishElongatedMarine & Freshwater

A green moray eel (Gymnothorax funebris) peering out from a wreck.

Green moray eel (Gymnothorax funebris).

Image: National Marine Sanctuaries, Public domain, via Wikimedia Commons (NOAA).

Overview

Eels are elongated, snake-like fish that make up the order Anguilliformes, the "true eels", with hundreds of species including moray eels, conger eels, and the migratory freshwater eels. This page is a group-level overview; the moray eel is used as a familiar reference. Despite their appearance, eels are fish, not reptiles, and most have long, ribbon-like fins running along the body rather than the separate fins of typical fish.

Habitat & Range

Eels occupy a wide range of habitats. Moray and conger eels live in the sea, often hiding in reef crevices and rocky holes, while freshwater eels live in rivers and lakes but migrate to the ocean to breed. Some species move between salt and fresh water across their lives. Habitat and range vary widely by species, so no single description fits all eels.

Diet

Most eels are carnivorous predators. Moray eels ambush fish and invertebrates from their crevices, while freshwater eels take a range of prey including invertebrates and small fish. Many hunt by smell, being most active at night. Diet varies by species; this page describes general feeding ecology rather than husbandry details.

Behavior

Many eels are secretive and nocturnal, sheltering by day in burrows or crevices. Moray eels are often seen with their mouths opening and closing, which mainly pumps water over the gills for breathing rather than signalling aggression. The freshwater eels are famous for extraordinary breeding migrations, travelling long distances to spawn in the open ocean. Behaviour varies greatly across the group.

Human Interaction & Conservation

Eels are caught for food in many cultures and freshwater eels in particular support important fisheries, but several species — including the European and American eels — have declined sharply and are of serious conservation concern, affected by barriers to migration, habitat loss, and other pressures. Moray and other eels can bite defensively if disturbed and should not be handled. Conservation status varies by species and should be verified against current IUCN Red List and government sources.

Appearance & Recognition

Eels have a long, slender, often cylindrical body and typically lack the pelvic fins of most fish; in many species the dorsal, tail, and anal fins merge into a single continuous fin along the body. Moray eels have thick, muscular bodies and a large mouth with sharp teeth, while freshwater eels are more uniformly snake- like. Most eels are scaleless or have tiny embedded scales.

Similar Animals

True eels are ray-finned fish like most others on FaunaHub, but their elongated bodies set them apart. They are sometimes confused with unrelated snake-like animals; the sea snakes, for example, are reptiles, not fish. Other long-bodied fish, such as some catfish and the electric eel (which is not a true eel), can resemble them superficially.

More photos of the eel

A goldentail moray eel among coral.

Goldentail moray eel (Gymnothorax miliaris).

Image: James St. John, CC BY 2.0, via Wikimedia Commons.

Frequently Asked Questions — Eel

Are eels fish or snakes?
Eels are fish, not snakes. Despite their snake-like shape, they breathe with gills, have fins, and belong to the order Anguilliformes. Their elongated body is an adaptation for living in crevices, burrows, and tight spaces.
Why do moray eels open and close their mouths?
Moray eels frequently open and close their mouths to pump water over their gills for breathing, since their gill openings are small. It looks menacing but is usually a normal breathing action rather than a threat — though morays can bite defensively if disturbed.
Are eels endangered?
Some are. Several freshwater eel species, including the European and American eels, have declined significantly and are of conservation concern, while many marine eels are more common. Status varies by species and should be checked against current IUCN and government sources.

Sources and further reading

Authoritative wildlife references used for general educational context. Conservation status should always be verified against current IUCN Red List data. External links open in a new tab.