eels

Eels are elongated fish in the order Anguilliformes. Freshwater eels belong to the family Anguillidae, with several species in the genus Anguilla, including the European eel (Anguilla anguilla) and the American eel (Anguilla rostrata). Other eels, such as morays (family Muraenidae), are also members of Anguilliformes but typically have different habitats and life histories.

Physiology and appearance: Eels have slender, snake-like bodies with a continuous dorsal, anal, and caudal fin. Pelvic fins are absent or reduced, and the skin is usually smooth and scaleless or with tiny embedded scales, often coated in mucus. Eyes and mouthparts vary by species, reflecting their diverse diets. Their elongated bodies and undulating movements enable effective navigation through crevices, rivers, and coastal habitats.

Habitat and life cycle: Eels inhabit a wide range of environments, from open oceans to rivers and lakes. Many freshwater eels are catadromous: they live as juveniles in freshwater and migrate to the sea to spawn. For Anguilla species, spawning is believed to occur in distant offshore waters, with larvae called leptocephali drifting toward continental margins. Leptocephali metamorphose into glass eels, then become yellow eels in freshwater, and later migrate back to the sea to reproduce. In many species, adults die after spawning (semelparity), and detailed aspects of their reproduction remain subjects of study.

Ecology and human interaction: Eels are opportunistic predators and scavengers, feeding on fish, crustaceans, and invertebrates. They have long been valued as a seafood resource, supporting fisheries and aquaculture. Populations are affected by habitat loss, barriers to migration (such as dams), and overfishing, prompting conservation and management measures in various regions.