anguilliforms

Anguilliforms are eel-like fishes characterized by elongated, slender bodies and a distinctive propulsion style in which waves travel along much of the body length, enabling traversal through crevices and complex habitats. The term commonly refers to true eels of the order Anguilliformes, a group within the superorder Elopomorpha of ray-finned fishes.

Morphology and locomotion are tightly linked in anguilliforms. They typically have elongated, cylindrical bodies with dorsal and anal fins often merged into a continuous fin around the tail, and most lack paired fins or have only small pectoral fins. Scales are either absent or very small, contributing to their smooth, eel-like appearance. Their movement depends on undulating waves that pass the entire body, a form of locomotion known as anguilliform swimming, which provides flexibility in confined spaces.

Habitat, distribution, and life history vary across species. Anguilliforms inhabit a range of marine and freshwater environments, from open seas to rivers and coastal estuaries. A notable life-history pattern among many eels is catadromy: adults often live in freshwater or coastal zones and migrate to the ocean to spawn, with juveniles (including leptocephalus larvae and later glass eels or elvers) returning to freshwater. The leptocephalus larval stage is a distinctive feature of many anguilliformes, contributing to their long-distance dispersal.

Taxonomically, Anguilliformes includes several families such as Anguillidae (freshwater eels), Muraenidae (moray eels), Congridae (conger eels), and Ophichthidae (worm eels). Some eel-like fishes outside this order may share anguilliform locomotion but are not true eels.

Conservation and ecology: eel populations are influenced by fishing pressure, habitat loss, and barriers to migration, with some species facing declines in recent decades.