Anguilliformes

Anguilliformes is an order of ray-finned fishes that encompasses the true eels and their eel-like relatives. Found in marine, estuarine, and freshwater environments worldwide, the group includes numerous families and hundreds of species ranging from small burrowers to large predators.

Morphology and adaptations are characteristic of the group. Anguilliformes are long, slender fishes with bodies adapted for a sinuous, snake-like swimming style. Dorsal, anal, and caudal fins often fuse into a continuous ribbon running along much of the body. They typically lack pelvic fins, and pectoral fins are variable or reduced. Skin is commonly smooth with reduced or embedded scales, and the size and shape of the mouth and eyes vary with habitat and diet. The lateral line system is well developed, reflecting their predatory lifestyle.

Life cycle and development are notable for the leptocephalus larva, a transparent, ribbon-shaped stage that drifts in the plankton. Many anguilliforms are catadromous, migrating from freshwater or coastal habitats to the open ocean to spawn; after spawning, adults typically die. Juveniles return to freshwater as glass eels and elvers before growing into adults.

Taxonomy and diversity include several well-known families, such as Anguillidae (freshwater eels), Muraenidae (moray eels), Congridae (conger eels), and Ophichthidae (snake or worm eels), among others. Genera and species vary widely in size, habitat, and behavior, with some adapted to reef crevices, others to burrowing in soft sediments, and still others to open water.

Ecology and human interactions: Eels are primarily carnivorous, feeding on fish, crustaceans, and invertebrates. Morays are noted for nocturnal predation and, in some species, specialized jaws. Eel fisheries exist in various regions, but populations are influenced by overfishing, habitat loss, migration barriers, and disease in certain areas.