Anguilla is the genus of freshwater or catadromous true eels, family Anguillidae, with atlas records spanning Indonesia, the Philippines, Papua New Guinea, Australia, Madagascar, Mozambique, Tanzania, and Samoa — a distribution that reflects the genus's real range across the Atlantic, Indian, and Pacific basins. The 17 species in the atlas run from roughly 23.5 in to a striking 78.5 in, and all share the classic eel body plan: a long, snake-like, scaleless-looking form with a continuous dorsal-anal-caudal fin margin and no pelvic fins. Every species has the same extraordinary life cycle in common — adults live and grow for years in fresh or brackish water, then migrate enormous distances to spawn once in the open ocean and die, their larvae drifting back toward continental waters as leaf-shaped leptocephali before settling into rivers as glass eels.
Anguillid eels are of far more scientific and fisheries interest than aquarium interest: species like Anguilla anguilla (the European eel) and A. japonica (the Japanese eel) underpin major food fisheries and glass-eel aquaculture industries, while A. rostrata (the American eel) and A. dieffenbachii (the New Zealand longfin eel) are important culturally and ecologically in their home rivers. A few species occasionally turn up in the hobby as curiosity pets for very large, long-term tanks, but their size, nocturnal habits, and eventual need to reach the sea make them impractical aquarium subjects. The conservation picture is serious: the atlas tally includes species rated Critically Endangered, Endangered, and Near Threatened, driven by overfishing of the highly prized glass-eel stage, river barriers that block the spawning migration, and habitat loss, and A. anguilla in particular has become one of the most conservation-watched fish species in Europe.
The genus's spawning grounds remained a scientific mystery for centuries; it took decades of research, capped by early-20th-century work tracing progressively smaller larvae back toward the Sargasso Sea, to confirm where Atlantic Anguilla species actually breed, and the precise spawning behavior of the adults has still never been directly observed in the wild.