Eels are elongated, snake-like fish belonging to the order Anguilliformes, a group containing approximately 800 known species. Their size varies drastically across different families and genera. Eels inhabit a wide range of environments, from deep ocean trenches to freshwater rivers, leading to a remarkable spectrum of body lengths. The smallest species barely reach a few inches, while the largest can span over 13 feet.
The Giants: Record Lengths and Maximum Potential
The largest eel species are found in marine environments. The heaviest is the European Conger Eel (Conger conger), which can reach a maximum recorded length of 3 meters (nearly 10 feet). These predators of the North Atlantic and Mediterranean can weigh up to 110 kg (240 pounds).
While the European Conger Eel is the record holder for weight, other species exceed it in sheer length. The Slender Giant Moray (Strophidon sathete), an Indo-Pacific species, is considered the longest eel in the world, reaching up to 4 meters (13 feet). The Giant Moray (Gymnothorax javanicus) commonly reaches lengths of 3 meters (10 feet) and a weight of 30 kg (66 pounds).
Typical Sizes of Common Eel Species
The lengths of eels most often encountered by people, particularly the freshwater species, are modest. The American Eel (Anguilla rostrata) and European Eel (Anguilla anguilla) generally reach a length of 2 to 4 feet (60 to 120 cm). A distinct difference exists between the sexes, with females growing substantially larger than males.
Female American Eels can reach up to 1.5 meters (5 feet) and weigh over 7 kg (15 pounds), while the males rarely exceed 60 cm (2 feet). Similarly, female European Eels can grow over 1 meter (3.3 feet), but males mature at a much smaller average length of about 30 cm (1 foot). These lengths are for the mature, adult stage before their spawning migration.
At the other end of the size spectrum are specialized groups like the Garden Eels. Species such as the Spotted Garden Eel are small and slender, rarely exceeding 40 cm (16 inches) in total length. They live in colonies, spending their lives partially buried in the sand with only a fraction of their length exposed to the water current.
How Eels Achieve Their Length: Growth and Lifespan
Eels achieve their length through a life cycle involving four distinct metamorphic stages. The journey begins in the ocean with the leptocephalus stage, where the transparent, leaf-shaped larvae drift for months or up to two years, growing to a few inches. They then transform into the glass eel stage, becoming transparent, cylindrical forms that migrate toward coastal waters and estuaries.
Upon entering fresh or brackish water, the glass eels develop pigmentation and become elvers, young eels typically around 8 cm (3 inches) long that actively migrate upstream. The most prolonged stage is the yellow eel phase, where the majority of length is accrued over many years in rivers and lakes. This growth phase can last from 5 to over 20 years, depending on the species, gender, and environmental factors like temperature and food availability.
Once the eel has accumulated sufficient fat reserves and reached sexual maturity, it undergoes a final transformation into the silver eel stage. At this point, the eels stop feeding and growing in length, dedicating their energy reserve to the long-distance migration back to their oceanic spawning grounds. The prolonged duration of the yellow eel stage is the primary reason some eels achieve significant lengths before their terminal spawning migration.