Short-finned Eel

Fascinating facts about the Short-finned Eel

• A 2021 tracking study showed a short-finned eel swimming 2,620 km (1,630 mi) up the east coast of Australia to the Coral Sea.
• When they finally mature, females can live up to 24 years and grow as large as 1.1 m (3 ft 7 in) and 3 kg (6.6 lb), while males usually stop growing at a smaller size after about 14 years. Their long lifespan and late maturity mean each generation is precious, making population recovery slow if numbers drop.
• Eels only decide their sex after reaching about 30 cm (12 in); in crowded habitats they become males, but in sparse, upstream waters they turn female. This size-dependent sex change shows how population density directly shapes the breeding pool, linking ecology to reproductive strategy.
• Glass eels, the transparent larval stage, drift on the South Equatorial Current for up to four thousand kilometres before arriving at coastal estuaries, where they must find fresh water to grow. Their dependence on vast ocean currents connects distant marine ecosystems with inland freshwater habitats.
• For over 7,000 years, the Gunditjmara people farmed short-finned eels in wetlands created by volcanic lava flows, a practice that supplied food long before modern aquaculture. This ancient stewardship demonstrates that sustainable eel harvesting is possible when human culture works with the species’ life cycle.

At a glance

About the Short-finned Eel

The short-finned eel (Anguilla australis) glides through the lowland rivers, lakes and dams of south-eastern Australia and New Zealand with a body that is long, tubular and snakelike, its dorsal and anal fins mirroring each other in length. Adults typically reach about 90 cm, with the largest females growing to 1.1 m and weighing up to 3 kg, their skin a deep olive-green that can shift to golden or even yellowish tones, while the pale, often silvery underside and green-tinged fins give them a ghostly profile when they turn into the translucent “glass eels” that drift from the sea. These catadromous predators lie in wait, ambushing crustaceans, fish, frogs, snakes, and occasionally waterbirds or rakali, then, after years of freshwater residence, they cease feeding and embark on a monumental migration, up to four thousand kilometres, to spawning grounds near New Caledonia, Vanuatu and Fiji. A striking trait is their ability to absorb oxygen through the skin, allowing them to wriggle over moist ground during upstream climbs, a feat that underscores their evolutionary mastery of both water and land. Their life story unfolds over decades: males mature in about 14 years, females in 18-24, and at roughly 30 cm they undergo a sex change driven by population density, a subtle dance of biology that shapes the gender balance of each river system.

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