New Zealand Longfin Eel

Fascinating facts about the New Zealand Longfin Eel

• A female longfin eel can grow to 156 cm and live up to 60 years, dwarfing the 73 cm, 23-year-old males, a size gap that shows how dramatically the species’ life history splits by sex.
• Juvenile elvers under 12 cm can climb near-vertical surfaces up to 43 m tall, using surface tension and friction to travel as far as 130 km inland in a single summer, proving they are nature’s miniature mountaineers.
• Each female releases between 1 million and 20 million eggs that drift for up to 15 months across ocean currents before becoming glass eels, highlighting a reproductive strategy that spans continents and generations.
• Longfin eels grow only 1–2 cm per year, the slowest rate recorded for any eel, so a 106-year-old female can weigh as much as 24 kg, illustrating how patience is built into their biology.
• Despite being classified as Endangered, commercial fisheries still harvest over 100 tonnes annually, revealing a stark conflict between legal exploitation and the species’ precarious future.

At a glance

About the New Zealand Longfin Eel

The New Zealand longfin eel (Anguilla dieffenbachii) is instantly recognizable by its unusually long dorsal fin, which stretches about two-thirds of the body and begins well forward of the anal fin. Its loose skin ripples into distinct wrinkles whenever the eel bends, a contrast to the smooth-skinned shortfin eel that shares its waters. Females dwarf the males, reaching up to 156 cm and living as long as 60 years, while males average 66.6 cm and live 12–35 years. These eels are master climbers as elvers, scaling near-vertical surfaces up to 43 m tall and traveling as far as 130 km inland during a single summer, allowing them to colonise streams and high-country lakes up to 361 km from the sea. Their diet shifts with size: tiny larvae feast on dragonfly nymphs, then add Lymnaea snails, galaxiid fish, upland bully and even yearling trout, while some reports note opportunistic attacks on ducklings. A single female can lay between 1 and 20 million eggs in the deep tropical waters of the western South Pacific, after a multi-thousand-kilometre migration that ends in death. The resulting leptocephalus larvae drift for up to 15 months before metamorphosing into transparent glass eels that enter New Zealand estuaries, grow into coloured elvers, and begin the epic upstream journey that defines their catadromous life cycle.

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