American Eel
Anguilla rostrata
New Zealand Longfin Eel
Anguilla dieffenbachii
About
New Zealand's largest freshwater eel spends most of its long life hidden in lakes and rivers, then makes one final journey to the sea to breed and die. It is found nowhere else in the world.
Also known as: longfin eel
How to tell it apart
Divers may confuse it with the shortfin eel, which shares the same rivers. Check where the long dorsal fin begins: on this species it starts well ahead of the fin on the underside, while on the shortfin eel the two fins are close to equal in length.
Appearance
This eel has the classic long, snake-like body of freshwater eels, with dark, smooth-looking skin that wrinkles into folds along the inside of each bend. Its mouth is large, and the dorsal fin running along its back is far longer than the fin on its underside. Females grow much larger than males.
Habitat
It lives in lakes and rivers across New Zealand, including the Chatham Islands, and can turn up far inland in waterways connected to the sea. Young eels prefer shallow, fast-flowing riffles with a coarse, stony bottom, while adults settle next to large debris or under undercut river banks.
Behaviour
This eel matures in fresh water, then migrates to the sea just once, near the end of its life, to breed. After spawning in deep tropical water, the adults die, and their larvae drift on ocean currents for many months before returning to New Zealand as young eels. As juveniles, they can climb wet rock faces and dam walls to reach lakes and rivers far inland.
Diet
It eats insect larvae such as dragonfly nymphs when small, and adds snails, small fish, and yearling trout to its diet as it grows. Large eels have even been reported taking ducklings.
Conservation
New Zealand's Department of Conservation lists this eel as declining, citing shrinking habitat and reduced numbers of mature adults. It breeds only once in its life, which leaves it vulnerable, yet it remains legal to catch, including for use in pet food and traditional fishing.
Did you know?
Maori communities have long tracked this eel, known as orea, timing their catches to its seasonal migrations up and down New Zealand's rivers.
Log it in Into the Blue
Describe what you saw and we name it, then keep every species you find in your Oceandex.
