New Zealand longfin eel

|248x248px The easiest way to identify the longfin eel is by the length of its fins: the dorsal (top) fin is about two-thirds the length of the body and starts significantly further towards the head than the anal (bottom) fin. In the shortfin eel the fins are of similar length. When a longfin eel bends its loose skin wrinkles distinctively inside each bend, where a shortfin eel's skin is smooth. A longfin's mouth extends past its eyes, further than a shortfin's. Determining longfin sex is difficult as their sexual organs are not determined until they are over 45 cm in length. The only method to determine longfin eels sex is through internal examination and it only becomes easy to distinguish when the eels mature and migrate. ==Life cycle==

Like other members of the Anguillidae, longfin eels have a rather unusual life cycle: they grow and mature into fertile adults in fresh water, then migrate to the sea to breed. This catadromous breeding system also ensures randomised mating, creating a panmictic population. The New Zealand longfin eel is a very long-lived fish, with records of females reaching 106 years old and weighing up to 24 kg. They have the slowest growth rate of any eel species studied, just 1–2 centimetres a year. Longfin eels life cycle like other species of Anguillidae eels is rather complex consisting of four distinct life stages which remained a mystery for many decades and still is not fully understood. New Zealand longfins breed only once at the end of their lives, making a journey of thousands of kilometres from New Zealand to their spawning grounds near Tonga. Their eggs (of which each female eel produces between 1 and 20 million This drifting is thought to take up to 15 months. The recruitment of glass eels into New Zealand's freshwater river networks is a very variable process, thought to be affected by the El Niño and La Niña Southern Oscillations. ==Diet==

Longfin eels have an omnivorous diet and are opportunistic feeders. Their diet as small eels largely consists of insect larvae, such as dragonfly nymphs (Procordulia grayi). ==Habitat and distribution==

Anguilla dieffenbachii is endemic species to New Zealand, widely distributed through the country's lakes and rivers, including the Chatham Islands. Longfin eels are often found great distances inland (up to 361 km) along fresh waterways and in high country lakes which are connected to the sea. At this size the elvers can travel up to 130 km inland over a summer, and have been observed climbing near-vertical surfaces up to 43 m tall. Adult longfin eels tend to be found next to or under large pieces of debris and undercut river banks. ==Significance for Māori==

Ōrea are an important traditional food source for Māori, who have long had extensive knowledge of the timing of their upstream and downstream migrations. ==Commercial fishing==

The commercial fishing of longfin eels began to gain momentum in the 1960s, and by the 1970s there was a 2000 tonne yearly catch. Commercial longfin eel fishing was included in the Quota Management System (QMS) in 2000 for the South Island and 2004 for the North Island. This set limits to the minimum and maximum size (220 grams and 4 kg) and the Total Allowable Catch (TAC). The capture and export of glass eels in New Zealand has been prohibited. ==Aquaculture==

There have been a number of attempts at aquaculture of longfin eels. The first were in the 1970s, and did not remain operational for long, with the last farm closing in 1982. ==Conservation==

In 2003 biologist Don Jellyman predicted longfin numbers would drop by between 5 and 30% in the following decade. The DOC panel concluded though that the commercial fishery of the species is stable or increasing, and noted "that public discourse on the longfin eel portrays the species as being severely threatened despite data that indicate otherwise." This conclusion has been seriously questioned, repeatedly, both before and since then, throwing its validity into doubt. In June 2012 it was reported that some pet food companies use the nationally threatened eels in their products, sparking outrage by conservationists. Scientists and conservation groups have growing concern for the survival of the species, as they can be legally killed and have a slow reproduction rate, breeding only once at the end of their lifetime. The 2018 IUCN assessment noted a sharp decline in longfin numbers over the last century, accompanied by significant reduction of habitat. The IUCN currently classes the species as "Endangered", making the following notes: "Population Severely Fragmented; Continued Reduction in Mature Individuals; Continuing Decline in Area/Extent and/or Quality of Habitat" Despite this, the New Zealand government continues to allow its export and allows legal recreational killing of the fish. ==References==