DNA solves century-old mystery about New Zealand’s only extinct freshwater fish

In 1923 Te Rangi Hiroa (Sir Peter Buck) documented last confirmed capture special fish – upokororo or New Zealand grayling.

More than two decades later, upokororo received full state protection, but it was too late. No further sightings have been confirmed. In 1986, upokororo was officially listed as extinct.

Upokororo disappeared so quickly that it is almost unknown to Western science. But nearly a century after the last living upokororo was spotted, we’re now using ancient DNA to finally provide some answers.

Ours research shows the ancient origin of the upokororo, dating back 15 to 23 million years, and its relationship to its Australian cousins.

From fertilizer to phantom

Historical accounts show that the upokororo was once very common in rivers throughout the country. In the 1800s, furies were caught and sold for use as fertilizer and food.

But then it disappeared, probably as a result of a combination of factors — pollution, overfishing, disease and predation by introduced trout.

Despite its abundance in the past, only a small handful of preserved upokororo still exist in museums today. This is one of the reasons why we know so little about this curious fish.

The second reason is that many of these specimens have been treated with formaldehyde, a chemical that preserves the shape of fish but destroys their DNA.

Fish limits

DNA from samples “fixed” with chemicals such as formaldehyde breaks up into small pieces and clumps together. Over time, DNA becomes more and more damaged.

This is a big problem for researchers who want to study species like the upokororo, and the main reason why the extinct fish is understudied compared to other extinct species.

fortunately new methods have recently been developed that help isolate and analyze small damaged DNA fragments. That means genetic analysis of many wet-preserved specimens, such as upakororo, is now possible for the first time.

Such genetic information can provide new insights into parentage and identity extinct species.

Whakapapa with upokororo

Based on the general appearance of the upokororo, scientists have generally considered it to be a close relative of the Australian grayling. The Australian grayling is part of a family of fish that includes the Stoke’s smelt and the New Zealand smelt, which are still found in the Aotearoa rivers.

New DNA data has confirmed that the Australian grayling is the upakororo’s closest living relative, but only a distant relative at best. Genetic comparisons have shown common ancestor of the two species lived more than 15 million years ago.

The ancient origin of the upokororo agrees well with the discovery fossil ear bones of grayling in lake sediments from St Batan in Central Otago.

Genetic and fossil evidence suggests that Upakoraro ancestors arrived in Aotearoa after the Alpine Fault. Until then, modern Aotearoa was mostly under the ocean during the height of the Oligocene.”drowning“27-22 million years ago.

While the child upokororo could live in salt water, adults need brackish or fresh water. The emergence of aotearoa from beneath the wave would create new habitats for the upakoraro.

Return from the edge?

Some scientists have previously put forward a controversial opinion. Can Australian grayling be released into New Zealand rivers to fill the ecological gap left by the extinction of the upokoraro?

This probably won’t be a good plan. Millions of years of independent evolution mean that the niches occupied by Australian grayling and upakororo were probably very different.

If we can’t replace the upokororo, is it possible that they are still somewhere in a remote waterway waiting to be rediscovered? This would not be unprecedented. The Takahē were thought to have died out earlier than a small population rediscovered in the Murchison Mountains in 1948.

Genetic data provide a new tool in the search for survivors. Environmental DNA in water samples from remote catchments can now be routinely compared with known DNA from upokororo. Perhaps one day this will lead to a positive match revealing the whereabouts of the survivors.

Fish populations are declining dramatically around the world. Lessons learned from past extinctions, such as the upokororo, can help save us a fish species for future generations. I hope we can heed the lessons of the past.

This article is reprinted from Conversation under a Creative Commons license. To read original article.