Study underway to learn more about Guam's native freshwater eels

Study underway to learn more about Guam’s native freshwater eels

Karina Mejia, a graduate student in biology at the University of Guam under the National Science Foundation’s EPSCoR program, and her research mentor, UOG Associate Professor of Biology Daniel Lindstrom, seek to answer some unknowns about the eel Guam’s most common river eel – the giant spotted eel, or marbled eel (Marbled eel) – and they will use innovative techniques and technologies in the process.

Anguilla eels are found widely across the tropics, and their popularity in Japanese, Chinese, South Korean, and Taiwanese cuisine has contributed to the endangerment of four of its 16 species. Although the species in Guam is not endangered, it could be managed sustainably as a food source, but surprisingly little is known about it.

Known and unknown

River eels spend part of their life cycle in saltwater and freshwater. Especially, A.marmorata and related species spawn in the ocean, where the eggs and larvae drift until they become small elvers and enter freshwater rivers.

For the A.marmoratathe spawning grounds are not well defined and it is unclear what time of year they travel upstream – both essential pieces of information for sustainably fishing them in the wild or rearing them in aquaculture facilities.

A deep dive into DNA

Former UOG graduate student Sean Moran discovered that marbled eels from the rivers of Guam have significant genetic differences. Mejia’s main goal, she said, is to build on her findings by showing that there are genetic differences because they come from different spawning grounds.

To do this, she will perform high-resolution DNA analysis using a new PCR-based gene sequencing technology called MIG-seq developed at Tohoku University in Japan. This will allow him to group eels from Guam with other genetically documented eels in the Indo-Pacific.

Rings that tell a life story

The second analysis Mejia and Lindstrom hope to do is a technique known as otolith microchemistry. It is commonly used on species around the world to trace their migration patterns, but it has not yet been conducted on the A.marmorata species in Guam or elsewhere.

The process assesses chemical concentrations in an ear bone, or otolith, of a fish. Just like a tree, otoliths add rings over time, capturing chemicals from their surroundings. The elements found can be compared to the chemical signature of different parts of the ocean, providing a daily timeline of fish migration.

“So we can say, ‘OK, this eel has been floating in the ocean for several days,’ and if we’re lucky, we can say, ‘That’s where it was on day 27 – that’s is really close to where it was spawned,” Lindstrom said. “We hope it’s possible.”

Storage Information

With the lack of research on the tropics Anguilla species, Mejia hopes her work will not only contribute to regional conservation efforts, but also inform local conservation decisions so that Guam’s population is not threatened.

“If we’re able to say, ‘You’re only allowed to catch this much,’ we can sustain the population and prevent it from becoming endangered and then extinct,” she said.

Lindstrom said their findings will also be applicable to aquaculture. No one has been able to spawn and rear these eels or related eels completely in captivity, he said, so eel farms depend on collecting and rearing captive eels. juvenile eels, or glass eels, when they swim in rivers. By knowing where and when spawning occurs, those places could be better protected and wild fisheries could be managed more sustainably.

Mejia hopes to have enough data by next fall to draw conclusions and complete her thesis by spring 2024.

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