Juveniles still rely on the sea: the 30-year wall facing a 63-year-old Vietnamese tackling giant mottled eel farming

In the Chau Truc lagoon of Gia Lai province (formerly Binh Dinh province) in central Vietnam, a fish raised by a 63-year-old farmer, Vo Thuan Tu, is drawing attention in local media. In a pond of about 10,000 sq m he ships 4 to 5 tonnes a year of the large eel called giant mottled eel in Japanese (Vietnamese: ca chinh), selling them at 500,000 to 600,000 dong per kg (about 3,000 to 3,600 yen). What made the headline, however, was not "success at full-cycle farming." It was the fact that, even after 30 years, he still cannot get this fish to spawn inside the pond. The structure of relying on the wild for fry (seed stock) mirrors Japan's efforts on Co To Island, which switched squid that had relied on the wild to farming the same wall, reflected in the difficult subject of the eel. For Japanese seafood buyers who handle live fish, this lagoon's story is at once "a promising new supply source" and a textbook of "why the supply does not stabilize."

What was reported: from "hundred-million losses" to a harvest once every six months

In 1997 Mr. Tu joined a project of what was then the Binh Dinh province Department of Science and Technology and began researching giant mottled eel farming. He went independent in 2000 and, sleeping on the lagoon shore, piled up trial and error. According to the local paper, there were years when failures cost him 1 billion dong a year (about 6 million yen).

The turning point was 2010. He succeeded in "acclimatization" (junchi), raising fry bought from the wild to full health in the pond, and it began to turn as a business. He now raises about 10,000 head in four ponds, growing them over 2 to 3 years to a marketable size of 1.5 to 3 kg. Shipments are 4 to 5 tonnes a year of marketable fish and 3 to 4 tonnes a year of seed stock raised for other farmers. He obtained VietGAP certification and OCOP three stars, and in 2018 also received a prime-ministerial commendation as an "outstanding Vietnamese farmer."

Even with success, "you can't get the eggs": the 30-year-unsolved mystery of spawning

What is worth noting here is the distinction that what he reached is "the completion of grow-out (rearing)," not "full-cycle farming." The giant mottled eel grows for several years in rivers and lagoons and, when mature, migrates to the deep sea to spawn. The hatched larvae ride the ocean currents back to the river mouth. No one has yet established the technology to reproduce this migration and spawning behavior in captivity.

Mr. Tu himself tells the local paper this: "No matter how many decades I do it, the seed stock alone I cannot supply myself. I can grow them big, but I cannot get them to spawn in the farming environment." So he still every year, from the 11th to the 2nd month of the lunar calendar, buys wild fry from fishermen on the central coast. Behind VietGAP and OCOP, the region's signboards, a structure continues in which the origin of supply still depends on the sea's bounty.

The same wall as Japan's glass-eel problem

Many readers must feel a strong sense of familiarity at this structure. Japan's eel farming too is a method of catching and raising wild glass eels (juvenile Japanese eels), and the juveniles have been at a low level ever since the 1980s. "Full-cycle farming," in which eels are spawned artificially, the larvae raised to glass eels, grown to adults and spawned again, was first achieved in the world by the Fisheries Research and Education Agency in 2010. But 15 years on, it has not reached commercialization. What forms the wall is the larval feed.

Technology on the Japanese side is advancing steadily. In July 2025, the Fisheries Research and Education Agency and Yanmar jointly developed a new mass-production tank and succeeded in producing about 1,000 glass eels per tank, cutting the rearing cost per seed fish to around 1,800 yen, about one-twentieth of the previous level. Nissui also began joint research on mass-production technology for artificial seed in April that year. It is a stage where national institutions and major companies, banded together for decades, are finally setting about breaking the trial-scale wall. Knowing that difficulty, a single farmer in Gia Lai province not having solved spawning in 30 years comes to look, if anything, natural.

Why Vietnamese giant mottled eel is worth watching anyway

Given that the origin of supply is reliant on the wild, why is this fish interesting as a sourcing target? Laid out, there are three points.

First, the fact that the giant mottled eel is a premium live fish with strong demand in the Chinese-speaking world. It is a large species that can reach 2 m in length and 20 kg in weight, prized in China's Guangdong, Hong Kong and Taiwan as a nourishing and tonic ingredient, with some regarding it as more valuable than the Japanese eel. Being low in fat and firm in flesh, it is choosy about cooking, but having established demand outside the kabayaki cultural sphere also means sales channels other than Japan exist from the start. This is the background to why the region's price is hard to collapse.

Second, Rather than waiting for "the achievement of full-cycle farming," rearing and logistics should be the evaluation axes, is the point. Since the fry are reliant on the wild, the supply volume of Vietnamese giant mottled eel will keep wavering for the time being. So what Japanese buyers should look at is not the newsworthiness of breeding but the water-quality management Mr. Tu established (a method of stabilizing the pond ecosystem with a biological preparation made from molasses, fully ripe bananas and fermented milk) and the traceability guarantees of VietGAP and OCOP. The black tiger shrimp Ca Mau site taking on the creation of a domesticated lineage, as there, value dwells in "reproducible rearing quality" more than in "a breakthrough in the species."

Third, Japan's seed technology itself could become the key to unlocking Vietnamese product's growth margin, is the paradox. If Yanmar's mass-production tanks and the development of cheap larval feed are put into practical use, that technology has room to apply not only to the Japanese eel but also to the closely related giant mottled eel. Vietnam's production bound by wild fry, and Japan with its breeding technology. If raw-material sourcing and technology transfer can be designed as a single deal, the lagoon's 30 years turn into "a starting point for stabilizing Vietnamese supply."

Basic information on the Chau Truc lagoon

Summary: do not swallow the "farming success" headline whole

The story from the Gia Lai lagoon is too good to consume as a stirring success tale. What Mr. Tu showed is the technology to raise wild fry to full size in the pond and the real existence of Vietnamese giant mottled eel as a premium live fish, and at the same time the limit that "the spawning wall cannot be crossed even in an individual's 30 years." This two-sidedness is close to the reality that Japanese sourcing managers handling live fish should grasp. What should be checked first is the shipping price of Vietnamese giant mottled eel for the Chinese-speaking world and whether there is stock for Japan. Next, the rearing quality and traceability of VietGAP- and OCOP-certified farmers. And whether Japan's seed mass-production technology is expanded horizontally to the giant mottled eel. Choosing a supplier with the premise of reliance on the wild factored in the Thanh Hoa case where a former fisherman reached annual revenue of 12 billion dong with three-stage farming also connects to an eye for spotting producers who, small-scale though they are, grow depending on the design.

Sources

• 30 năm đêm thất bại cho thành công với loài cá sinh ở biển lớn trong đầm（Dân Việt / Trang Trại Việt）
• Lão nông 30 năm vẫn chưa giải mã được tập tính sinh sản kỳ lạ của cá chình（Dân trí）
• New eel seed mass-production tank developed, contributing to cutting glass-eel production cost (Yanmar, July 2025)
• Giant mottled eel (Anguilla marmorata) / distribution, food use, demand (Wikipedia)