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Fish farms innovate to meet Japan’s demand for bluefin tuna

To fans of Japan’s natural beauty, the subtropical island of Amami Oshima is among the nation’s brightest jewels: a Unesco World Heritage site, south-west of the mainland in the sea between Kyushu and Okinawa, where ancient beaches merge with dense mangrove forests.

But, for the past 35 years, the tiny archipelago has also been a testing ground of one of the most complex, frustrating and ambitious sustainability challenges in food production: the quest to produce egg-to-harvest Pacific Bluefin tuna on a grand commercial scale.

The mission involves two distinct sustainability problems, both facets of the same fundamental issue that the fish itself is delicious, and that human appetites threaten its long-term survival. Overseas imports to meet Japan’s demand for fish have a large carbon footprint, but the main alternative — domestic fish farms — requires vast quantities of fishmeal, which also presents sustainability problems.

These problems, and the possible solution, have been years in the making. Japan’s diet evolved dramatically from the 1970s as the country underwent its “economic miracle” growth phase and a large, wealthy and consumerist middle class emerged.

Japan’s historic reliance on fish as a key source of protein was transformed, by wealth and global economic reach, into a national obsession with acquiring the finest seafood on Earth. Over time, and with the powerful Japanese trading houses as arch facilitators, imports of fish and seafood occupied an ever greater proportion of the total eaten in Japan — it currently stands at around 40 per cent. Among the world’s top nations by GDP, Japan remains the highest per-capita fish and seafood consumer.

All the associated CO₂ emissions from the large volume of imports could be reduced if Japan switched more of its consumption to domestically farmed fish. But the problem, according to one of the country’s largest fishery companies, Maruha Nichiro, is that Japanese fish farming in its current form requires between 2.5kg and 3.5kg of fishmeal to produce every 1kg of aquacultured fish, which is inefficient compared to fish farming elsewhere.

In Norway, for instance, known for salmon breeding, 1kg of fishmeal produces 1kg of salmon, says Tsutomu Watanabe, who oversees fish breeding at Maruha.

“We need more research and development for breeding that not only requires less fishmeal, but also makes the fish less susceptible to getting sick and gives more meat from the body,” says Watanabe. That fishmeal would ideally be replaced with feed based on soyabeans or corn.

Within its broad love of fish, Japan’s taste for the prized Pacific Bluefin — a key ingredient in sushi and sashimi cuisines — has been especially voracious. It has caused the fish’s natural population to shrink significantly and for the species to appear on the International Union for Conservation of Nature’s “red list” of near threatened species.

As that decline has deepened, it has raised the question of whether Japan’s love of bluefin is sustainable — and whether it could be made so by mastering the notoriously difficult task of farming tuna through a complete lifecycle in captivity.

The first private company to throw serious resources into the project was Maruha. Others have made progress, though not to this scale. One is Toyota Tsusho, the trading arm of the Japanese carmaker, which started working with Kindai University in 2010 to develop fully farmed bluefin tuna and began exporting in 2017.

Maruha, which recognised the looming sustainability issues years ago and set aside the facility in Amami Oshima to address the task, began working on the development of a tuna farm in 1987, but abandoned the project a decade later after persistent failure.

A separate breakthrough at Kindai University in 2002 prompted Maruha to resume its efforts after a near decade hiatus in 2006, though this time with the co-operation of six academic institutions in what had in effect become a national effort.

Difficulties centred on the extreme fragility and environmental sensitivity of the newly fertilised bluefin eggs, the high mortality of larvae, and the non-negotiability of their diet. Little by little, and through years of trial and error, the techniques were improved and ever larger batches were brought from eggs to the three-and-a-half-year age where they can be eaten.

By 2015, Maruha’s two farms in Amami Oshima were able to make the company’s first commercially viable shipment to the sushi chefs of Japan, and by 2019, they were producing enough to sell captivity-reared bluefin to Europe.

In the financial year from April 2020 to March 2021, Maruha produced 500 tonnes of bluefin in a closed-cycle environment, but that only covers up to 15 per cent of its overall sales of the fish. The company’s goal is for all of its bluefin to be from closed-cycle farms.

However, as the absolute level of fully-farmed bluefin production rises, so too does the potency of the second sustainability challenge. It takes three and a half years for farmed bluefin to reach the table, and they not only consume a huge amount of feed, but are currently limited to a diet that is reliant on wild fish.

To make the operation more sustainable, says Maruha, research needs to focus on finding a way to rear bluefin on alternative plant-based proteins, keeping the fish healthy but also maintaining their flavour.