The Japanese eat one in ten of the world’s fish, and 80 per cent of the planet’s prized —and critically threatened — Bluefin tuna. Tuna aquaculture pioneered at Kindai University in Japan offers hope for both fish lovers and the fish.
Oshima Experiment Station, Japan — Professor Tokihiko Okada dug his shovel into a bucket of dead mackerel and heaved the fish into a 30-metre net pen suspended in the placid blue waters of the Pacific. When the silver fish splashed into the pen, the surface erupted, sliced by the torpedo-like shapes of farmed Bluefin tuna as they gobbled up the mackerel.
Two years old and already upwards of 20 kg, these particular fish are among the most exclusive finned creatures on the planet. Wild Bluefin tuna stocks are heavily overfished and listed as a threatened species by the IUCN, the International Union for the Conservation of Nature.
Most Bluefin tuna aquaculture involves raising juvenile fish in captivity. This does virtually nothing to reduce the pressure on wild populations since the juvenile fish are caught in the wild and raised in pens. Nevertheless, it is common in Australia and in the Mediterranean, and in parts of Japan.
But the fish in this pen are different. They are the offspring of farm-hatched fish, raised from eggs until they are adults. Since 2002, researchers at Kindai University have raised Pacific Bluefin tuna completely in captivity, the first group in the world to do so. Now, they produce about 80 tons of Bluefin tuna a year. While that’s only a fraction of the roughly 40,000 tons of Bluefin tuna consumed in Japan every year, it’s a start.
The process is called full-cycle aquaculture, and it offers a small ray of hope to sashimi lovers and Pacific Bluefin tuna populations alike. It also offers an opportunity for Norwegian researchers, with their deep experience in aquaculture and the production of specialized fish food, to expand their expertise to work with this most prized of fish.
110,000 adult fish
It’s hard to overestimate the popularity of Bluefin tuna for the Japanese people. Bluefin tuna at auction at the gigantic Tsukiji Fish Market in Tokyo can be sold for hundreds of thousands of US dollars per fish. Indeed, one sushi restaurant chain owner paid a record US$1.8 million for a 222 kg Bluefin tuna during the first of-the-year fish auction at Tsukiji in 2013.
A May 2016 report by the US-based Pew Charitable Trusts estimated that the wild catch of Pacific Bluefin tuna generates more than US$1 billion in end value. That is the value to fishermen plus all the middlemen in the global marketplace.
At the same time, the population of Pacific Bluefin tuna is heavily overfished, which is what led the IUCN to declare the species “vulnerable” and threatened with extinction in November 2014.
“The species is extensively targeted by the fishing industry for the sushi and sashimi markets predominantly in Asia,” the IUCN said when it issued its announcement. “Most of the fish caught are juveniles which have not yet had a chance to reproduce and the population is estimated to have declined by 19 to 33% over the past 22 years.”
Since then, things have only gotten worse. An April 2016 assessment issued by the International Scientific Committee of Tuna and Tuna-like Species in the North Pacific Ocean said that the Pacific population had declined to just 2.6 per cent of its pre-large-scale commercial fishing population.
The committee also estimated that just 110,000 adult Pacific Bluefin tuna remain in all of the Pacific Ocean.
Sushi lovers worldwide
While the Japanese themselves account for 80 per cent of all Bluefin tuna consumption worldwide, the rest of the world is eagerly gobbling up increasing amounts of sushi, too. While sushi doesn’t necessarily involve the consumption of Bluefin tuna, it almost always means fish.
In Norway alone, the sushi market was worth a whopping NOK 790 million in 2014, according to a study conducted in 2015 by the Norwegian Seafood Council. Since sushi first came to Norway on a large scale in 2006, the total market has expanded by 341 per cent, the council’s report said.
And while salmon is an important component in Norwegian sushi, it is also making huge inroads in the Japanese sushi market, the council reported, with salmon exports to Japan in 2014 a record-breaking NOK 1.7 billion. But tuna remains the top choice for Japanese sashimi.
Thirty-two years in the making
Long before tuna numbers had dropped so precipitously, the Japanese government recognized the pressures facing tuna populations. In 1970, politicians gave Kindai University a mandate and some money: find a way to farm Bluefin tuna.
Thirty-two years later, and long after the government funding ran out, the university was able to report its success. The goal, says Professor Okada, has always been to create a sustainable way to produce Bluefin tuna.
“Tuna is one of the most favored fish in Japan, and at the same time, the species is endangered,” Okada, who is vice director of the Aquaculture Technology and Production Center at the university, said. “We are afraid in the near future we will not be able to eat tuna, so we needed to find a sustainable way to produce it.”
Now, says Shukei Masuma, Director of Kindai’s Aquaculture Research Institute, researchers are working to spread their tuna aquaculture technology around the world, because of the anticipated increase in worldwide tuna consumption due to the growing popularity of sushi.
One per cent survival
Professor Okada said that currently, just one per cent of all eggs that are collected from Kindai’s farmed broodstock survive into adulthood. That is an improvement over the early years, but is still extremely low. Improving this survival rate is extremely important and is one of the top goals for the institute, Masuma says.
The Kindai researchers have learned the reasons behind this low survival rate the hard way, through years of experience. While the fish in the wild may look robust, in captivity they are anything but.
In 1994, while researchers were still perfecting the process, they reported starting with 2.64 million fertilized eggs. Only 1872 fish — 0.07 per cent— survived to the end of their time in the first nursery pens. When these juvenile fish were then transferred to small net cages, nearly half died within the first day of their move. Bluefin tuna are powerful swimmers, and the young fish mainly died from crashing into the net siding of their cages.
Spawning was also unpredictable: beginning in 1982, the captive fish didn’t spawn for 10 years. And the fish were also extremely sensitive to changes in light intensity and loud noises.
The Kindai researchers found that young fish, if startled, would swim in panic and die from crashing at high speed into each other. Even the sudden changes in light intensity with the approaching dawn were enough to throw juveniles into a frenzy.
Over the years, they have learned ways to address these and other problems, but they are continuing to refine the process, Professor Okada said.
Live feed important
Then there is the issue of feeding the juvenile fish. One reason salmon aquaculture has been so successful is that young salmon have well-developed digestive systems from a very young age. That means they can eat fish meal, says Yngvar Olsen, a professor of marine biology at NTNU.
Young tuna, however, need to eat live feed. If they don’t get live feed, they can eat each other, something that the Kindai researchers quickly learned. More importantly, they can simply die, or be deformed, says Elin Kjørsvik, an NTNU biology professor who specializes in marine aquiculture and the rearing of larval fish.
“Juvenile production is often the bottleneck,” in farming fish like tuna, halibut and cod, she said.
Researchers at NTNU and SINTEF have been among those pioneering the farming of small zooplankton called copepods that can be fed to hatchling fish like tuna and halibut. There is no connection between the Norwegian researchers and Kindai. Masuma said that the Kindai researchers are actively working to improve the food they feed to the hatchling fish, however.
Moving down the food chain
Above and beyond experimenting with feed for juvenile fish, the Kindai researchers are testing different kinds of fish meal that can be fed to three-month old fish, which weigh roughly 300 grams.
By this time, the stomach of the tuna babies are developed enough so that they can eat fish meal. The Kindai researchers have just completed testing one kind of feed that is made from roughly 40 per cent plant proteins, but they are not yet done with the analysis of the result
The largest tuna, which can be as big as 70 to 100 kg after 4 years, eat whole fish, such as mackerel and squid. The big fish need to eat about 5 per cent of their body weight in fish each day, Okada said.
But even though farmed tuna still have to eat fish as adults, Olsen says that farming tuna and other top ocean predators makes sense in terms of sustainability.
“From a resource point of view, you can feed (farmed) fish food that comes from lower down on the food chain,” Olsen said. “In terms marine resources, it is more sustainable to bring these fish into aquaculture.”
Showcasing farmed fish
In 2013, Kindai University took what many might consider a surprising step: it opened two restaurants where diners can feast on farmed Bluefin tuna and other fish farmed by Kindai. One of the restaurants is in the posh Ginza district of Tokyo, while the other is in Osaka.
The restaurants are a way to showcase the farmed tuna, but they are also way to serve up some of Kindai’s other aquaculture successes, including red sea bream. All told, Kindai has developed 18 different species for aquaculture, says Masuma.
And while Bluefin tuna tend to be most in the media spotlight, the production of red sea bream for Japanese markets is also very important, Masuma said. Here, he says, almost 100 per cent of the farmed red sea bream in Japan have their origins in the stocks provided by Kindai. The secret, he says, is a focused approach to growing the best fish possible.
“We pick the best of the best and keep breeding them,” he said.
Original article byNancy Bazilchuk and Anne Sliper Midling, Gemini Research News Read it here.