By Bonnie Waycott
Yoshifumi Sawada looks at his Pacific bluefin tuna with pride as his colleague feeds them. “Look, they’re hungry,” he says as the tuna glide to the surface, gobbling up the huge pellets thrown at them. At first glance, this looks like any other fish farm but it’s actually Kinki University’s Fisheries Laboratory, the first in the world to cultivate completely farm-raised bluefin tuna and aiming to produce a stable supply to help address the problem of declining tuna stocks.
Koichi Seko, the first president of Kinki University, founded the laboratory in 1948 beginning with a seaside research facility in the town of Shirahama in Wakayama Prefecture. “Cultivate the seas” were his words and they marked the start of Kinki University’s aquaculture research. In 1970 bluefin tuna farming began. The laboratory started by catching small juveniles off the coast of Wakayama Prefecture using set nets but this was difficult as bluefin have delicate scales and bruise easily, and their gills take in little oxygen so they swim continuously to breathe. Many juveniles didn’t survive in the set nets so the laboratory soon turned to fishing, and in 2002 succeeded in the complete farming of bluefin tuna.
“In June 1979, fish that had been reared since 1974 began to spawn. That was the first spawning in captivity and it continued until 1983 but afterwards there was no spawning for 11 years,” explained Professor Keitaro Kato, deputy head of the Laboratory’s Shirahama station, during a tour of the Laboratory. “In 2012 however, we produced 70,000-80,000 young fish.”
The laboratory’s method is what’s known as full-cycle aquaculture, which involves raising artificially hatched larvae to adults, collecting their eggs and hatching them to create subsequent egg-laying generations.
Kinki’s lab produces 50,000-100,000 juveniles and 80-100 tons of edible tuna a year. The broodstock are raised for at least three years until they are around 1.5 meters long and weigh 80 kilograms. Their fertilized eggs are then collected from the surface of the water (one female lays several million eggs, each about 1 millimeter in diameter), and the eggs then hatch into larvae in about 32 hours.
The larvae are then reared in tanks on land until they are around 6-7 centimeters long and grow into fry in about 40 days, after which they are transferred to ocean net cages. Around 10-15 such enclosures are used, at 10 meters deep with diameters of 20-40 meters.
“Circular cages have more space and are much better suited to bluefin tuna that swim all the time,” Professor Yoshifumi Sawada, director of the laboratory’s Oshima experiment station, told Fish Farming International. “The fish collide with the walls and are difficult to rear in land-based tanks. Land-based operations also incur huge maintenance and electricity costs, so all our farming is done at sea except for the hatcheries.”
Fry that are 52-53 days old after hatching are reared in cages underneath lighting in the center to prevent collisions at night. “Juveniles have a less developed sense of vision and without light, their survival rate decreases drastically,” Sawada and Kato explained.
About three months after hatching, the fish reach around 30 centimeters long and weigh approximately 300 grams. It takes them about two years to grow to over 1 meter long and weigh 20 kilograms, at which point they are ready to be sent to market.
One key issue for the laboratory to ensure that its operations are sustainable is to replace fishmeal feed with plant protein. Sawada believes that soybean, corn meal and sugar cane are all hopeful alternatives. To this end, the laboratory has started an alternative feed project named the “Green Tuna Project.”
“Newly-hatched larvae eat rotifer, and artificially formulated diets are introduced in the late larval period and early juvenile stages,” says Sawada. “As they grow, it’s possible to address the issue of feed in two ways. The first is to develop plant protein feed, and the other is to find a good alternative that can be digested more effectively than fish protein.”
Each tuna at the laboratory must eat 10-15 kilograms of fish for every 1 kilogram of its body weight so when it comes to feed, costs are high. “Our fish are given special diets consisting of fishmeal, fish oil, vitamins and minerals 2 times a day, 6 days a week. At the age of 2 they are fed skipjack mackerel but the use of fishmeal is a problem when it comes to cost, so we are conducting research into developing a plant-based protein,” explaines Sawada. The laboratory examines the quality of the tuna and gives less or more fatty fish accordingly. “Mackerel is good for large tuna as it’s rich in protein and oils, and doesn’t cost much,” Sawada adds. “However, the recent rise in human mackerel consumption in the Far East has been pushing up the price.”
Disease at the laboratory is minimal and efforts are underway to prevent outbreaks by cleaning nets, maintaining an appropriate stocking density, disinfecting sea water in the land-based hatchery and maintaining fish health through suitable nutrition. “We also use vaccinations for any viral diseases, and regularly disinfect the seawater that goes into the land-based tanks,” Kato adds. “Water exchange rates in the ocean and efforts to minimize feeding make our aquaculture operations environmentally friendly,” he said.
“Thanks to our control over all processes of the bluefin tuna lifecycle, we can offer a stable supply of tuna without depending on fish stocks in the wild” Keitaro Kato, deputy head of Kinki University’s Shirahama station
The production and sale of artificially hatched and raised tuna also reduces fishing pressure on natural tuna stocks and contributes to their conservation, says Sawada. “Thanks to our control over all processes of the bluefin tuna lifecycle, we can offer a stable supply of tuna without depending on fish stocks in the wild,” he adds.
Restaurants funding research
Kinki’s laboratory is exploring other channels to expand sales and cultivation opportunities. Today, in addition to shipping its tuna to the United States, it operates restaurants in Tokyo and Osaka, serving the fish it raises and using the profits to fund further research and development. Sawada is also hopeful that the laboratory will continue to sell fingerlings to grow-out farms. “At the moment we don’t have any plans to increase sales of market-sized fish,” he says, “but we do intend to increase fingerling production.”
Floating deaths, sinking deaths: Overcoming bluefin’s challenges
Still, the laboratory isn’t without challenges. Assistant Professor Yasuo Agawa of the Oshima Experiment Station explained to Fish Farming International that bluefin tuna are notoriously difficult to breed in captivity. “Tuna maturation is still extremely hard as it’s difficult to control areas such as oxygen and temperature. In some years the fish don’t spawn and we have yet to figure out why,” he said. In captivity, the participation of females in reproduction is 20 percent and it’s hard to farm male-only or female-only groups so DNA research into farming such groups is underway. “We take blood samples from every tuna we harvest and are working on mapping their entire DNA,” Agawa explained. “Soon, it should be possible to isolate the best DNA characters for disease resistance, growth and sex identification.”
Other issues to address include preventing death among the larvae. “What we call floating deaths occur mainly during the day in 1-4 day-old larvae,” Kato explains. “Aeration in land-based tanks creates an upwelling current that traps the larvae at the surface. As a result, they die. Egg quality has a lot to do with this too. The higher the quality, the lower the death rate. What we call sinking deaths occur at night among 3-7 day-old larvae. These have a high body density compared to seawater so their swimming decreases at night, making them sink and die.”
To prevent floating deaths, the laboratory decreases aeration and creates an oil film on the water surface but this inhibits swim bladder inflation in the larvae. As a result, their body density rises and they sink and die. To address sinking deaths, the laboratory conducted an experiment in 2013 and now uses a surface skimmer to remove oil from the water at a particular time. The challenge, Kato explained, is achieving the right balance between adding and removing the oil.
When it comes to sustainability, feed is the main area that must change. “Replacing fishmeal with plant protein is the most realistic way of ensuring the sustainability of tuna farming,” said Sawada. Feed costs are also half the total costs of tuna production, so we need cheaper materials like plant protein to bring costs down.”
“We developed some pellets for the larvae and juveniles using enzyme-treated fishmeal but the fish wouldn’t eat them as the contents had been altered. We had no choice but to use frozen raw fish as feed,” Kato adds. “Unfortunately this type of feed makes the tuna active and difficult to handle. What we must do now is create alternative diets.”
Spreading knowledge to other countries, other species
Despite the challenges, Kinki is concentrating on the future in terms of further cultivation, and working with other species in different countries, in particular with developing nations to contribute to their industrial development. One project involves Panama and the Inter-American Tropical Tuna Commission to develop yellowfin tuna aquaculture in Panama, where yellowfin populations are declining. The laboratory is sharing its technology, conducting rearing experiments there and in Japan, and dispatching graduate students who are then able to obtain employment. The laboratory is also aiming to contribute to the international community in the area of conserving natural tuna resources by conducting research into breeding and collecting biological information.
While the laboratory is striving to continue its research and increase production, it’s also working to share information on its operations with people in Japan. “The image of tuna farming that we project is extremely important,” says Sawada. “There is a need to emphasize areas such as safety and traceability. People are becoming more interested in those so we’re taking steps to make that information public, for example, by including it online. As a result, the number of repeat customers is increasing.”
Does Sawada believe wild bluefin tuna populations will recover?
“We hope they do,” he says. “We don’t want farmed tuna to be the only way for people to get the fish because after all, Japan has a good and long history of fishing. Supplying both wild and farmed tuna to the market — that’s the ideal for Japanese people.”