There is an interesting article about the cultivation of tuna in Japan was released by The Asahi Shimbun as follows:
The supply of tasty bluefin tuna is dwindling, yet demand is as strong as ever. This is the dilemma facing fishermen at sea who recognize the need to conserve precious tuna resources.
On the other hand, researchers on land are also trying to come up with more efficient fish farming techniques. The business opportunities would appear to be endless.
There are various hurdles to overcome, not least finding a way to manage the reproductive process.
But something happened on the evening of May 16, 2014, that may change the entire picture. What researchers in the Taira-machi district of Nagasaki (in Japan) witnessed was a world-first. Located in that neighborhood is the Seikai National Fisheries Research Institute of the Fisheries Research Agency.
Keiichi Mushiake, 57, who heads the Research Center for Tuna Aquaculture at the Nagasaki site, explained what they saw.
"The entire aquarium turned white because it became cloudy from the milt," he said. "We could not see where the tuna was. It looked like a haze had formed."
The phenomenon occurred in an aquarium measuring 20 meters in diameter and 6 meters deep. The aquarium was built to collect fertilized fish eggs.
About 40 artificially-hatched adult bluefin tuna were placed in the aquarium and some spawned. The experiment succeeded with the fertilizing of the eggs by the milt.
"Two or three male tuna went after a female fish and we saw such tailing activity in various places within the aquarium," Mushiake said. "Each tailing would last for about 30 seconds at most. After the fish settled down for a bit, they would then go after other female. That continued to occur for some time."
The spawning activity continued for about three months until the end of August as the males covered milt on the eggs laid by the female. A total of 50 million fertilized eggs were collected from the two aquariums set up for that purpose.
That was the first spawning by bluefin tuna at a facility on land set up to collect eggs.
The facility was completed in June 2013 with the central government contributing 2.1 billion yen (US$17.4 million) to the project. That investment was made because a fertilized egg collection facility on land holds the key to the aquaculture business.
Ordinarily, in raising bluefin tuna on farms in Japan, fry not yet a year old are raised in aquariums for about three years. However, catch restrictions were placed on fry and young fish from January 2015 to prevent overfishing.
That development led to attention turning toward the possibility of complete fish cultivation.
Artificial hatching involves hatching eggs collected from adult fish in the wild. Complete fish cultivation would mean hatching eggs collected from adult fish that themselves were artificially hatched.
If complete fish cultivation can be achieved, there would no longer be the need to go after fry in the wild.
The first successful complete fish cultivation of bluefin tuna occurred in 2002 by researchers at Kinki University Fisheries Laboratory. However, in order for the project to become an established business venture, a major hurdle had to be overcome: controlling the spawning period.
Fry spend their first winter in open-water tanks. To survive the cold winter in a confined tank, the young fish should be at least 3 kilograms. Fish can grow to that size if spawning occurs in April or May, but the bluefin tuna in the tanks spawned in July and August. That meant the fry were only about 1 kg when winter came along, so many ended up dying.
One way to move up the spawning period is to adjust water temperatures. However, that would require a facility on land.
A major problem with such a land-based facility is the huge expense involved, with no assurance that the investment would be recovered. That makes such a facility the largest problem in the tuna cultivation business.
Eggs of bluefin tuna hatch about 24 hours after fertilization.
After the world's first land-based fertilization, about 3 million fertilized eggs were sent to the Amami laboratory of the Fisheries Research Agency on Kakeromajima island in Kagoshima Prefecture and the Nagasaki prefectural government's fisheries testing facility.
It took nine hours to transport the eggs to the Kakeromajima facility, over land, air and sea.
On the receiving end of the delivery was Satoshi Shiozawa, 57, who heads a research group there looking into breeding and multiplying.
"The hatching began as soon as the eggs arrived," he said. "Although bluefin tuna can grow to up to 400 kg, the eggs are only 1 milligram. Feed has to be given two days after hatching. Only 1 percent of the hatched fish reach 5 to 6 centimeters in size."
After raising fry to such size over 30 to 40 days, the fish are placed in open-water tanks. Only one-tenth of those fry grow to 500 grams in about two months. Of that fish, only half further grow to a size at which they can be sold to the market. In other words, only 0.05 percent of the hatched fish ever become big enough for market.
There are any number of ways for the hatched fish to die. Some sink, while others float to the surface but still die. Some die after being eaten by other fry. Even if the fish grow somewhat bigger, they die in a collision caused when something surprises it.
All such hurdles have to be overcome for the fish to become large enough for the market.
Meanwhile, major companies are holding out expectations that the complete fish cultivation cycle will succeed through fertilized egg collection on land.
Maruha Nichiro Corp. resumed research on complete fish cultivation in fiscal 2006 after suspending it temporarily. The company began selling the first batch of tuna raised through complete fish cultivation on June 5.
Akira Ito heads the company's aquaculture operations department.
"The three areas we want to improve on are the survival rate, feed and the type of tuna to raise," he said.
The last issue involves breeding tuna that is the most suited to complete cultivation and that will grow the fastest while maintaining a high survival rate.
Maruha Nichiro is one of the participants in a project on genetic research.
Mitsuru Ototake, 55, heads the Research Center for Aquatic Genomics at the National Research Institute of Fisheries Science, which is located in Yokohama's Kanazawa Ward.
"If we take a sampling of fry soon after birth and check its genetic makeup, we find out, for example, that the fish were spawned by four females," Ototake explained. "When we conduct a further study of the surviving fish 18 days later, we can find out which parent gave birth to the most fry that survived."
The ultimate goal is to determine the DNA sequencing for the fish with the highest survival rate, the fastest growth and the most durability against disease. By cross-breeding tuna with such genetic makeup, it might be possible to produce the "perfect" one for fish cultivation.
Research has already succeeded in freezing milt for preservation. The problem was collecting the eggs. A land-based facility is indispensable for collecting eggs from specific tuna. That is why such high hopes are being placed on the Nagasaki facility.
"The exit for our research will be in understanding what tuna to keep as a candidate for cross-breeding," Ototake said.
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