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A researcher examines one of the tanks in which tuna are being raised at the campus of Tokai University School of Marine Science and Technology in Shimizu Ward, Shizuoka. (Mainichi)

SHIZUOKA -- A university professor has teamed up with a technological development company in Shizuoka Prefecture to develop technology that can artificially raise tuna in land-based water tanks.

Unlike sea-based tanks, fish raised in land-based containers are unaffected by red tide. Such a method of raising tuna is extremely rare and environment-friendly.

In the ongoing experiment, one tuna has grown to nearly 9 kilograms, and those involved in the research are aiming to sell the tuna they are raising in several years time.

The research is being conducted jointly by professor Nobuhiko Akiyama of Tokai University School of Marine Science and Technology and WHA, a technological development company based in Yaizu, Shizuoka Prefecture.

"There are moves to restrict tuna fishing, so our aim it to raise tuna from eggs," the WHA president said.

As part of the project, researchers have been raising bluefin tuna for three years in four cylindrical water tanks, each measuring about 5 meters in diameter and about 1 meter deep, placed at the faculty's campus in Shimizu Ward, Shizuoka.

Subterranean seawater pumped up from the ground about 30 meters deep is used in the tanks. Bacillus struggles to grow in such water and the temperature remains stable between 17 and 20 degrees Celsius.

Tuna constantly swim around in order to take in oxygen and could jump out of the tanks in reaction to light, Akiyama says. To prevent such an incident, materials that tuna dislike have been attached to the inner walls of the containers and double-layered curtains have been placed at the entrance to the room housing the tanks to block out light.

One of the tuna weighed 8.9 kilograms as of last month. Researchers killed it and examined its body to find that it had grown enough to be marketed.

Larger tanks will be built at the facility to raise the fish to around 30 kilograms so that they can be sold for a profit.