In addition, the skin of Pacific bluefin is delicate and human contact can be fatal, he said; the farmed fish are susceptible to viral diseases such as iridoviruses, which can damage their spleen; at an early stage of their development they are prone to devour any food in reach, including one another; and if they are disturbed by external factors, such as loud noises, they have a tendency to go into a potentially fatal hyperactive “speed burst,” in which they may swim into the pool walls and break their own necks.

The challenges are reflected in the history of the fish in Mr. Mushiake’s Nagasaki pools, the survivors — so far — of a batch of two-year-olds brought in from the Amami-Oshima Island facility.

Originally numbering 200, the Amami-Oshima fish died by dozens en route to Nagasaki — many at the start, when researchers tried to catch them for the journey. Just 127 arrived alive. Since May, almost 40 more have died, leaving only 89.

What happens next remains uncertain. “We first need to gauge if the fish will successfully lay eggs,” Mr. Mushiake said.

Still, if all goes well, he said, the surviving fish in the tank should start reproducing by around June 2015.

At that point, the numbers game gets interesting. A large female Pacific bluefin produces tens of millions of eggs but on average, even in a protected farm environment, only 0.2 percent to 0.3 percent of fertilized eggs will survive the first three months to grow into 30-centimeter fish; and fewer than 0.1 percent will survive to full adulthood. If high-technology methods can significantly raise the survival rate, the commercial consequences will be considerable.

Mr. Mushiake and his team — six marine biologists, including himself, in Nagasaki and another six on Amami-Oshima Island — are trying to do just that.