How Japanese innovation could keep tuna on the menu

Farmed tuna in southern Japan

It is spawning season for one of the first generations of farmed bluefin tuna in southern Japan. After spending about a month at a hatching facility, the baby tuna are now heading to reserves. Some will go to other fish farms in the winter to be fattened for sale in the market, and some will stay on until spring.

As with human babies, the bluefin tuna need to be fed every hour when they are very young. Caretakers arrive at the reserves at dawn and stay until late at night, and, if necessary, they stay throughout...