Farming one of the ocean’s greatest fish

DURING May and June, when the mighty bluefin tuna returns to the Mediterranean to spawn, fishermen arrive from all over the world to catch it (click here to watch a video). In days gone by, the fish were netted and killed on the spot. Now, in high-tech operations involving divers and video cameras, they are transferred from the nets into “farms”—arrays of cages anchored to the sea floor from Spain to Malta, to be fattened up. Then, come October, they are sold to Japanese boats, killed, frozen and shipped to Japan.

It is a lucrative arrangement. Anthony Grupetta, the director general of agriculture and fisheries regulation in Malta, says that in those few months most farmers can increase the weight of a wild-caught bluefin by 27-30%. (He claims the Maltese farms do better than this, but does not say exactly how much better.) The cages do not cost much, and the fish fed to a tuna are worth a lot less than the added kilos of tuna-meat that result. What is more, Japanese buyers prefer fish raised this way. They say the quality of the meat from a bluefin killed straight after being caught is less tasty, as the fish has been stressed. …