Bluefin Blues

The closest I've ever been to a live bluefin was at a tuna fattening farm in southern Japan. I stood on the wobbling catwalk while someone shovelled frozen fish into the pen. The sight of a six-foot silver swimming machine emerging from the bottom of the cage, turning on its side and inhaling a dead mackerel is unsettling.

But it should be no surprise that these farms exist. Many tuna stocks are in trouble, and a new report on Mediterranean bluefin suggests they could easily be destroyed.

If you're interested in the rapid development of this kind of aquaculture, where fish are caught at sea, fattened in cages and then sold, there's a new UN-produced report that includes tuna.

But, as I write in The End of the River, fattening farms will eventually be replaced by full-on, egg to adult tuna culture. Researchers from several countries are going flat out to solve problems of broodstock collection, how to get eggs and sperm out of the fish, how to incubate the fertilized eggs, feed the larvae, keep them going round and round, disease-free, until they're big enough to eat. All big challenges, but I expect they'll all be overcome.

I took the photo in Tokyo's Tsukiji market, where frozen tuna are laid out for inspection before they're auctioned off.