| Elaine Kurtenbach |
TATEYAMA, Japan (AP) – Of all the overfished fish in the seas, luscious, fatty bluefin tuna are among the most threatened. Marine scientist Goro Yamazaki, who is known in this seaside community as “Young Mr Fish”, is working to ensure the species survives.
Yamazaki, 48, is fine-tuning a technology to use mackerel surrogates to spawn the bluefin, a process he hopes will enable fisheries to
raise the huge, torpedo-shaped fish more quickly and at lower cost than conventional aquaculture. The aim is to relieve pressure on wild fish stocks while preserving vital genetic diversity.
His inspiration hit him 15 years ago while he was out at sea during graduate studies at the Tokyo University of Marine Science and Technology, and a school of bluefin tuna streaked by.
“They swam just under the boat, and they were shining metallic blue. A beautiful animal,” Yamazaki said. “Before that, tuna was just an ingredient in sushi or sashimi, but that experience changed bluefin tuna into a wild animal to me.”
An animal, that like so many other species, is endangered due to soaring consumption and aggressive modern harvesting methods that have transformed the bluefin, also known as “honmaguro” and “kuromaguro,” from a delicacy into a commonly available, if pricey, option at any sushi bar.
This month, experts in charge of managing Atlantic bluefin met in Italy and raised the quota for catches of Atlantic bluefin tuna by 20 per cent over three years. Stocks have recovered somewhat after a severe decline over the past two decades as fishermen harvested more to meet soaring demand, especially in Japan.
But virtually in tandem with that, the International Union for Conservation of Nature put Pacific bluefin tuna on its “Red List”, designating it as a species threatened by extinction.
About a quarter of all tuna are consumed by the Japanese, according to the United Nations Food and Agricultural Organization. They gobble up most – between 60 per cent and 80 per cent – of all bluefin. Rosy, fatty “chu-toro” from the upper part of bluefin bellies, is especially prized for sushi and sashimi.
Out at his seaside lab in Tateyama, on the far northern rim of Tokyo Bay, Yamazaki and other researchers are hoping their latest attempt to
get mackerel to spawn bluefin will prove a success. An earlier attempt failed due to what he thinks was a problem with the water temperature.
Yamazaki’s technique involves extracting reproductive stem cells from the discarded guts of tuna shipped by cold delivery from fish farms and inserting them into mackerel fry so tiny they are barely visible.
The baby fish are put in an anesthetic solution and then transferred by dropper onto a slide under the microscope. Researcher Ryosuke Yazawa deftly inserts a minute glass needle into one’s body cavity to demonstrate.
Under the right conditions, the tuna stem cells migrate into the ovaries and testes of the mackerel. The team is now waiting to see if the mackerel, when mature, will spawn tuna, and if the tuna will survive. Following that, they could be released into the sea or farmed.
The research team has already succeeded in using surrogate technology to produce tiger puffer fish, the poisonous “fugu” used in sashimi and hotpot, using smaller grass puffer fish. It has produced trout spawned by salmon. Companies that import rare and tropical fish also are interested in the technology.
The method could help reduce pressure on wild populations, Yamazaki hopes, and also help ensure the greater genetic diversity needed to preserve various species.