Jane Chen / Shanghai Daily news

A new industry standard on tuna may banish the delicacy from Sashimi menus at nearly all local eateries.
According to the standard, which is expected to take effect next year, China will ban tuna treated with CO, or carbon monoxide gas, from being served as Sashimi, citing the health hazard it poses.  All authorized tuna products will have to carry a freshness authentication logo from the fisheries authority, the Shanghai Morning Post reported.
The report quoted a local tuna expert, Professor Wu Jiale of the Shanghai Fisheries University, as saying yesterday that a study group he heads has finished drafting an industry standard for tuna eaten raw as Sashimi.  The draft, now submitted to the Ministry of Agriculture, is expected to go into effect next year.
It may affect nearly all the restaurants and supermarkets in Shanghai offering tuna Sashimi, industry insiders worried, because most of the tuna on the local market is treated in this way.
As a deep-ocean fish, tuna must be stored fresh at below minus 55 degrees Celsius. But in Shanghai, there are no refrigeration facilities capable of producing such low temperatures.
An indication of the freshness of the fish is its bright red color, which is caused by myoglobin, or the muscle pigment that carries oxygen to working muscles.  When stored for some time and exposed to oxygen, the red color changes to shades of brown.
To retain the red color for longer and make it look fresh, processors treat tuna with CO.
Long-term consumption of such fillets will harm consumer's health, particularly their kidneys, with some being food-poisoned, according to Huang Jinbao, vice president of the China Fisheries Association's ocean fishery branch.
Such cases have occurred in Japan and the United States. To avoid mishaps, Japan has enforced a ban on the sale of CO-treated tuna since the mid-1990s and the European Union bans the import of such tuna.
According to China's new industry standard, tuna sold as Sashimi must be processed in workshops where temperatures are below minus 10 degrees Celsius, rather than the current practice of spraying the CO gas to keep the fish looking fresh.
"The CO content in a kilogram of tuna must be lower than 200 milligrams," Professor Wu disclosed.
All CO-treated tuna will fail the standard, Huang said. 
He suggested an easier way for consumers to test whether tuna has been processed with CO or not.  "Though looking red and fresh, CO-treated tuna is tasteless and lacks its usual supple texture," he said.