Robert De Niro's restaurant chain Nobu sells endangered tuna

At three Nobu restaurants in London, investigators from the environmental group Greenpeace ordered tuna dishes described on the menu only by Japanese terms for the cut of the fish they were from.

They asked staff to identify the tuna species used. Samples were later tested to determine the type. Dishes from all three were Atlantic bluefin.

The distinction is important because the Atlantic bluefin and the southern bluefin are listed as critically endangered by the International Union for the Conservation of Nature's Red List because of overfishing. Most sushi eaten in Britain is from less endangered species such as yellowfin, but Japanese chefs are known to consider bluefin the most delicious.

Nobu does not specify on its menus which species of tuna it serves. Requests for the information by campaigners have been met for several years with a terse "no comment".

Although it is not illegal to serve Atlantic bluefin, also known as northern bluefin, many chefs, including Gordon Ramsay, have dropped it because of concern that fishing is at higher levels than stocks can withstand. At Nobu Berkeley St, which has one Michelin star, investigators asked for Atlantic bluefin (hon maguro in Japanese) but staff told them the restaurant did not stock it.

Dr Sergi Tudela, of WWF Mediterranean, said: "It is scandalous for a restaurant chain as globally famous as Nobu not to be clear about what it sells - and misleading to the discerning consumer who is trying to do the right thing.

"The accurate traceability of seafood products is essential to avoid the overexploitation of fragile species."

Willie Mackenzie of Greenpeace said: "Nobu and Robert De Niro are clearly making a great deal of money serving up endangered fish and they were reported this year as trying to sell a controlling share of their restaurant chain at a valuation of $400 million.