After a three-week chase through icebergs in the Antarctic, Australian and South African officials seized a Uruguayan fishing boat they say was loaded with 85 tons of rare and illegally-caught Patagonian toothfish. Now, they find themselves embroiled in a diplomatic dispute with Uruguay.

In the dead of night, in sub-Antarctic waters, Australian and South African officers boarded the Uruguayan-flagged fishing boat, the Viarsa, believed to be loaded with an estimated $2 million worth of the endangered fish.

For three weeks, Australian customs and fisheries officers, backed by armed South African enforcement officers, had chased the Viarsa across 6,400 kilometers of ferocious seas between Africa and South America. The Australians charge that the ship had been fishing illegally in Australian waters.

The Viarsa, with 40 crew on board, repeatedly ignored orders to stop for a search, and often dodged through dangerous icebergs to shake off its pursuers.

Finally, the ship was surrounded, and armed officials climbed aboard and arrested the crew.

Australia's minister for fisheries, Ian MacDonald, says a huge catch of Patagonian toothfish, better known as Chilean sea bass, was discovered on board the Viarsa.

"So far, we have the captain's log, which indicates that the vessel is carrying about 85 tons of fish, suspected of being toothfish," he said.

To the surprise of the Australian and South African pursuers, a Uruguayan government observer was also found on board. The Uruguayan government has demanded that the official, and the ship, be turned over to Uruguay.

Mr. MacDonald says the request will be considered, but he says the ship is headed for the west coast of Australia, after being refueled in South Africa, and the trip to Australia could take a month.

Under Australian law, the ship and the catch can be confiscated by the government. The crew members, mostly from Uruguay, Chile and Spain, could face a year in jail and fines of at least $350,000, if they are convicted of poaching.

Mr. MacDonald says Australia is determined to stamp out poaching of the fish.

"This operation will send a very clear message to illegal operators that the Australian government will go to the ends of the earth, literally, to apprehend those suspected of fishing illegally," said Australia's minister for fisheries.

The highly-valued fish, also known as "white gold," is a favorite in restaurants in the United States and Japan, but poaching has pushed the species close to extinction.