- Tuna are members of the Scombridae, or mackerel, family. Their common ancestors lived in warm tropical waters in the Miocene and Pliocene eras, more than 10 million years ago.

- Among the world's greatest travellers, the fastest-moving tuna, the bluefin, has been clocked at 70 miles (112 km) per hour and can accelerate to over 100 km per hour when chasing prey. They log thousands of miles in annual migrations between spawning and feeding grounds.

- Ocean-dwelling tuna live around the world, but usually spawn in tropical regions. Their circulatory systems regulate their body temperatures, so they can endure cold waters. Smaller types tend to stay in warmer waters, as the efficiency of body temperature regulation is proportionate to size.

- Small tropical skipjack, the world's most abundant tuna, usually weigh less than 5 kg (11 lb) and have a lifespan of less than five years. Like the bigger tropical-temperate yellowfin, albacore and bigeye tunas, their females spawn several million eggs, several times each year.

- Large, temperate, bluefin tuna often reach 500 kg, and adults are typically two metres long. They spawn after 10 years and can live up to 30 years.

- Overfishing is thought to have a worse impact on bluefin reproductive rates, because they take a decade to become sexually mature, and only spawn for a limited period in warm areas before migrating to cold feeding grounds.

- Approximately 2 million tonnes of tuna were caught worldwide in 2004, the UN Food and Agriculture Organisation says. Some 530,000 tonnes were supplied to Japanese markets in 2005, according to Japan's Fisheries Agency.

- In Oct. 2006 Japan agreed to nearly halve its southern bluefin catch to 3,000 tonnes a year for five years from 2007, after admitting to years of overfishing.

- Japan consumes more than half the world's most popular and expensive commercial tuna, the Atlantic bluefin. It is used in high-end sushi, and maguro and toro sashimi - thin slices of raw tuna and fatty tuna flesh.

- In Jan. 2001 Tokyo's famous Tsukiji Central Fish Market set a new record, selling a 201 kg bluefin for 20 million yen (US$165,000) or over US$800 per kg.

- The blue fin is also one of the most critically endangered commercial tuna species. Its spawning stock is down about 90 percent in the Indian Ocean because of overfishing, the WWF conservation group says.