The only white dolphin in captivity has died in central China.

It is believed that Qi Qi - which was a member of the world's most endangered species of dolphin - died of old age.

The dolphin, which was 24 or 25 years old, had a life span that was "the equivalent of a 70-year-old man" according to an official at the Hydrobiology Institute of the Chinese Academy of Sciences.

He did quite well to live so long

Hydrobiology Institute official

The death could complicate efforts by China to save one of the world's rarest animals.

Qi Qi was caught in 1980 by a fisherman in the Yangtze River, the main habitat for the species which is unique to China.

Chinese scientists had hoped to use the animal in an artificial breeding programme to boost the species' chances of survival. The dolphin is one of just four freshwater dolphin species.

It is estimated there are fewer than 100 of white dolphins remaining in the Yangtze River.

Deadly pollution

Scientists fear the dolphins may become extinct in two decades, after having populated the river for 25 million years.

River traffic, pollution and development are said to be the main problems facing the dolphins.

The exact cause of Qi Qi's death will be investigated at the Hydrobiology Institute in Wuhan, Hubei Province, where he spent more than 22 years, mostly swimming alone in a 300-square-metre (3,230-square-feet) pool.

An official told the Associated Press news agency that the dolphin had suffered from diabetes and stomach problems as he approached the end of his natural life span.

"Qi Qi was the equivalent of a 70-year-old man. He did quite well to live so long," she said.