Ocean Park has lost its second sturgeon, this time from an infection that staff are still trying to identify. Two of the remaining eight sturgeon had shown similar symptoms and were moved out of their aquarium. They were now out of danger, a park spokeswoman said. The fish died on Wednesday after symptoms of an infection that did not respond to treatment, she said. It was 10 years old, about 2 metres long and was bred in captivity. 'Right now, I really can't tell what caused the death and the infection. We are still investigating and waiting for results from the laboratory,' the spokeswoman said. The six sturgeon still in the aquarium will be moved while it is closed for checking and cleaning, she said. Ocean Park lost a sturgeon in June when one died from a bite by a barracuda kept in the same tank, triggering criticism the park was wrong to house the species together. After mainland experts inspected the facilities, Beijing decided to send five more sturgeons, considered 'national treasures', taking the total to nine. Park chairman Allan Zeman pledged at the time they would do their best to ensure their safety. Chinese sturgeon, which have changed little in 140 million years, are rarer than pandas, with fewer than 1,000 in existence. Mr Zeman expressed sadness over the death and said the park would work with mainland experts to review care. He had confidence in the skills and dedication of his staff. Two other sturgeon had shown similar symptoms and were taken out of the aquarium for observation and medical attention. 'They are OK now and are observed to be stable,' the spokeswoman said. A spokeswoman for the Tourism Commission said it had asked Ocean Park to consider whether measures might be needed. 'We have been assured by Ocean Park that experts from the park and the mainland are working closely together to investigate the cause of the death and to step up remedial measures for the other sturgeon,' she said. The park said it had not delayed the release of the news. 'We told the Hong Kong government as well as the relevant mainland authorities immediately,' she said. The park said it was in contact with the mainland's National Aquatic Wildlife Conservation Association, the Yangtze River Fisheries Research Institute of the Chinese Academy of Fisheries Sciences, and the Beijing Aquarium. Experts will come to Hong Kong by the end of the month to consult. Wei Qiwei, researcher at the Yangtze River Fisheries Research Institute, where the second batch of five sturgeon came from, said, 'Now it is still very unclear', adding that he would come here next week.