Two newly imported, rare Chinese sturgeons have died at Ocean Park from a viral infection, the park said yesterday.
The two fish had been in quarantine since they were imported from the mainland on February 18, along with 13 other Chinese sturgeons, or Acipenser sinensi, that had been bred in captivity, a park spokeswoman said.
They were found swimming "abnormally" on April 21 and May 11 and given "immediate support" by the park's animal care and veterinary teams, but they died shortly after.
An examination of the first Chinese sturgeon - which is of a species dating back 140 million years - indicated a gill infection, while the second was believed to have died of an infection of several internal organs.
The source of the viral infection has yet to be determined.
The spokeswoman added that the park would monitor the remaining 13 sturgeons, and liaise with the Yangtze River Fisheries Research Institute to confirm the source of the infection.
Staff from the institute have also agreed to visit the park to examine the remaining sturgeons this week.
The National Aquatic Wildlife Conservation Association and other research institutes on the mainland were also advising on the problem, she said.
Nine Chinese sturgeons are on display in the park's Chinese Sturgeon Aquarium.
Some of the imported newcomers will eventually replace six existing sturgeons at the park, which will be returned to the mainland when they reach the required size for tagging, before being released to the wild.
An investigation will be conducted at the park and a report will be sent to the relevant local and mainland departments.
From 2008 to 2009, three Chinese sturgeons imported from the mainland died at the park.
The first was killed by a barracuda, while experts said two others died because of their reaction to salination.
Wild Chinese sturgeons are classified as an endangered species and are among the nation's most protected species.
There are more than 1,000 Chinese sturgeons that have been bred in captivity on the mainland.