A Beluga whale, transferred with two others from the Georgia Aquarium to Sea World in San Antonio, Tex., died suddenly, the aquarium's veterinary officer said.

The cause of death of Nico, the 25-year-old male whale, on Monday is unknown and is pending the results of a necropsy, the Atlanta Journal-Constitution reported.

It is believed that Nico's death had nothing to do with the move, Dr. Gregory Bossart, the chief veterinarian, said.

"Usually when you have problems as the result of a transfer, it happens in first few days. And he's been there for nearly a month," Bossart said.

Nico had been rescued in October 2005 from substandard living conditions in a Mexico City amusement park. He suffered from liver problems, skin tumors and gastrointestinal issues, the newspaper reported.

"My take is the Georgia Aquarium rescued him and gave him a better quality of life," said Bossart, who, before joining the Atlanta aquarium, had examined Nico as a consultant in Mexico.

The aquarium has been vigilant about its beluga whales' health after two died there in 2007, the newspaper said.