The Vancouver Aquarium says a virus or toxin likely killed its sole beluga whale, just a week after her daughter suffered the same fate.

In a press conference to discuss Friday's sudden death of 29-year-old Aurora, the facility said the marine mammal had liver damage, but results of its necropsy are inconclusive and there were "no obvious signs of mortality."

Dr. Martin Haulena, the facility's head veterinarian, said the whale's liver was "dramatically compromised" although that didn't show up in any blood work.

"Our most likely culprits for this are either a virus or toxin given the course of disease, given the lack of significant findings both in clinical diagnostics and early post mortem results," said Haulena.

Haulena said he will not rest until he finds some answers on what killed the beloved whales.

The longtime vet said both cetaceans had the same clinical symptoms and laboratory results, and the battle to save them was "hard fought."

"We have to assume their deaths are related," he said.

"We're still seeking clarity on why the two whales displayed similar symptoms during the very sudden onset of their illnesses and the test results we've received to date are inconclusive," said Aquarium CEO John Nightingale, adding the health and wellbeing of its animals are of paramount concern.

Veterinarians had been keeping a close eye on their last beluga following the "sudden loss" of Aurora's daughter, 21-year-old Qila, on Nov. 16.

The day after Qila died, Aurora seemed to be suffering from similar symptoms, but then started to show signs of recovery. Then again, the aquarium said it was "increasingly concerned" for her health, but Friday said she had started playing and seeking rubs from her trainers, behaviour she hadn't exhibited since Qila's death.

But despite consulting with veterinary specialists, pathologists, marine biologists and "other experts from around-the-world" to provide treatment and investigate her ailment, her life could not be saved.

"The passing of two animals in a situation like this, never mind two whales, in a two week period is unprecedented in our 60-year history," Nightingale said.

The aquarium currently has five other belugas on loan to other facilities. But Nightingale said there will be no more marine mammals at the facility until they find out what killed Aurora and Qila.

The planned expansion of its beluga tanks are still in the planning and design phase, but no construction will take place, said Nightingale.

Part of the investigation into the whale deaths will include a "full 360" review of the aquarium operations, looking at everything from water quality to dietary changes.

An expert panel of pathologists and forensic medical experts from the veterinary and medical fields will be established to do a deep dive into what happened.

They are not ruling out the possibility that the whales were deliberately poisoned.

"We're waiting for more test results in hopes they will provide an explanation," said Nightingale. "Absolutely nothing is off the table."

The past two weeks have been incredibly trying for the hundreds of aquarium staff and volunteers, said Nightingale, adding that there has been an outpouring of support for the team trying to save the marine mammals.

"This is the very reason we have those whales is to engage people and begin the process of raising awareness," said Nightingale.

The deaths have reignited the debate over whether whales should be kept in captivity.

The California-based In Defense of Animals hopes the tragedy will encourage the aquarium to stop taking in whales.

The group encourages the public to sign a petition directed at the Vancouver Park Board and Vancouver Aquarium CEO, asking the aquarium to end all whale and dolphin captivity and move remaining cetaceans to "retirement facilities."

Nightingale said he's sick of the "hot air and misinformation" spread by those who are against having whales in captivity.

"If any one of those activists does 1/1700th as one of our employees or volunteers then we can talk," he said.

Aurora's history at the aquarium

Aurora was taken from the Western Hudson Bay beluga population, the last acquired by the aquarium before it instituted its policy of only accepting cetaceans born in captivity. She was named after the aurora borealis, and "immediately won hearts and inspired generations of visitors, employees and volunteers with her curious nature and gentle personality," the aquarium said.

The aquarium wrote that her 26 years at the facility allowed staff to teach millions of visitors about her species and belugas' ecosystem in the wild.

She'd also helped with studies into whales' physiology, hearing and communication between mothers and calves. Aurora's daughter, Qila, was the first beluga ever conceived and born in a Canadian aquarium. The whales were both part of studies dating back to 2002.

Aurora had other babies during her time at the aquarium, but her offspring did not survive. One of the babies lived three years, and the other died after only one year. Her daughter Qila also gave birth, but the young whale died at the age of three.

The aquarium was well known for its resident belugas, one of which inspired the Raffi song "Baby Beluga." That whale, Kavna, died at the age of 46 in 2012.