Caspian, a 27-year-old beluga whale brought to Chicago from Marineland in Ontario, died Wednesday at Shedd Aquarium despite efforts to save her, the aquarium said Friday.

Veterinarians had watched her closely in recent weeks as she ate less than her full diet. Blood tests during the effort to save her showed abnormal electrolyte levels and blood pH, indicating a fluid imbalance and dangerously acidic blood. The aquarium said the results showed she was critically ill but did not establish why she died.

A necropsy is planned to look for underlying disease and a possible cause of death. Caspian is the fourth Marineland beluga to die at Shedd this year, after Peekachu, Rain and Osiris. Another beluga from the group, Jelly Bean, died at Oceanográfic Valencia in Spain. Shedd received 10 belugas from Marineland.