DENVER (CBS4) – The staff at the Denver Zoo euthanized “Bertie,” a 58-year-old hippopotamus Monday morning.

Bertie, affectionately known as Bert, was the longest resident at the zoo.

Bert was also the oldest hippo in an accredited zoo in North America. Hippos live 30 to 40 years in the wild and up to about 50 years in the zoo.

“This is a very sad loss for Denver Zoo and our community. Bert was a member of our family for more than 50 years,” said Denver Zoo’s President/CEO Shannon Block in a news release. “He will be missed by all of us, including the many families and children who visited him and came to know his charismatic personality over the years.”

The decision to euthanize Bert came after significant decline in his quality of life. His caretakers had noticed he lost his appetite recently and was not interested in training sessions.

Bert was also reluctant to leave his pool and was having problems walking. The hippo had not responded well to medicines in the past, making it tough for veterinarians to treat him. When Bert’s caretakers decided he would not improve, they made the difficult decision to humanely euthanize him.

“This is never an easy decision, but it was the right one. We’ll all miss him very much, but were glad he lived such a long, happy life here at the zoo,” said Denver Zoo Vice President of Veterinary Medicine Scott Larsen in the same news release.

Bert came to Denver from New York’s Central Park Zoo on Dec. 16, 1958. He was the first hippo to ever reside at the zoo and he is the father of every hippo calf born at Denver Zoo.

While he fathered 29 hippopotamuses born at the zoo, he had only two mates.

The Denver Zoo is home to one other hippo, Bertie’s 12-year-old son, Mahali.