BROWNSVILLE, Texas (ValleyCentral) — An investigation is underway after the Gladys Porter Zoo announced the death of five aquatic animals on Tuesday.

Aquarium staff at the zoo said the death of five stingrays at Stingray Landing in the Russell Aquatic Ecology Center as an “unexpected loss.”

According to a press release from Gladys Porter Zoo, all life support systems were fully operational, including the pump and filtration systems.

“At present, we are concentrating our efforts on determining the cause of this incident, and at this point are hoping that the diagnostic labs that will be looking at water and tissue samples will give us a clue as to what may have occurred,” said Patrick Burchfield, the zoo’s executive director.

Water and tissue samples will be sent to a veterinary diagnostic lab for further evaluation, the zoo said.

“The Gladys Porter Zoo is deeply committed to every animal in our care, and if there is something we need to do differently, we will do it,” the zoo said. “Using both internal and external expertise will help ensure that there are no unnecessary future losses.”

The deaths of the sting rays isn’t the zoo’s first. A group of stingrays died at the zoo last January due to an electrical issue.