A whale shark at Georgia Aquarium in Atlanta, Georgia, US, has died, the second at the facility to have perished this year.

Norton was one of the original whale sharks introduced at the aquarium in 2005, but was put down after his health rapidly declined.

Jeff Swanagan, president and executive director of the aquarium, said: “During the last few months, Norton stopped eating and started showing erratic swimming behaviour. In response, exhaustive diagnostic tests were conducted by husbandry and veterinary staff.

“Supplemental care was provided to Norton and our team was encouraged and hopeful his condition would improve.”

However, on Tuesday (12 June), husbandry staff noted a marked decline in the shark’s swimming behaviour, and subsequent blood tests confirmed his decline in health. Early on Wednesday, Norton stopped swimming and settled to the bottom.

The aquarium stated that “after every effort had been exhausted to improve Norton’s health, the team made the decision to humanely euthanise him.”

The aquarium, which is the only facility outside Asia to hold whale sharks in captivity, brought in two new whale sharks on 1 June.

Ralph, another of the aquarium’s original sharks, died in January of peritonitis, an inflammation of the membrane that lines the stomach cavity, but the cause of Norton’s death is as yet unknown. A autopsy will be carried out in the coming days.

The whale shark is the world’s largest fish and can reach lengths of more than 30ft (9m). It is found worldwide in tropical and subtropical waters. Despite its size, it is harmless to humans, feeding only on plankton and small fish.