Two zoo minders try to measure a grouper fish. (Roland Magunia/AFP/Getty Images)
The groper was found on Townsville's Strand beach on Wednesday morning.
An autopsy examination by veterinary pathologist Ian Anderson found the groper had a turtle in its stomach.
Queensland Minister for Primary Industries Tim Mulherin said gropers were top predators and would eat anything they could fit in their mouths, including small sharks and stingrays.
"It was a mature fish, 218cm long, about 25 years old and weighed in at about 150kg," Mr Mulherin said.
"The shell of the turtle was measured at 40cm."
Dr Anderson is part of a taskforce investigating the deaths of a number of gropers that had occurred along the east coast in the past two years.
He said when he arrived the fish was lying on its side in shallow water and was in obvious distress.
"It died a short time later and we have taken a number of samples for further analysis," he said.
"I do not believe the groper's final meal of a juvenile green turtle actually killed the fish and there were no external injuries."
Gropers are a protected species in Queensland.
The state's biggest recorded specimen was more than three metres long and weighed 288kg.
To report a sick or injured groper call Queensland Primary Industries and Fisheries on 13 25 23.
