Premium Photo | A group of people dressed in Australian flagthemed attire Murray cod is the freshwater heavyweight of Australian rivers and lakes. It is an apex predator capable of growing to more than 1.8 metres long, and weighing in at more than 113kg. That?s a big fish and, as you would expect for a fish of this size, it ranks among the top ten biggest freshwater fish Cod Secrets: An Aussie Icon Par Rodney Mackenzie: Brand New Provincetown Secrets (A Cape Cod Series Book 6) - Kindle edition by... It is an apex predator capable of growing to more than 1.8 metres long, and weighing in at more than 113kg.