Murray cod (Maccullochella peelii) are the largest freshwater native fish in Australia. They were originally very common throughout the Murray-Darling basin. Mounted specimens and photos of long-ago giants are on display at almost every riverland pub in south-eastern Australia. After a few beers, old-timers come out with tall stories of fish bigger than a man, territorial lions of the river, big enough to drag unwary swimmers under by a paddling arm or kicking heel.
Murray cod are handsome fish, scales mottled with green and black roses and bellies silvery white. Their grouper-like bodies are deep and elongated, with broad, scooped heads and powerful blunt tails. They can weigh more than a hundred kilograms and measure over 1.6 metres. A long-lived fish, they’re known to reach at least seventy years of age. It’s likely they can live for much longer, a century or more. Murray cod are an ancient species and an animal central to Aboriginal mythology. Fossils have been found dating back twenty-six million years. They may well be as old as the Murray-Darling basin itself – sixty-five million years. That’s when the age of the dinosaurs was coming to an end.
Contrary to some fishery department literature, the first serious decline in Murray cod populations was caused by extreme overfishing by Europeans. In the latter half of the 1800s and in the1900s, they were caught in unimaginable numbers. In 1883, 150,000 kilograms of Murray cod were sent to Melbourne from Moama alone. This was a devastating blow to such a long-lived and slow-breeding species.
Cod mature at about four or five years old and breed in spring when water temperatures rise above fifteen degrees. They favour sheltered snags in the main channel of rivers. Males guard the eggs, and continue to watch over the newly hatched larvae for a week or more. The young fish then drift downstream.
Modern threats include exotic diseases, overfishing, pollution, dams and weirs blocking migration routes, and flood regulation for irrigation. Fifty percent of Murray cod larvae are killed when they pass through weirs, and cold water released from the base of dams stops adults spawning. Competition with introduced fish is also a problem, even though adult cod do a good job of eating carp.
It’s a great tragedy that these fabled fish are now extinct in many of their upland habitats, particularly in the southern Murray-Darling. They’re listed as critically endangered by the ICUN, a United Nations organization that maintains the Red List of Threatened Species. We can’t protect Murray cod without protecting the rivers that they live in. Let’s make it a priority!