The Murray cod (Maccullochella peelii) is a large Australian predatory freshwater fish. Although the species is called a cod in the vernacular, it is not related to the Northern Hemisphere marine cod (Gadus) species. The Murray cod is found in the Murray-Darling River system in Australia. The Murray cod is the largest exclusively freshwater fish in Australia, and one of the largest in the world. Other common names for Murray cod include cod, greenfish, goodoo, Mary River cod, Murray perch, ponde, pondi and Queensland freshwater cod.
The Murray cod is a large grouper-like fish with a deep, elongated body that is round in cross section. It has a broad, scooped head, and a large mouth lined with pads of very small, needle-like teeth. The jaws of this fish cod are equal, or the lower jaw protrudes slightly. Murray cod are white to cream on their ventral (belly) surfaces. Their backs and flanks are usually yellowish-green to green, overlain with heavy darker green, but occasionally brown or black, mottling. The effect is a marbled appearance sometimes reminiscent of a leopard’s markings. Coloration is related to water clarity; coloration is intense in fish from clear water habitats.
Murray cod are large fish, with adult fish regularly reaching 80–100 cm in length in all but the very smallest waterways. Murray cod are capable of growing well over one meter in length and the largest on record was over 1.8 m and about 113 kg in weight. Large breeding fish are rare in most wild populations today due to overfishing.
Murray cod are the most long-lived freshwater native fish in Australia. Longevity is a survival strategy in variable Australian environment to ensure that most adults participate in at least one exceptional spawning and recruitment event, which are often linked to unusually wet La Niña years and may only occur every one or two decades. The oldest Murray cod aged yet was 48 years of age, and the even larger specimens of years past leave little doubt that the species can reach considerably greater ages, of 70 years or more.
Fossils of fish anatomically identical to modern Murray cod have been unearthed in New South Wales from strata dating to 26 millions years ago. However, it is possible the species is as old as the Murray-Darling Basin itself about 50 to 60 million years. For more than 40,000 years, prior to European colonization aboriginal people were able to exploit the species as a major food source. They were impressed by the Murray cod, for in addition to being a major food source, it was the largest, most abundant and most beautiful of the native fish species. They had and still do have enormous respect and reverence for the Murray cod.
The importance of Murray cod to aboriginal people of the Murray-Darling basin is reflected by the fact that many groups living along the Murray River made the Murray cod a central animal in their mythology, including their creation stories. Many Murray River groups believed that the wide reaches and bends of the Murray River were created by a giant Murray cod, swimming down the formerly narrow trickle to the sea, while being pursued by a dream-time hero.
Explorers and early settlers were astounded by the abundance, size and delicacy of Murray cod with pioneers and early settlers relying on cod as a source of fresh food. From the 1860s, a large inland commercial fishery developed, based mainly on the Murray and Murrumbidgee rivers.There was a gradual decline from a peak in1918, and by the mid 1930s the fishery had become unprofitable for large operators. Between the mid 1950s and 1960s, there was a dramatic decline in the total commercial catch and the catch per fisherman. The catch remained at a low level until the New South Wales fishery closed in 2001. Today, most production comes from aquaculture systems with some finishing in earthen ponds, however limited production also comes from extensive ponds.
Murray cod have died out in many of their upland habitats, particularly in the southern Murray-Darling basin, due to a combination of overfishing from the late 1800s through 1950s, siltation, dams and weirs blocking migration, pollution from arsenic-based sheep-dips, mining, and in some cases, introduced trout stockings, which causes competition between juvenile Murray cod and introduced trout species. Invasive species, particularly the Redfin (Perca fluviatalis) and the Golden Carp, likely eat the young stages of Murray cod. Fingerlings produced by aquaculture are being released in hopes of increasing wild stocks.