Eastern Freshwater Cod - Age, Growth and Spawning

Age, Growth and Spawning

Growth is highly variable in eastern freshwater cod but overall is slower than in Murray cod. The oldest eastern freshwater cod yet aged is only 14 years of age, but this reflects limited sampling and many decades of overfishing and poaching, that have led to the loss of most large individuals (Butler & Rowland, 2008). There is little doubt the species has the potential to reach or even exceed the maximum age recorded in Murray cod (48 years).

Eastern freshwater cod are sexually mature at 4 or 5 years old, and at sizes as small as 700 g, the latter being markedly different to Murray cod (Butler & Rowland, 2008, 2009). This far smaller size at sexual maturity is likely an evolved adaptation to the rocky, low-nutrient and often quite small waterways eastern freshwater cod are found in. The trout cod, a Maccullochella cod also once found in small, rocky, low-nutrient streams in the upland reaches of the Murray-Darling system, displays a similar trait, also reaching sexual maturity at a far smaller size than Murray cod. Eastern freshwater cod spawn in early spring when water temperatures reach 16°C, using rock structures as sites for the adhesive eggs. Most other aspects of their spawning, including the guarding of eggs and newly hatched larvae by the male fish, are similar to Murray cod (Butler & Rowland, 2009). However, there are some indications that in contrast to Murray cod larvae, eastern freshwater cod larvae may not drift in river currents for several days after leaving their nest. This would be a notable difference in the larval ecology between the two species, however more research is required to confirm this.

It is important for anglers to avoid any accidental captures of eastern freshwater cod in winter when they are developing their roe, or in early spring when spawning is occurring, as research indicates this results in resorbed roe or abandoned nests respectively and a failed spawning effort (Butler & Rowland, 2009). There is now a total fishing closure on the Mann and Nymboida Rivers and their tributaries between 1 August to 31 October (inclusive) each year specifically to protect the eastern freshwater cod from accidental capture during their breeding season (NSW DPI, 2008).

It should be noted that anglers are not allowed to deliberately target eastern freshwater cod.