A long-lived, slow-growing species, eastern freshwater cod are threatened by poaching [i.e. illegal take], habitat degradation, catastrophic natural events such as bushfires, and inbreeding from low genetic diversity.

Soft dorsal, anal, and caudal (tail) fins are all large and rounded, and are dusky grey or black with distinct white edges.

Their backs and flanks are usually an intense yellow or gold in colour, overlain with a dense pattern of black to very dark green mottling.

Subsequent isolation from Murray cod populations, the founder effect, genetic drift, and natural selection lead to allopatric speciation.

[5] The mechanism by which Murray cod crossed the Great Dividing Range are considered to be either river capture, where the headwaters of an easterly-flowing coastal river cuts back (in the erosional sense) and intercepts and "captures" the headwaters (and fish fauna) of a previously westerly flowing stream, or a "wet divide", where extreme flooding or a very wet climatic phase created swamps in a topographic low point that effectively connected the headwaters of western flowing and eastern flowing streams.

[5] DNA analysis reveals eastern freshwater cod of the Clarence River system went through one or more population bottlenecks before European settlement.

This was likely due to a sequence of catastrophic drought, whole-of-catchment-scale bushfire and severe, widespread ash-induced fish kills, similar to those which occurred in 1936 (see below).

Eastern freshwater cod numbers recovered from these pre-European bottleneck events, and the fish were abundant by the time of European settlement, but the species appears to have lost some genetic diversity.

The oldest specimen yet aged was only 14 years old, but this likely reflects limited sampling and many decades of overfishing and poaching that have led to the loss of most large individuals.

Eastern freshwater cod spawn in early spring when water temperatures exceed 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.

A total fishing closure is in effect on the Mann and Nymboida Rivers and their tributaries between August and October each year specifically to prevent this.

[1] Early records show that eastern freshwater cod were extremely abundant in the all parts of the Clarence River system at the time of European settlement.

[2][4][14] They were so abundant that they were caught "on demand" for diners at one riverside hotel,[15] and were reportedly even used as pig feed, as were the related Mary River Cod.

[19] This tin mining pollution caused many severe fish kills and was probably a key factor in the extirpation of eastern freshwater cod from large tracts of the Clarence River system in the 1930s.

While a high level of poaching is still taking place, legal protection has played a large role in finally allowing the species to commence a limited natural recovery.

[2][4][12] A restocking programme was undertaken by the government of New South Wales in 1984-1989, but was then closed and contracted to a private operation, which produced and stocked fingerlings until the late 1990s.

The fingerlings were contaminated with and introduced the banded grunter (Amniataba percoides), an aggressive small native fish, to the lower reaches of the river.