Murray & Trout Cod Differences
Anglers who fish in waters where trout cod occur need to be able to differentiate the species from Murray cod. This is because trout cod are an endangered species and are totally protected by law. The water where you are most likely to encounter trout cod is in the Murray River from Yarrawonga downstream to the Barmah Forest. Trout cod are also sometimes encountered in other areas, for example in Seven Creeks near Euroa downstream of the closed section (of course there are trout cod in the closed section but being closed to angling, we are not allowed to fish there) and in other areas as a result of the trout cod re-stocking program. Hopefully as time passes these other populations will increase; of course this will mean that more anglers will accidentally encounter them.
How to identify trout cod
The key differences for an angler between these two closely related species are in the following areas (this is not intended to be a scientific description):
Eye stripe
Trout cod usually have a black or at least dark horizontal stripe on the side of the head, level with the pupil of the eye, although sometimes the stripe is missing, broken or indistinct. Juvenile Murray cod can also have this stripe but only in small fish well under legal size, which must be released anyway.
If you see an eye stripe, let it go.
Head and body markings, colouration
Murray cod generally have an overall olive green colouration, often with a vivid white belly. The markings are of a mottled appearance, although they appear more spotted in very large individuals. The same general colouration and patterning continues right across the body and head.
Trout cod generally have a more blue-grey colouration with a grey belly which often looks "dirty", especially under the chin. The dark markings have a more speckled appearance and usually reduce in number and size over the head, and are sometimes almost completely absent there. The base colour of the fish often intensifies over the head, giving rise to the alternate name "blue nose cod".
Do not rely on body colour alone to identify a fish as a Murray cod, many trout cod have a distinctly greenish colour.
If the head looks different to the body in colouration or markings, let it go.
Lower Jaw
The lower jaw is shorter than the upper in trout cod, but this can be hard to see in a fish on the end of the line in the water.
In Murray cod the lower jaw is either the same length or slightly longer than the upper.
If it has a short lower jaw, let it go.
Head shape
Murray cod generally have a concave head profile with a relatively blunt, broad snout, whereas trout cod have a straight or slightly convex profile with a more pointed, narrower snout. The head profile can be confused by the shoulder of the fish which in larger specimens can make a straight head look concave to the casual observer.
If it has a pointy snout, let it go.
Other points
There is no difference in the shape, colouration, or position of the fins. Overall body shape, except as noted above is also the same.
Trout cod are generally more aggressive than Murray cod and often out fight them. Some anglers have described trout cod as being like "Murray cod on steroids".
NSW DPI documents