It is a dark-spotted fish, with two dorsal fins. The first is short and low, and the second is a long anal fin, and a promindent sloping head, it varies in colour from a blue black to a greenish or grayish colour on it's sides and top, and white on the underside.

The Cod can grow to a maximum size of about 45cm, although the average size is around 28cm in length and weighs around 2.5kg

The Blue cod is a bottom dwelling fish generally likes cold water and inhabits rocky areas, and foul ground near the bottom upto a depth of about 150 metres. It is also very territorial and rarely moves long distances.

In saying this a recent government tagging experiment carried out in Foveaux Strait (Carbines, 2001) showed that although some blue cod moved as far as 156 km, 60.2% travelled less than 1 km.
http://services.fish.govt.nz/indicators/species.aspx?code=BCO

When I have been diving these fish have been seen perched on the bottom on their large pelvic and pectoral fins. They are very inquisitive and will approach you.

The Rock Cod is a carnivore and feeds mainly on small fish and crabs shellfish and other small crustaceans. It does this by stalking its prey and swallowing it whole.

The spawning season for this species is between late winter untill the early spring. It is beleived that these fish mate and spawn in deeper waters. The eggs are pelagic and for about five days, as are the larvae. After this stage the small juveniles then move from these deeper waters to the shallower areas closer inshore.
These juveniles are around 5cm and 10cm long. They are white in colour with 2 dark brown or black stripes on the back. When the fish grow to around 10cm these stripes fade to a light brown colour, befor turning to the blue grey adult colour