[5] It is exclusively found in New Zealand, in shallow waters around rocky coasts to a depth of 150 m, though it is far more common south of the Cook Strait.

[7] Large examples are usually greenish blue in colour, while smaller ones are blotched in varying shades of brown.

[16] Juveniles start off being generally pale in colour and have two long dark stripes along the sides which will turn brown and barely distinguishable when they become middle-sized fish.

[7] On the other hand, adult males have distinctive blue-grey colour coat with greenish sides[21] and a golden brown line can be found above each eye.

[25] Key features are listed below:[25] Other characters of detailed skeleton structures (osteology) of Parapercis species can be found in an article written by Gosline.

[27] Swimming bladder is usually present in osteichthyids,[28] it helps the fish to stay at a certain water pressure level (depth) without spending more energy.

[29] They will automatically sink to the sea floor if they stop swimming; therefore, they are called bottom-dwelling or sedentary bottom-hugging species.

[31] To remedy this, P. colias often hold their breath and open their mouths for a long interval like having a yawn to take good gulps of air every now and then.

[11][16] Juvenile are found more frequently in sponge gardens (more than 16m deep) dominated by orange finger sponges (Raspalia topsenti & Raspalia flaccida), large black massive sponge (Ancorina alata) and the small bright yellow clumps of Polymastia granulosa that provide more shelters and safer refuges, whereas adults are mainly found on reef margins[30] and deeper areas.

[39][40][37] However, they can be also found in less species diverse habitats such as barren rock flats (4-12m deep) that are dominated by sea urchins grazing on algae.

It has been regarded as a sign of potential sex change by reducing egg production for saving the resource.

[41] Their growth rate can differ due to food supply, water temperature and habitat as other fish do.

[18] Similar to other Parapercis species, male P. colias hold territories and their home range increases as the individual grows.

[45] It is reported[34] that P. colias emigrate from coastal to offshore waters in May of each year, this is thought to be a preparation for mating and spawning in early winter.

Reports since the 1950s have documented thunder activating blue cod's flight mechanisms, causing the fish to leap out of aquariums.

Other studies indicated that they are relatively sedentary,[49][50][45] however, long-term dispersal has been suggested due to a record that one individual travelled 156 km over 20 months.

[53] It makes sense that when P. colias grows bigger, the variety of species in their diet also increases, this includes polychaetes, crustaceans, molluscs,[12][37][9][53][34] Pisces,[37][54] algae and even its own spawn!

[55][9] One study[9] showed that oyster dredged habitat can reduce their prey diversity and have a negative effect on fish size.

[57] In the Chatham Islands episode, blue cod (P. colias) waits to feed on pāua, an endemic sea-snail that attaches itself on hard surfaces such as rocks, at its most vulnerable phases – when they move or are grasped up by a starfish using hundreds of tube feet.

[54] Hewitt and Hine[62] summarised the parasites found on blue cod including species in five main groups: Blood sucking sea lice are also known to parasitise P.

[63] Despite having greater risk for parasitic, bacterial, or fungal infections, mortality after having a hook injury is often caused by blood loss rather than disease.

[65] Rāwaru was a valued traditional food for Māori who lived in the South Island, where the fish is more abundant.

[48] Heads of rāwaru (P. colias, blue cod) were often given back to the sea as offerings to the god Maru before Māori return from fishing.

[18] The value of P. colias as being the third popular recreational fishing species cannot be ignored,[17] this includes using their flesh as rock lobster bait.

[17] To achieve sustainable fishing, it is crucial to persist healthy population structure with continuous monitoring and quotas set to date.

In addition, the fundamental unit of concern of its management of population is the genetic structure that can lead to the reduction of the evolutionary potential for responding to environmental change, the increase of inbreeding risk and the force of selective genetic change.

[46] Since a number of evidence indicated that blue cod are relatively sedentary,[49][50][45][46] the fishing pressure may lead to potential local depletion.

[70][46] On the other hand, the differences within mainlandList of islands of New Zealand populations were limited while the pattern of the isolation by distance was detected.