New zealand blue cod
The New Zealand blue cod (Parapercis colias) is a temperate marine fish of the family Pinguipedidae. It is also known by its Māori names, rāwaru, pākirikiri and patutuki, and by its other names in English, Boston blue cod, New Zealand cod or sand perch.
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 Cook Strait. It is bluish green to blue-black above with white toward the belly. Large examples are usually greenish blue in colour, while smaller ones are blotched in varying shades of brown. An adult may grow to 60 cm in length and weigh from 1.0 to 3.0 kg. It feeds mainly on small fish and crabs. Blue cod is territorial. Spawning takes place in southern spring. Blue cod can also change sex from female to male.
It is an important recreational species in the South Island and is commercially harvested. Blue cod populations are managed under New Zealand's fisheries quota management system, although they are becoming scarce in some small areas due to fishing pressure. Annual catch range is between 2,000 and 2,500 tonnes.
Blue cod (P. colias) is not a cod. The use of blue cod can date back to the time of Captain Cook. Some early writers listed them as coal-fish which derived from unrelated European fish. However, this name is so widely used in New Zealand that it is unlikely to be changed.
Parapercis colias are protogynous hermaphrodites, which means they have both female and male reproductive organs at the beginning and some females change sex to males later in their life. P. colias is a marine bottom dwelling fish that is found in coastal New Zealand waters. Their colouring varies on age and sex. 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. As they mature with a body length over 25 cm, both sexes would have a blueish-grey dorsal with a white underside. Females have a tinge of orange and there is a trend for them to become green when they grow larger. Brownish pigments can be found at the base of pectoral fin. On the other hand, adult males have distinctive blue-grey colour coat with greenish sides and a golden brown line can be found above each eye. Body length of P. colias is about 30–40 cm in general, but can up to 60 cm and their weight is 0.8–1.5 kg in general, but can up to 3 kg. Males tend to be larger than females. They can live up to 32 years old.
Heads of P. colias are prominent and rounded with scales. They have a plump shaped body covered with firm scales. Above their non expanded cheeks are two large lateral eyes which can rotate independently, this allows them to see almost everywhere around them. P. colias possess a terminal mouth with bulbous lips. Their pelvic fins are generally placed forward on the throat with brown dots appear underneath it. There is a single horizontal stripe where ten to twelve scales above across their side of the body. The anterior section of their dorsal fin is small and short, followed by fins with five short spines. In contrast their second dorsal is long. A key used in an article of Cantwell can distinguish P. colias from other parapercids. Key features are listed below:
Other characters of detailed skeleton structures (osteology) of Parapercis species can be found in an article written by Gosline.
Swimming bladder is usually present in osteichthyids, it helps the fish to stay at a certain water pressure level (depth) without spending more energy. Swimming bladder in P. colias are absent. They will automatically sink to the sea floor if they stop swimming; therefore, they are called bottom-dwelling or sedentary bottom-hugging species. Their body shape of having a flattened abdomen indicates this as well. Normally, P. colias use their pectoral fin to swim, their body muscles and tails fin are only involved in swimming when a sudden burst or speed is needed, this type of swimming character is called labriform. As a result, their pelvic fins, used as props when they are resting on the seabed, are reduced and thicken. Due to their nature of being bottom-dwelling species, sand can clog their gills when they are resting. 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. Speaking of having a yawn, if you look closely you will notice that P. colias do not have palatine teeth and only have small teeth; however, you would not want to feel their sharp and well developed pharyngeal teeth near their throat like their prey.
There are some other detailed morphological characteristics inside the body of P. colias that determine their taxonomy, such as the presence of a lentiform body (an ocular vascular structure) and others, are mentioned by Eastman.
Pinguipedid fishes (Sandperches) are widely found in the southern Atlantic and Indo-Pacific regions. However, P. colias is endemic to New Zealand.
P. colias is found from the shore to the shelf edge around New Zealand's entire coastline, but there are no records in either the Kermadec Islands or the Snares Islands / Tini Heke. They are more abundant from south of Cook Strait and they are an iconic species for the South Island. They are most common around Southland and the Chatham Islands.
P. colias can be found at 150 m in depth occupying bedrock outcrops on gravel or sandy seabed. These habitats with macro algae or Sponges are even more preferred. Furthermore, their abundance in each habitat varies between age. 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 and deeper areas.
Since P. colias are generalists, which means that they prey on various species instead of depending on only one species, habitats that are rich in diversity of species are also favoured by them. An example of this is the kelp forest which is often established on rock beds where it is also desirable for P. colias. 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.
As mentioned before, P. colias can be found at 150 m in depth and was reported to be caught at 350m below the surface, other important aspects such as temperature, salinity and oxygen content in the ocean are often influenced by water depth. 766 samples were taken to determine the water temperature and chemistry ranges of P. colias as listed below:
Similar to other Parapercis species, male P. colias hold territories and their home range increases as the individual grows. Mutch found that they tend to hold large territories rather than but loose territories with small social groups that contain three to five females. Though they hold stable territories, P. colias moves from time to time. In a study, P. colias can move with on average of 2.09±2.12 km, this could potentially be home range shifts. It is reported 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.
Thunder is known to agitate the fish. Reports since the 1950s have documented thunder activating blue cod's flight mechanisms, causing the fish to leap out of aquariums.
P. colias seem to be migratory at certain times in a year, but little is known about their migration. Other studies indicated that they are relatively sedentary, however, long-term dispersal has been suggested due to a record that one individual travelled 156 km over 20 months.
Many fish species are generalists; thus, they are not limited by the predator-prey cycle. P. colias is one of them. They have been recorded to have 52 taxa in their diet, where adults are found to be more selective than juveniles. It makes sense that when P. colias grows bigger, the variety of species in their diet also increases, this includes polychaetes, crustaceans, molluscs, Pisces, algae and even its own spawn! This means that P. colias are omnivores which "feeds on more one trophic level". In short, you can say that they consume anything that is abundant and available locally. Other than the development of the fish itself, what they consume differs from region to region and whether the area is fished or not plays an important role as well. One study showed that oyster dredged habitat can reduce their prey diversity and have a negative effect on fish size. They usually stalk, seize and swallow their prey. After being caught, they tend to regurgitate the stomach contents.
‘Our Big Blue Backyard’ is a documentary of New Zealand marine and shoreline species. 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. They are also said to be voracious.
