Blue cod

Parapercis colias is most commonly known as the blue cod (or more specifically the New Zealand blue cod or less commonly the Boston blue cod). It is also known in English as the New Zealand cod or the sand perch. In the indigenous Māori language, the species has a variety of names: , , , and . == Identification ==

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. On the other hand, adult males have distinctive blue-grey colour coat with greenish sides They have a plump shaped body covered with firm scales. P. colias possess a terminal mouth • The outer row of lower jaw has eight teeth • Dorsal spines longer to the posterior (rear end) • Soft dorsal fins have 20 rays and anal fins with 17 • 10 to 11 scales are present from lateral line to base of first soft dorsal ray • 23 to 26 counts of gill rakers • Caudal (tail) fins have 15 branched rays that looks rounded but bi-lobed. 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. 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. == Distribution ==

Natural global range Pinguipedid fishes (Sandperches) are widely found in the southern Atlantic and Indo-Pacific regions. However, P. colias is endemic to New Zealand. New Zealand range 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. They are more abundant south of Cook Strait and they are an iconic species for the South Island. They are most common around Southland and the Chatham Islands. == Habitat preferences ==

on a bedrock outcrop P. colias can be found at 150 m in depth or sandy seabed. These habitats with macro algae or Sponges are even more preferred. and deeper areas. 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. 766 samples were taken to determine the water temperature and chemistry ranges of P. colias as listed below: : ==Life cycle/phenology==

Spawning and hatching Multiple spawning events of a female P. colias occur throughout late winter and spring in the centre to the outer continental shelf. One male can be spawning with different groups of female. P. colias are protogynous hermaphrodites, when the length of P. colias reaches 410mm, 50% of the females are transitional. Sex inversion occurs with the colour change from whitish with a brown band at both sides or an orange tinge to bluish colour with a blue green band. Growth ring interpretation shows that they can live about 10 to 15 years, Maturity values are derived from the length of the fish. Besides, males generally have a faster growth rate compared to females. == Diet and foraging ==

Many fish species are generalists; thus, they are not limited by the predator-prey cycle. P. colias is one of them. It makes sense that when P. colias grows bigger, the variety of species in their diet also increases, this includes polychaetes, crustaceans, molluscs, algae and even its own spawn! and whether the area is fished or not plays an important role as well. 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. == Predators, parasites, and diseases ==

Predators Homo sapiens (humans) fish 2000 to 2500 tons of P. colias annually. Natural predators include: • Great white shark • Dolphins • Sea birds, such as mollymawks As many marine predators are generalists summarised the parasites found on blue cod including species in five main groups: Blood sucking sea lice are also known to parasitise P. colias. 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. An article suggests that small hooks cause more blood loss problems than big hooks to P. colias. this means that they do not suffer from barotrauma – an injury due expansion or eruption of the swimming bladder in fish, it is often caused by rapid water pressure change when rising from deep water to water surface. ==In a human context==

, Victoria (1907) Rāwaru was a valued traditional food for Māori who lived in the South Island, where the fish is more abundant. 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. The fish was an important species to early European settlers in New Zealand as a food source, and by the 1910s became even more popular in Australia, leading to the growth of the blue cod fishing industry in Southland. ==History of the name==

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. ==Economic and population management issue==

Blue cod is well known by the public due to its commercial and recreational importance. It is estimated that the marginal willingness to pay for an additional P. colias is $1.61 per fish and the average willingness to pay is $24.46 per fish. It is estimated that in 1999, 1.2 million P. colias was harvested, of which 70% were from the South Island. However, as the largest fish in the population would be the male, males are often being caught and is thought to affect the females changing their sex earlier. Surprisingly, the sex ratio male to females of P. colias is about 5:1 ==References==