Blue cod

{{Short description|Species of ray-finned fish}} {{About|the New Zealand reef fish|the North Pacific deep-sea fish (Anoplopoma fimbria) called blue cod in the United Kingdom|Sablefish}} {{Use New Zealand English|date=July 2016}} {{Speciesbox | image = Parapercis colias (Blue cod).jpg | status = LC | status_system = IUCN3.1 | status_ref = <ref name = IUCN>{{cite iucn |author=Collen, B. |author2=Richman, N. |author3=Beresford, A. |author4=Chenery, A. |author5=Ram, M. (Sampled Red List Index Coordinating Team) |year=2010 |errata=2017 |title=''Parapercis colias'' |article-number=e.T154870A115246940 |doi=10.2305/IUCN.UK.2010-4.RLTS.T154870A4655851.en}}</ref> | taxon = Parapercis colias | authority = (Forster, 1801) | synonyms = *''Percis nicthemera'' Cuvier in Cuvier & Valenciennes, 1829 *''Enchelyopus colias'' Forster in Bloch & Schneider, 1801 | synonyms_ref = <ref name = FishBase>{{FishBase|Parapercis|colias|month=February|year=2018}}</ref> }}

The '''New Zealand blue cod''' ('''''Parapercis colias''''') is a temperate marine ray-finned fish<ref name="Carbines2004.a" /> of the family Pinguipedidae.<ref name="NZOR">{{cite web| url=http://www.nzor.org.nz/names/7c8168dd-6bff-4c73-8d42-ff7c29015a4b |title=Blue cod |website=New Zealand Organisms Register| date=2018| access-date=2018-04-15}}</ref> It is also known as '''Boston blue cod''', '''New Zealand cod''', and '''sand perch''', and by its Māori names, {{lang|mi|rāwaru}}, {{lang|mi|pākirikiri}}, and {{lang|mi|patutuki}}.<ref name="MPIname">{{cite web| url=http://www.mpi.govt.nz/dmsdocument/964-specification-of-scientific-names-of-fish | title=New Zealand List of Scientific Names of Fish |publisher=Ministry for Primary Industries | date=2018| access-date=2018-04-15}}</ref>

It is exclusively found in New Zealand, in shallow waters around rocky coasts to a depth of {{cvt|150|m|-1}}, though it is far more common south of Cook Strait.<ref name="Carbine1998" /> It is bluish green to blue-black above with white toward the belly.<ref name="Paulin1989" /> Large examples are usually greenish blue in colour, while smaller ones are blotched in varying shades of brown.<ref name="Paulin1989" /> An adult may grow to {{cvt|60|cm}} in length and weigh from {{cvt|1.0|to|3.0|kg}}.<ref name="Hirt-Chabbert" /><ref name="JiangCarbine" /> It feeds mainly on small fish and crabs.<ref name="Russell">{{cite journal|last1=Russell| first1=B. C. |year=1983| title=The food and feeding habits of rocky reef fish of north-eastern New Zealand| journal=New Zealand Journal of Marine and Freshwater Research|volume=17 |issue=2|pages=121–145| doi=10.1080/00288330.1983.9515991| bibcode=1983NZJMF..17..121R }}</ref> Blue cod is territorial.<ref name="Mutch" /> Spawning takes place in southern spring.<ref name="AylingCox" /><ref name="PankhurstConroy" /> Blue cod can also change sex from female to male.<ref name="Carbines1998'" />

It is an important recreational species in the South Island and is commercially harvested.<ref name="Paul.a" /><ref name="Paul.b" /> 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.<ref name="MPI2018" /> Annual catch range is between 2,000 and 2,500 tonnes.<ref name="MPI2014" />

== Names == ''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: {{lang|mi|kopukopu}},<ref>{{Māori Dictionary|42268|Kopukopu}}</ref> {{lang|mi|pākirikiri}},<ref>{{Māori Dictionary|5030|Pākirikiri}}</ref> {{lang|mi|pātutuki}},<ref>{{Māori Dictionary|43777|Pātutuki}}</ref> {{lang|mi|rāwaru}}<ref>{{Māori Dictionary|6652|Rāwaru}}</ref> and {{lang|mi|taipua}}.<ref>{{Māori Dictionary|15294|Taipua}}</ref>

''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.<ref name="Carbines.b" /> ''P. colias'' is a marine bottom dwelling fish that is found in coastal New Zealand waters.<ref name=MPI2018/> Their colouring varies on age and sex.<ref name="Paul.b" /> 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.<ref name="MPI2018" /><ref name="Paul.a" /><ref name="EoL" /> As they mature with a body length over 25 cm, both sexes would have a blueish-grey dorsal with a white underside.<ref name="MPI2018" /> Females have a tinge of orange and there is a trend for them to become green when they grow larger.<ref name="Paul.b" /> Brownish pigments can be found at the base of pectoral fin.<ref name="Paulin1989">{{cite book| last1=Paulin| first1=C.D. | year=1989| title= New Zealand fish, a complete guide |publisher=Te Papa Press }}</ref> On the other hand, adult males have distinctive blue-grey colour coat with greenish sides<ref name="Paulin1998" /> and a golden brown line can be found above each eye.<ref name="Paul.b" /> 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.<ref name="Hirt-Chabbert" /><ref name="JiangCarbine" /> Males tend to be larger than females. They can live up to 32 years old.<ref name=MPI2018/>

Heads of ''P. colias'' are prominent and rounded with scales.<ref name="AylingCox" /><ref name="Hirt-Chabbert" /><ref name="McDowall" /><ref name="Paul1993">{{cite book | last1=Paul| first1=L.J. | last2=Moreland| first2=J.M. | last3=Heath | first3=E.W. | year=1993| title=Handbook of New Zealand marine fishes | publisher=Reed}}</ref> They have a plump shaped body covered with firm scales.<ref name="Paul.b" /> Above their non expanded cheeks are two large lateral eyes<ref name="McDowall" /> which can rotate independently, this allows them to see almost everywhere around them.<ref name="RH">{{cite book|last1=Whalley-Torckler |first1=G |last2=Torckler |first2=D |year=2003 |title= Life-size guide to New Zealand fish |publisher=Random House New Zealand}}</ref> ''P. colias'' possess a terminal mouth<ref name="Paulin1989" /> with bulbous lips.<ref name="AylingCox" /><ref name="RH"/> Their pelvic fins are generally placed forward on the throat with brown dots appear underneath it.<ref name="Paulin1998" /> There is a single horizontal stripe where ten to twelve scales above across their side of the body.<ref name="Paulin1989" /> The anterior section of their dorsal fin is small and short,<ref name="Paul.a" /><ref name="Paulin1998" /> followed by fins with five short spines.<ref name="Hirt-Chabbert" /> In contrast their second dorsal is long.<ref name="Paulin1998" /> A key used in an article of Cantwell can distinguish ''P. colias'' from other parapercids.<ref name="Cantwell" /> Key features are listed below:<ref name="Cantwell">{{cite journal | last=Cantwell | first=G. E. | year=1964 | title=A revision of the genus ''Parapercis'', family Mugiloididae | journal=Pacific Science | volume=18 | issue=3 | pages=239–80| url=https://scholarspace.manoa.hawaii.edu/bitstream/10125/5533/1/vol18n3-239-280.pdf}}</ref>

*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.<ref>{{cite book|last1=Gosline |first1=W.A. |year=1968 |title=The suborders of perciform fishes |publisher=The United States National Museum| url=https://repository.si.edu/bitstream/handle/10088/17019/1/USNMP-124_3647_1968.pdf}}</ref>

Other characters of detailed skeleton structures (osteology) of ''Parapercis'' species can be found in an article written by Gosline.<ref>{{cite journal|last1=Gosline |first1=W. A. |year=1963 |title=Notes on the osteology and systematic position of ''Hypoptychus dybowskii'' Steindachner and other elongate perciform fishes |url=https://scholarspace.manoa.hawaii.edu/bitstream/10125/4929/1/vol17n1-90-101.pdf|journal=Pacific Science|volume=17|number=1}}</ref>

Swimming bladder is usually present in osteichthyids,<ref>{{cite book|last1=Kotpal|first1=R. L. |year=2010|title= Modern text book of zoology: vertebrates |publisher= Rastogi Publications }}</ref> it helps the fish to stay at a certain water pressure level (depth) without spending more energy. Swimming bladder in ''P. colias'' are absent.<ref name="Blackwell" /> They will automatically sink to the sea floor if they stop swimming; therefore, they are called bottom-dwelling or sedentary bottom-hugging species.<ref name="Thompson" /> Their body shape of having a flattened abdomen indicates this as well.<ref name="Thompson" /> 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.<ref name="Thompson" /> As a result, their pelvic fins, used as props when they are resting on the seabed,<ref name="AylingCox" /> are reduced and thickened.<ref name="Thompson" /> Due to their nature of being bottom-dwelling species, sand can clog their gills when they are resting.<ref name="Graham1997">{{cite book|last1=Graham|first1=J.B. |year=1997|title= Air-breathing fishes: evolution, diversity, and adaptation | publisher=Academic Press}}</ref> 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.<ref name=Graham1997 /> Speaking of having a yawn, if you look closely you will notice that ''P. colias'' do not have palatine teeth<ref name="Paulin1989" /> 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.<ref name="Thompson" />

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.<ref name="Eastman">{{cite journal| last1=Eastman |first1=J.T. | year=2006 | title= Aspects of the morphology of phyletically basal bovichtid fishes of the Antarctic suborder Notothenioidei (Perciformes) |journal= Polar Biology |volume=29 | issue=9 | pages=754–763 | doi=10.1007/s00300-006-0112-y|bibcode=2006PoBio..29..754E |s2cid=7523756 | hdl=1834/17098 | hdl-access=free }}</ref>

== Distribution ==

=== Natural global range === Pinguipedid fishes (Sandperches) are widely found in the southern Atlantic and Indo-Pacific regions.<ref name="Nelson">{{cite book| last1=Nelson | first1=J.S. | year=1994 | title=Fishes of the World |publisher=John Wiley & Sons, Inc.}}</ref> However, ''P. colias'' is endemic to New Zealand.<ref name="Stroud">{{cite thesis| last1=Stroud | first1=G.J. | year=1982 | title=The taxonomy and biology of fishes of the genus Parapercis (Teleostei: Mugiloididae) in Great Barrier Reef waters |publisher=James Cook University|degree=PhD}}</ref><ref name="Martin&Hine">{{cite book| last1=Martin | first1=E | last2=Hine | first2=R. | year=1996 | title=A Dictionary of Biology |publisher=Oxford University Press | edition=3}}</ref>

=== 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.<ref name="Francis">{{cite journal | last1=Francis | first1=M.P. | year=1996 | title=Geographic distribution of marine reef fishes in the New Zealand region | journal=New Zealand Journal of Marine and Freshwater Research |volume=30 |issue= 1 |pages=35–55 |doi=10.1080/00288330.1996.9516695| doi-access=free | bibcode=1996NZJMF..30...35F }}</ref> They are more abundant south of Cook Strait<ref name="Paul.b">{{cite book| last1=Paul | first1=L.J. | year=2000 | title=New Zealand fishes: identification, natural history & fisheries |publisher=Reed}}</ref> and they are an iconic species for the South Island.<ref name=MPI2018>{{cite web |url= https://www.mpi.govt.nz/travel-and-recreation/fishing/fish-species/blue-cod/ |title=blue cod |author= Ministry for Primary Industries |date=2018 |access-date=2018-04-15}}</ref> They are most common around Southland and the Chatham Islands.<ref name="Carbine1998">{{cite web |url=http://fs.fish.govt.nz/Doc/22465/BC09702%20Blue%20Cod%20in%20Southland.pdf.ashx |title=Determination of movement of blue cod in Southland |author= Carbines, G. |date=1998 |access-date=2018-04-15}}</ref>

== Habitat preferences == [[File:Blue Cod in Milford Sound.jpg|thumb|Blue cod in Milford Sound on a bedrock outcrop]]

''P. colias'' can be found at 150 m in depth<ref name="Carbine1998" /><ref name="Hirt-Chabbert">{{cite book| last1=Hirt-Chabbert| first1=J. | year=2006| title=Fish species of New Zealand: a photographic guide |publisher=Reed books}}</ref><ref name="Paul.b" /> occupying bedrock outcrops on gravel<ref name="AylingCox">{{cite book| last1=Ayling| first1=T. | last2=Cox |first2=G.J. | year=1982| title=Collins guide to the sea fishes of New Zealand |publisher=Collins}}</ref><ref name="Graham" /><ref name="Paul.a">{{cite book| last1=Paul| first1=L.J. | year=1997| title=Marine Fishes of New Zealand 1: Shoreline and Shallow Seas. |volume=1 |publisher=Reed}}</ref><ref name="Paulin1998">{{cite book| last1=Paulin| first1=C.D. | year=1998| title=Common New Zealand marine fishes |publisher=Reed}}</ref> or sandy seabed.<ref name="BeentjesCarbines">{{cite journal | last1=Beentjes | first1=M. | last2=Carbines | first2=G. | year=2005| title=Population structure and relative abundance of blue cod (''Parapercis colias'') off Banks Peninsula and in Dusky Sound, New Zealand | journal=New Zealand Journal of Marine and Freshwater Research |volume=39 | issue=1 |pages=77–79 |doi=10.1080/00288330.2005.9517293| bibcode=2005NZJMF..39...77B | s2cid=86285680 }}</ref> These habitats with macro algae or Sponges are even more preferred.<ref name="BeentjesCarbines" /> Furthermore, their abundance in each habitat varies between age.<ref name="Mutch">{{cite thesis| last1=Mutch | first1=P.G. | year=1983 | title=Factors influencing the density and distribution of the P. colias, Parapercis colias. Pisces: Mugiloidae|degree=MSc}}</ref><ref name="Paul.b" /> 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<ref name="Thompson">{{cite book| last1=Thompson| first1=S.M. | year=1981 | title=Fish of the marine reserve. A guide to the identification and biology of common coastal fish of northeastern New Zealand |publisher=University of Auckland| url=http://www.thebookshelf.auckland.ac.nz/docs/Fish%20of%20the%20marine%20reserve/1%20frontmatterandintroduction.pdf}}</ref> and deeper areas.<ref name="Paul.b" />

Since ''P. colias'' are generalists,<ref name="JiangCarbine">{{cite journal | last1=Jiang| first1=W. | last2=Carbines | first2=G. | year=2002| title=Diet of blue cod, ''Parapercis colias'', living on undisturbed biogenic reefs and on seabed modified by oyster dredging in Foveaux Strait, New Zealand. | journal=Aquatic Conservation: Marine and Freshwater Ecosystems |volume=12 |issue=3 |pages=257–272 |doi=10.1002/aqc.495| bibcode=2002ACMFE..12..257J }}</ref> 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''.<ref name="coleaylingcreese">{{cite journal | last1=Cole| first1=R.G. | last2=Ayling| first2=T.M. |last3=Creese |first3=R.G. | year=1990| title=Effects of marine reserve protection at Goat Island, northern New Zealand. | journal=New Zealand Journal of Marine and Freshwater Research |volume=24 |issue=2 |pages=197–210 |doi=10.1080/00288330.1990.9516415| doi-access=free | bibcode=1990NZJMF..24..197C | hdl=2292/4936 | hdl-access=free }}</ref><ref name="FosterS">{{cite book| last1=Foster| first1=M.S. |last2=Schiel |first2=D.R. | year=1985 | title=Ecology of giant kelp forests in California: a community profile |publisher=Moss Landing Marine Labs.}}</ref><ref name="Graham">{{cite book| last1=Graham| first1=D.H. | year=1956 | title=A treasury of New Zealand fishes. |publisher=Reed.}}</ref> 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.<ref name="Thompson" />

As mentioned before, ''P. colias'' can be found at 150 m in depth and was reported to be caught at 350m below the surface,<ref name="Carbine1998" /> other important aspects such as temperature, salinity and oxygen content in the ocean are often influenced by water depth.<ref name="McDowall">{{cite journal | last1=McDowall | first1=R.M. | year=1973| title=Relationships and taxonomy of the New Zealand torrent fish, ''Cheimarrichthys fosteri'' Haast (Pisces: Mugiloididae). | journal=Journal of the Royal Society of New Zealand |volume=3 |issue=2 |pages=199–217 |doi=10.1080/03036758.1973.10430602| doi-access=free | bibcode=1973JRSNZ...3..199M }}</ref> 766 samples were taken to determine the water temperature and chemistry ranges of ''P. colias''<ref name="EoL" >{{cite web |url= http://eol.org/ |title= ''Parapercis colias'' Blue Cod. |author=Encyclopedia of Life. |date= 2018 |access-date=2018-04-15 }}</ref> as listed below: :{||- ! scope="col" width="width: 1000em;" | ! scope="col" width="width: 20em;" | ! scope="col" width="width: 20em;" | |- |Temperature: | 7.786 - 18.158 | (°C) |- |Nitrate: | 0.205 - 18.689 | (μmol/L) |- |Salinity: | 34.283 - 35.544 | (PPS){{clarify|date=November 2024}} |- |Oxygen: | 5.121 - 6.587 | (mL/L) |- |Phosphate: | 0.258 - 1.333 | (μmol/L) |- |Silicate: | 1.911 - 7.690 | (μmol/L) |- |}

==Life cycle/phenology==

===Spawning and hatching=== Multiple spawning events of a female ''P. colias'' occur throughout late winter and spring<ref name="AylingCox" /><ref name="PankhurstConroy">{{cite journal | last1=Pankhurst| first1=N.W. | last2=Conroy| first2=A.M.| year=1987| title=Seasonal changes in reproductive condition and plasma levels of sex steroids in the blue cod, ''Parapercis colias'' (Bloch and Schneider) (Mugiloididae). | journal=Fish Physiology and Biochemistry |volume=4 |issue=1 |pages=11–26 |doi=10.1007/BF02073862| pmid=24226034 | bibcode=1987FPBio...4...15P | s2cid=34714507 }}</ref> in the centre to the outer continental shelf.<ref name="Paul.b" /> Instead of a distinct spawning episode, their spawning is a continuous event that the eggs are released over time.<ref name="BrandtDunnBrouwer">{{cite journal | last1=Brandt| first1=K.K. | last2=Dunn| first2=M.R.| last3=Brouwer | first3=S.L. | year=2017| title=Assessing maturity, fecundity and hermaphroditism in blue cod ''Parapercis colias''. | journal=Aquatic Biology |volume=26 |pages=137–148 |doi=10.3354/ab00679 | doi-access=free | bibcode=2017AquaB..26..137B }}</ref> One male can be spawning with different groups of female.<ref name="Hirt-Chabbert" /> Eggs could possibly drift 74 km away from the spawning site and hatch potentially after 116 hours.<ref name="Robertson1980" /> Young fish are found below 20 metres<ref name="Paulin1998" /> then move to shallow water in summer.<ref name="Paul.b" />

===Age, growth, sex and maturity=== Growth of ''P. colias'' is measured by the relationship between age and their body length.<ref name="BeentjesCarbines2012">{{cite journal | last1=Beentjes | first1=M.P. | last2=Carbines | first2=G.D. | year=2012| title=Relative abundance, size and age structure, and stock status of blue cod from the 2010 survey in Marlborough Sounds, and review of historical surveys. | journal=New Zealand Fisheries Assessment Report |volume=43 |issue=137}}</ref> ''P. colias'' are protogynous hermaphrodites,<ref name="Carbines1998'" >{{cite book| last1=Carbines |first1=G.D. |year=1998 |title=Blue cod age validation, tagging feasibility and sex-inversion. Final Research |publisher=Unpublished report, Ministry for Primary Industries}}</ref> when the length of ''P. colias'' reaches 410mm, 50% of the females are transitional.<ref name="Carbines.b">{{cite thesis |last1=Carbines |first1=G.D. |year=2004 |title=Age, growth, movement and reproductive biology of blue cod (''Parapercis colias'' – Pinguipedidae): Implications for fisheries management in the South Island of New Zealand |degree=Ph.D. |publisher=University of Otago |page=225 |hdl=10523/8082 |url=http://hdl.handle.net/10523/8082}}</ref> 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.<ref name="AylingCox" /> Though sex inversion found to occur across a wide range of age and size, the cause of activating the sex inversion has not been well understood.<ref name="BeentjesCarbines" /> Studies have shown that the proportion of sex change decreases afterwards<ref name="Carbines.b" /> as the presence of males in the population would discourage sex change.<ref name="BeentjesCarbines" /> Hence, it is regarded as a response to the demographic structure in the population instead of a response to their size.<ref name="BeentjesCarbines" /> Another study indicated that blue cod is most fecund at the size which closes to the average size of the first maturity of males. It has been regarded as a sign of potential sex change by reducing egg production for saving the resource.<ref name="BrandtDunnBrouwer" /> Sex change is also not well described that the transitional gonads has different definitions.<ref name="BrandtDunnBrouwer" />

Their growth rate can differ due to food supply, water temperature and habitat as other fish do.<ref name="Paul.b" /> Sex can also influence the growth rate. Male grow faster and larger than female.<ref name="Carbines2004.a" >{{cite journal | last1=Carbines |first1=G.D. | year=2004 | title=Age determination, validation, and growth of blue cod ''Parapercis colias'', in Foveaux Strait, New Zealand | journal=New Zealand Journal of Marine and Freshwater Research | volume=38 |issue=2 |pages=201–214|doi=10.1080/00288330.2004.9517231|s2cid=84616975 |doi-access=free |bibcode=2004NZJMF..38..201C }}</ref><ref name="Paul.b" /> ''P. colias'' have the potential to grow up to 50 cm in length and weight 4 kg.<ref name="Ayling1987" >{{cite book| last1=Ayling |first1=T. |last2=Cox |first2=G.J. |year=1987 |title=Collins guide to the sea fishes of New Zealand (Revised edition).| publisher=William Collins Publishers Ltd.|page=343}}</ref> Growth ring interpretation shows that they can live about 10 to 15 years,<ref name="Paul.b" /> but a study showed that the known maximum age of blue cod is 23 years old.<ref name="RodgersWing">{{cite journal | last1=Rodgers | first1=K.L. | last2=Wing | first2=S.R. | year=2008| title=Spatial structure movement of blue cod ''Parapercis colias'' in Doubtful Sound, New Zealand, inferred from δ13C and δ15N | journal=Marine Ecology Progress Series |volume=359 |pages=239–248 |doi=10.3354/meps07349| bibcode=2008MEPS..359..239R | doi-access=free }}</ref>

Maturity values are derived from the length of the fish.<ref name="BeentjesCarbines2012" /> Their growth rate varies between locations.<ref name="Mutch" /><ref name="Smith" /> For example, male can reach maturity when their length reached 10–19 cm (which is about 2–3 years old) in Northland, but in Southland the male needs to reach 26–28 cm (which is about 4–6 years old).<ref name="Smith">{{cite book | last1=Smith | first1=H.M. | year=2012 | title=Characterisation of the mitochondrial genome and the phylogeographic structure of blue cod (''Parapercis colias'').| url=http://researcharchive.vuw.ac.nz/xmlui/bitstream/handle/10063/2139/thesis.pdf?sequence=2}}</ref> Besides, males generally have a faster growth rate compared to females.<ref name="Carbines2004.a" /><ref name="Mutch" /><ref name="Paul.b" /> Both female and male ''P. colias'' are assumed to reach sexual maturity with the measuring of 28 cm.<ref name="Carbines.b" /> The maximum lifespan of ''P. colias'' is 32 years.<ref name="MPI2014" />

===Behaviours=== Similar to other ''Parapercis'' species, male ''P. colias'' hold territories and their home range increases as the individual grows.<ref name="Mutch" /> Mutch found that they tend to hold large territories rather than but loose territories with small social groups that contain three to five females.<ref name="Govier" /> Though they hold stable territories, ''P. colias'' moves from time to time. In a study,<ref name="Carbine1998" /> ''P. colias'' can move with on average of 2.09±2.12 km, this could potentially be home range shifts.<ref name="RodgersWing" /> It is reported<ref name="Stroud" /> 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.<ref name="Secrets"/>

===Migration=== ''P. colias'' seem to be migratory at certain times in a year,<ref name="Paul.b" /> but little is known about their migration. Other studies indicated that they are relatively sedentary,<ref name="ColeVilloutaDavidson">{{cite journal | last1=Cole |first1=R.G. | last2=Villouta | first2=E. | last3=Davidson | first3=R.J. | year=2000 | title=Direct evidence of limited dispersal of the reef fish ''Parapercis colias'' (Pinguipedidae) within a marine reserve and adjacent fished areas. | journal=Aquatic Conservation: Marine and Freshwater Ecosystems | volume=10 |issue=6 |pages=421–436 | doi=10.1002/1099-0755(200011/12)10:6<421::AID-AQC423>3.0.CO;2-E}}</ref><ref name="MaceJohnston">{{cite journal | last1=Mace |first1=J.T. | last2=Johnston | first2=A.D. | year=1983 | title=Tagging experiments on blue cod (Parapercis colias) in the Marlborough Sounds, New Zealand. | journal=New Zealand Journal of Marine and Freshwater Research | volume=17 |issue=3 |pages=207–211 | doi=10.1080/00288330.1983.9515998| doi-access=free |bibcode=1983NZJMF..17..207M }}</ref><ref name="RodgersWing" /> however, long-term dispersal has been suggested due to a record that one individual travelled 156 km over 20 months.<ref name="CarbinesMcKenzie">{{cite book | last1=Carbines | first1=G.D. | last2=McKenzie | first2=J. | year=2004 | title=Movement patterns and stock mixing of blue cod in Dusky Sound in 2002.| publisher=New Zealand Fisheries Assessment Report 2004/36}}</ref>

== Diet and foraging == Many fish species are generalists; thus, they are not limited by the predator-prey cycle.<ref name="Murdoch">{{cite journal| last1=Murdoch| first1=P.J.| last2=Oaten| first2=A.| year=1975| title=Predation and population stability.| journal=Advances in Ecological Research| volume=9| pages=[https://archive.org/details/advancesinecolog0000unse/page/1 1–131]| doi=10.1016/S0065-2504(08)60288-3| bibcode=1975AdER....9....1M| isbn=978-0-12-013909-5| url-access=registration| url=https://archive.org/details/advancesinecolog0000unse/page/1}}</ref> ''P. colias'' is one of them.<ref name="JiangCarbine" /><ref name="Paulin1998" /><ref name="Paul.b" /> They have been recorded to have 52 taxa in their diet,<ref name="JiangCarbine" /> where adults are found to be more selective than juveniles.<ref name="Jones">{{cite journal | last1=Jones| first1=G.P. | year=1988| title=Ecology of rocky reef fish of north-eastern New Zealand: a review. | journal=New Zealand Journal of Marine and Freshwater Research |volume=22 |issue=3 |pages=445–642 |doi=10.1080/00288330.1988.9516315| doi-access=free | hdl=2292/4942 | hdl-access=free }}</ref> It makes sense that when ''P. colias'' grows bigger, the variety of species in their diet also increases, this includes polychaetes, crustaceans, molluscs,<ref name="AylingCox" /><ref name="Graham" /><ref name="JiangCarbine" /><ref name="Jones" /><ref name="Stroud" /> Pisces,<ref name="Graham" /><ref name="Young">{{cite journal | last1=Young| first1=M.W. | year=1929| title=Marine fauna of the Chatham Islands. | journal=Transactions and Proceedings of the New Zealand Institute |volume=60 |pages=136–166}}</ref> algae and even its own spawn!<ref name="Young" /> This means that ''P. colias'' are omnivores which "feeds on more one trophic level".<ref name="PimmLawton">{{cite journal | last1=Pimm| first1=S.L. | last2=Lawton| first2=J.H. | year=1978| title=On feeding on more than one trophic level. | journal=Nature |volume=275 |issue=5680 |page=542| doi=10.1038/275542a0| bibcode=1978Natur.275..542P | s2cid=4161183 }}</ref><ref name="Stroud" /> In short, you can say that they consume anything that is abundant and available locally.<ref name="Paul.b" /><ref name="Paul1993"/> Other than the development of the fish itself, what they consume differs from region to region<ref name="JiangCarbine" /><ref name="Sylvester">{{cite book | last1=Sylvester | first1=T. | year=1986| title=Food limitation: a preliminary study on two groups of benthic feeding carnivorous fish in a temperate reef system.|page=87}}</ref> and whether the area is fished or not plays an important role as well.<ref name="PimmLawton" /><ref name="JiangCarbine" /> One study<ref name="JiangCarbine" /> 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.<ref name="Paul.b" /> After being caught, they tend to regurgitate the stomach contents.<ref name="Graham" />

"Our Big Blue Backyard" is a documentary of New Zealand marine and shoreline species.<ref name="NHNZ">{{cite web |url=https://www.tvnz.co.nz/shows/our-big-blue-backyard/episodes/s2-e3 |title=Our Big Blue Backyard – Season 2, Episode 3 |author=Natural History New Zealand |date=2016 |publisher=Natural History New Zealand, Ltd |access-date=2018-04-15}}</ref> 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.<ref name="NHNZ" /> They are also said to be voracious.<ref name="NHNZ" /><ref name="Stroud" />

== Predators, parasites, and diseases == === Predators === ''Homo sapiens'' (humans) fish 2000 to 2500 tons of ''P. colias'' annually.<ref name="MPI2014" >{{cite web |url= http://fs.fish.govt.nz/Doc/23548/08_BCO%202014%20FINAL.pdf.ashx |title=Fisheries Assessment Plenary May 2014: Stock Assessments and Stock Status. Blue Cod (BCO)|author= Ministry for Primary Industries |date=2014 |access-date=2018-04-15}}</ref> Natural predators include: *Great white shark<ref name="NHNZ" /> *Benthic feeders, such as: **Yellow-eyed penguins<ref name="Chilvers2014">{{cite journal | last1=Chilvers| first1=B.L. | last2=Dobbins| first2=M.L. | last3=Edmonds| first3=H.K.| year=2014| title= Diving behaviour of yellow-eyed penguins, Port Pegasus/Pikihatiti, Stewart Island/Rakiura, New Zealand. | journal=New Zealand Journal of Zoology |volume=41 |issue=3 |pages=161–170| doi=10.1080/03014223.2014.908931 | s2cid=87018205 }}</ref><ref name="Moore">{{cite journal | last1=Moore| first1=P.J. | last2=Wakelin| first2=M.D. | year=1997| title=Diet of the yellow-eyed penguin ''Megadyptes antipodes'', South Island, New Zealand, 1991-1993. | journal=Marine Ornithology |volume=25 |pages=17–29| doi=10.5038/2074-1235.25.1.377 }}</ref><ref name="Van">{{cite journal|last1=Van Heezik|first1=Y.|author-link=Yolanda van Heezik|year=1990|title=Diets of yellow-eyed, Fiordland crested, and little blue penguins breeding sympatrically on Codfish Island, New Zealand.|journal=New Zealand Journal of Zoology|volume=17|issue=4|pages=543–548|doi=10.1080/03014223.1990.10422952|doi-access=free}}</ref> **Dolphins<ref name="Federal">{{cite journal | last1=Federal Register| year=2015| title=Endangered and Threatened Wildlife and Plants; Notice of 12-Month Finding on a Petition To List Bottlenose Dolphins in Fiordland, New Zealand as Threatened or Endangered Under the Endangered Species Act. | journal=Federal Government of United States |url=https://www.federalregister.gov/documents/2015/06/19/2015-15087/endangered-and-threatened-wildlife-and-plants-notice-of-12-month-finding-on-a-petition-to-list}}</ref> *Sea birds, such as mollymawks<ref name="Govier">{{cite thesis |last1=Govier |first1=D. |year=2001 |title=Growth and movement of Blue Cod (Parapercis colias) in Paterson Inlet, Stewart Island, New Zealand |degree=M.Sc |publisher=University of Otago |hdl=10523/2967 |url=http://hdl.handle.net/10523/2967}}</ref>

As many marine predators are generalists<ref name="Murdoch" /> there are many other potential predators not listed. ''P. colias'' are known to predate upon juveniles of their own species.<ref name="Young" />

=== Parasites === Hewitt and Hine<ref name="HewittHine">{{cite journal | last1=Hewitt| first1=G.C. | last2=Hine| first2=P.M. | year=1972| title= Checklist of parasites of New Zealand fishes and of their hosts. | journal=New Zealand Journal of Marine and Freshwater Research |volume=6 |issue=1–2 |pages=69–114| doi=10.1080/00288330.1977.9515410| doi-access=free | bibcode=1972NZJMF...6...69H }}</ref> summarised the parasites found on blue cod including species in five main groups:

{| class="wikitable" style="text-align: left;" |- ! style="width:20em;" |Group ! style="width:20em;" |Species ! style="width:20em;" |Location on host |- |Protozoa | *''Trypanosoma parapercis'' | *Blood |- |Digenea | *''Pancreadium otagoensis'' *''Plagioporus(Caudotestis) pachysomus'' *''Steringotrema rotundum'' *''Lecitocladium excisum'' *''Gonocerca phyddis'' | *Intestine *Intestine *Gall bladder and stomach *Stomach *Stomach |- |Monogenea | *''Microcotyle constricta'' | *Gills |- |Nematoda | *''Anisakis'' sp. larva *Contracaecum ''(Thynnascaris)'' sp. larva | *Viscera, mesenteries and under peritoneum *Stomach, intestine and body cavity |- |Copepoda | *''Aethon percis'' *''Caligus buechlerae'' | *Gills *Skin |}

Blood sucking sea lice are also known to parasitise ''P. colias''.<ref name="NHNZ" />

=== Disease and injuries === No specific disease is found on ''P. colias'', but some injuries have been recorded. Hooking injuries could cause tissue damage and possibly lead to mortality.<ref name="Carbines1999" >{{cite journal | last1=Carbines |first1=G. | year=1999 | title=Large hooks reduce catch-and-release mortality of blue cod ''Parapercis colias'' in the Marlborough Sounds of New Zealand | journal=North American Journal of Fisheries Management | volume=19 |issue=4 |pages=992–998|doi=10.1577/1548-8675(1999)019<0992:LHRCAR>2.0.CO;2|bibcode=1999NAJFM..19..992C }}</ref> 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.<ref name="Meka" >{{cite journal |last1=Meka |first1=J.M. |year=2004| title=The Influence of Hook Type, Angler Experience, and Fish Size on Injury Rates and the Duration of Capture in an Alaskan Catch-and-Release Rainbow Trout Fishery |journal=North American Journal of Fisheries Management | volume=24 |issue=4 |pages=1309–1321 |doi=10.1577/M03-108.1|bibcode=2004NAJFM..24.1309M }}</ref> An article suggests that small hooks cause more blood loss problems than big hooks to ''P. colias''.<ref name="Carbines1999" />

Compared to other bony fish, swimming bladder in ''P. colias'' is absent,<ref name="Blackwell" >{{cite web |last1=Blackwell |first1=R.G. |year=2014 |title=Abundance, size and age composition, and yield-per-recruit of blue cod in the Marlborough Sounds, September 1996| publisher=NIWA |url=http://fs.fish.govt.nz/Doc/22460/BCO2003-01%20Blue%20Cod%20Marlborough%20Sounds%20Tasman%20Bay%20abundance%20size%20Objective%201%202%203%20final.pdf.ashx}}</ref> 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.<ref name="Thorncraft">{{cite journal| last1=Thorncraft |first1=G. |last2=Baumgartner |first2=L.J. |last3=Boys |first3=C.A. |last4=Brown |first4=R.S. |year=2013 | title=Merging hydraulics with biology |journal=International Water Power & Dam Construction | volume=65 |issue=1 |pages=42–43}}</ref>

==In a human context== [[File:An exhibit of cod by one of the colony's big customers (1907) (cropped).jpg|thumb|A display of smoked blue cod in Melbourne, Victoria (1907)]]

Rāwaru was a valued traditional food for Māori who lived in the South Island, where the fish is more abundant.<ref name="Secrets">{{citeq|Q114871191|pp=148-153}}</ref> 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.<ref name="Best" >{{cite journal| last1=Best | first1=E. |year=1929 |title=Fishing methods and devices of the Maori | journal=Dominion Museum Bulletin}}</ref>

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.<ref name="Secrets"/>

==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.<ref name="Paul.b" /><ref name="Paul1993" /> 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.<ref name="Paul.b" />

==Economic and population management issue== [[File:New Zealand blue cod dish, Corner House, Singapore Botanic Gardens - 20170126.jpg|thumb|A dish of blue cod and Hokkaido scallops in a restaurant in Singapore]]

Blue cod is well known by the public due to its commercial and recreational importance.<ref name="Paul.a" /><ref name="Paul.b" /> As mentioned before, we fish 2000 to 2500 tones of ''P. colias'' per year.<ref name="MPI2014" /> The value of ''P. colias'' as being the third popular recreational fishing species cannot be ignored,<ref name="MPI2018" /> this includes using their flesh as rock lobster bait.<ref name="Robertson1980" >{{cite journal| last1=Robertson |first1=D.A.| year=1980 |title=Hydrology and the quantitative distribution of planktonic eggs of some marine fishes of the Otago Coast, South-eastern New Zealand |journal=Fisheries Research Bulletin | volume=21 |url=http://docs.niwa.co.nz/library/public/frb21.pdf}}</ref> 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.<ref name="Williamson2000">{{cite conference| last1=Williamson| first1=S.| year=2000 | title=The Economic Value of New Zealand Marine Recreational Fishing and its Use as a Policy Tool |conference=International Institute of Fisheries Economics & Trade (IIFET) 2000, "Microbehavior and Macroresults" |location=Corvallis, Oregon, USA |book-title=IIFET 2000 Proceedings| url=https://ir.library.oregonstate.edu/downloads/fx719n336}}</ref> It is estimated that in 1999, 1.2 million ''P. colias'' was harvested, of which 70% were from the South Island.<ref name="Williamson2000" /> Thus, Ministry for Primary Industries (New Zealand) has set minimum capture length and maximum capture limit of ''P. colias'', which varies between areas mainly depending on abundance, to avoid depletion. For example, in the South-East area (of South Island from Clarence Point to Southland and extended to the Chatham Islands, New Zealand), no fish shorter than 30 cm can be taken and each fisher has a limit up to 30 fish per day.<ref name="MPI2018" />

To achieve sustainable fishing, it is crucial to persist healthy population structure with continuous monitoring and quotas set to date.<ref name="MPIs" >{{cite book| author=Ministry for Primary Industries |year=2016| title=New Zealand's Sustainable Fisheries| url=http://www.mpi.govt.nz/dmsdocument/11096-new-zealands-sustainable-fisheries}}</ref> 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.<ref name="BeentjesCarbines" /> This is an emerging issue to all hermaphrodites.<ref name="Robinson" >{{cite journal| last1=Robinson |first1=O. J.|last2=Jensen|first2=O. P |last3=Provost | first3=M. M.|last4=Huang | first4=S.| last5=Fefferman| first5=N. H.| last6=Kebir| first6=A.| last7=Kebir| first7=A.| last8=Lockwood| first8=Julie | year=2016| title=Evaluating the impacts of fishing on sex-changing fish: a game-theoretic approach| journal=ICES Journal of Marine Science| volume=74| issue=3| pages=652–659| doi=10.1093/icesjms/fsw222| doi-access=free}}</ref> Surprisingly, the sex ratio male to females of ''P. colias'' is about 5:1<ref name="Carbines.b" /> which is biologically implausible. This suggests that sex changes might not purely depend on fish length, but we cannot ignore the fact that fishery has changed the natural population composition of "P. colias". To understand the direct impact on P. colias despite population decline<ref name="BeentjesCarbines" /> further research is required.

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.<ref name="Smith" /> Since a number of evidence indicated that blue cod are relatively sedentary,<ref name="ColeVilloutaDavidson" /><ref name="MaceJohnston" /><ref name="RodgersWing" /><ref name="Smith" /> the fishing pressure may lead to potential local depletion.<ref name="CarbinesMcKenzie" /> Recent studies showed that the genetic differences were significant between mainland List of islands of New Zealand population and Chatham Island population.<ref name="Gebbie" /><ref name="Smith" /> 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.<ref name="Smith" /> Further research using microsatellite DNA markers suggested that some significant genetic differences between mainland population exist which indicate the potential long-distance dispersal, but the dispersal rate is too low to have demographic effect in the population.<ref name="Gebbie">{{cite thesis| last1=Gebbie| first1=C. L.| year=2014| title=Population genetic structure of New Zealand blue cod (''Parapercis colias'') based on mitochondrial and microsatellite DNA markers |degree=MSc |publisher=Victoria University of Wellington| url=http://researcharchive.vuw.ac.nz/handle/10063/4245}}</ref>

==References== {{Reflist}} * {{ITIS |id=170968 |taxon=Parapercis colias |access-date=30 January 2006}} * {{FishBase |Parapercis|colias |year=2005|month=October}}

==External links== * {{cite web|url=http://www.fish.govt.nz/en-nz/Recreational/Most%2BPopular%2BSpecies/Blue%2BCod/Default.htm|url-status=dead|archive-url=https://web.archive.org/web/20070212043039/http://www.fish.govt.nz/en-nz/Recreational/Most%2BPopular%2BSpecies/Blue%2BCod/Default.htm|archive-date=12 February 2007|title=Blue Cod Fishing and a link to the Blue Cod Fishing Regulations|publisher= Ministry of Fisheries}} {{Fish of New Zealand}} {{Taxonbar|from=Q2492416}}

Category:Parapercis Category:Endemic marine fish of New Zealand cod, blue Category:Fish described in 1801 Category:Taxa named by Johann Reinhold Forster