Editing Murray cod

{{Short description|The largest Australian predatory freshwater fish in the family Percichthyidae}}
{{About-distinguish|the Australian freshwater fish|Cod}}
{{Good article}}
{{Use Australian English|date=June 2020}}
{{Use dmy dates|date=August 2019}}
{{Speciesbox
| status = VU
| status_system = EPBC
| status_ref = <ref name=sprat>{{Cite web|url=https://www.environment.gov.au/cgi-bin/sprat/public/publicspecies.pl?taxon_id=66633 |title= ''Maccullochella peelii'' — Murray Cod|date=3 July 2003|website=[[Species Profile and Threats Database]]|access-date=23 August 2023| archive-url=https://web.archive.org/web/20230823051045/https://www.environment.gov.au/cgi-bin/sprat/public/publicspecies.pl?taxon_id=66633| archive-date=23 August 2023| url-status=live}}</ref>
| status2 = LC
| status2_system = IUCN3.1
| status2_ref = <ref name="iucn status 19 November 2021">{{cite iucn |author=Gilligan, D. |author2=Zampatti, B. |author3=Lintermans, M. |author4=Koehn, J. |author5=Butler, G. |author6=Brooks, S. |date=2019 |title=''Maccullochella peelii'' |volume=2019 |page=e.T12576A103325360 |doi=10.2305/IUCN.UK.2019-3.RLTS.T12576A103325360.en |access-date=19 November 2021}}</ref>
| image = Murray cod02 melb aquarium.jpg
| image_caption = At [[Sea Life Melbourne Aquarium]], [[Melbourne]]
| genus = Maccullochella
| species = peelii
| authority = ([[Thomas Livingston Mitchell|T. L. Mitchell]], 1838)
| synonyms = * ''Acerina peelii'' <small>T. L. Mitchell, 1838</small>
* ''Maccullochella peelii peelii'' <small>(T. L. Mitchell, 1838)</small>
}}

The '''Murray cod''' ('''''Maccullochella peelii''''') is a large Australian predatory freshwater [[fish]] of the genus ''[[Maccullochella]]'' in the family [[Percichthyidae]].<ref name="FOA">Dianne J. Bray & Vanessa J. Thompson (2011) [http://fishesofaustralia.net.au/home/species/4655#classification Murray Cod, Maccullochella peelii]. Fishes of Australia. Retrieved 29 August 2014</ref> Although the species is called a [[cod]] in the [[vernacular]], it is not related to the Northern Hemisphere marine cod (''[[Gadus]]'') species. The Murray cod is an important <!-- 'hyperbole' and charismatic -->part of Australia's [[vertebrate]] wildlife—[[#Diet|as an apex predator]] in the [[Murray-Darling]] River system—and also [[#Relationship with humans|significant in Australia's human culture]].<ref name=":1">{{cite book |last1=Humphries |first1=Paul |title=The Life and Times of the Murray cod |date=2023 |publisher=CSIRO Publishing |location=Melbourne |isbn=9781486312320 |pages=256 |url=https://www.publish.csiro.au/book/7924/}}</ref> The Murray cod is the largest exclusively freshwater fish in Australia, and one of the largest in the world. Other common names for Murray cod include '''cod''', '''greenfish''', '''goodoo''', '''Mary River cod''', '''Murray perch''', '''ponde''', '''pondi''' and '''Queensland freshwater cod'''.<ref name="FOA" />

The scientific name of Murray cod derives from an early Australian fish researcher [[Allan Riverstone McCulloch]] and the river from which the explorer [[Major Mitchell]] first scientifically described the species, the [[Peel River (New South Wales)|Peel River]].<ref name="FOA" />  This was for a number of years changed to ''M. peelii peelii'' to differentiate Murray cod from [[Mary River cod]], which were designated as a [[subspecies]] of Murray cod. However, as of 2010, Mary River cod have been raised to full species status (''M. mariensis''), thus Murray cod have reverted simply to ''M. peelii''.<ref name=Nocketal2010>{{Cite journal  | last = Nock | first = C. J.  | author2 = Elphinstone M. S.  | author3 = Rowland S. J.
  | author4 = Baverstock, P. R.  | name-list-style = amp  | title = Phylogenetics and revised taxonomy of the Australian freshwater cod genus, ''Maccullochella'' (Percichthyidae)  | journal = Marine and Freshwater Research  | volume = 61  | pages = 980–991  | year = 2010  | doi = 10.1071/MF09145  | issue = 9}}</ref>

Murray cod populations have declined severely since [[British colonisation of Australia|European colonisation]] of Australia due to a number of causes, including severe overfishing, river regulation, and habitat degradation and are now a listed threatened species. However, they once inhabited almost the entire [[Murray-Darling basin]], Australia's largest river system, in very great numbers.

A long-lived fish, adult Murray cod are [[carnivorous]] and eat crustaceans (shrimp, yabbies, crays), fish and freshwater mussels.<ref name=":1" /><ref name=":2">{{cite book |last1=Doyle |first1=Katherine |title=Can native Australian percichthyid fishes control invasive common carp (Cyprinus carpio)? |date=2012 |publisher=The University of Queensland |location=Brisbane}}</ref> The species exhibits a high degree of parental care for their [[Fish egg|eggs]], which are [[Spawn (biology)|spawned]] in the spring and are generally laid in hollow logs or on other hard surfaces. Murray cod are a popular angling target and [[aquaculture]] species. Often available through the aquarium trade, they are also a popular aquarium species in Australia.<ref name=nfacod/>
{{toc limit|3}}

==Description==
[[Image:Maccullochella peelii peelii.jpg|thumb|A Murray cod, displaying characteristic mottled green colouration.]]
The Murray cod is a large [[grouper]]-like fish with a deep, elongated body<ref name="CadwalladerBackhouse1983">
{{cite book
  | last = Cadwallader  | first = P. L.
  |author2=Backhouse, G. N.
  | title = A guide to the freshwater fish of Victoria
  | publisher = Government printers
  | year = 1983
  | location = Melbourne
  | isbn = 0-7241-8296-9}}
</ref> that is round in cross section. It has a broad, scooped head, and a large mouth lined with pads of very small, needle-like teeth. The jaws of the Murray cod are equal, or the lower jaw protrudes slightly.<ref name=Allen-et-al2002>
{{cite book
  | last = Allen  | first = G. R. |author2=Midgley, S. H. |author3=Allen M.
  | title = Freshwater Fishes of Australia
  | publisher = Western Australian Museum
  | year = 2002
  | location = Perth
  | pages = 194–195
  | isbn = 0-7307-5486-3}}
</ref><ref name="McDowall1996">
{{cite book
  | editor-last = McDowall
  | editor-first = R.
  |   title = Freshwater Fishes of south-eastern Australia
  | edition = Rev.
  | publisher = Reed Books
  | year = 1996
  | location = Sydney
  | pages = 158–160
  | isbn = 0-7301-0462-1}}
</ref><ref name=nfacod>
{{Cite web  | title = Murray cod  | website = Native Fish Australia  | url = http://www.nativefish.asn.au/cod.html  | access-date = 2007-09-28
  | url-status = dead  | archive-url = https://web.archive.org/web/20071010105433/http://www.nativefish.asn.au/cod.html  | archive-date = 2007-10-10
  }}</ref>

The spiny [[dorsal fin]] of Murray cod is moderate to low in height and is partially separated by a notch from the high, rounded soft dorsal fin.<ref name=McDowall1996/>  Soft dorsal, anal, and caudal (tail) fins are all large and rounded, and are dusky grey or black with distinct white edges.<ref name="CadwalladerBackhouse1983"/><ref name=nfacod/> The large, rounded pectoral fins are usually similar in colour to the flanks. The pelvic fins are large, angular, and set forward of the pectoral fins. The leading white-coloured rays on the pelvic fins split into two trailing white filaments,<ref name=McDowall1996/> while the pelvic fins themselves are usually a translucent white or cream, tending toward opacity in large fish.

Murray cod are white to cream on their ventral (belly) surfaces.<ref name=McDowall1996/><ref name=nfacod/> Their backs and flanks are usually yellowish-green to green, overlain with heavy darker green, but occasionally brown or black, mottling.<ref name=Allen-et-al2002/><ref name=McDowall1996/><ref name=nfacod/> The effect is a marbled appearance sometimes reminiscent of a leopard's markings. Colouration is related to water clarity;<ref name=nfacod/> colouration is intense in fish from clear water [[habitat]]s. Small to medium-sized Murray cod from clear-water habitats often have striking and very distinct colouration. Very large fish tend towards a speckled grey-green colouration.<ref name=trueman2007>
{{Cite web  | last = Trueman  | first = W. T.  | title = Some Recollections of Native Fish in the Murray-Darling System with Special Reference to the Trout Cod Maccullochella macquariensis  | publisher = Native Fish Australia  | date = 2007  | url = http://www.nativefish.asn.au/userfiles/files/Recollections_compressed.pdf  | access-date = 16 December 2018}}</ref>

===Size===
Murray cod are large fish, with adult fish regularly reaching {{convert|80|–|100|cm|in|abbr=on}} in length. Murray cod are capable of growing well over {{convert|1|m|ft|abbr=on}} in length and the largest on record was over {{convert|1.8|m|ft|abbr=on}} and about {{convert|113|kg|lb|abbr=on}} in weight.<ref name="McDowall1996"/><ref name="Rowland1989"/><ref name="Rowland2005"/>  Large breeding fish are rare in most wild populations today due to overfishing.<ref name=kearney&kildea2001>
{{Cite book
  | last = Kearney  | first = R. E.
  |author2=Kildea, M. A.
  | title = The status of Murray cod in the Murray-Darling Basin.
  | publisher = Department of Environment and Heritage (DEH)
  | year = 2001
  | url = http://www.environment.gov.au/water/publications/mdb/murray-cod.html
  | access-date = 2007-10-03 }}
</ref><ref name=NSW.Fish.unpubl.data>
{{Citation  | publisher = NSW Fisheries  | title = [unpublished data]}}</ref><ref name=Nicol-et-al2005>
{{cite conference
  | first = S.  | last = Nicol |author2=Todd, C. |author3=Koehn, J. D. |author4=Lieschke, J.
  | title = How can recreational angling regulations meet the multiple objectives for the management of Murray cod populations?
  | book-title = Management of Murray cod in the MDB. Statements, recommendations and supporting papers. Workshop, 3–4 June 2004, Canberra
  | year = 2005}}</ref><ref name=Stuart&Koehn2007>
{{cite journal
  | last = Stuart  | first = I.
  |author2=Koehn, J. D.
  | title =  Big cod do breed
  | journal = Freshwater Fishing Magazine
  | volume = 85
  | pages = 62–64
  | year = 2007 }}
</ref>

==Related species==
[[Image:Sizeable Murray cod.JPG|thumb|Murray cod push significant distances into [[upland (freshwater ecology)|upland]] river habitats.]]
Murray cod continue a pattern present in Murray-Darling native fish genera of speciation into [[Lowland (freshwater ecology)|lowland]] and specialist [[upland (freshwater ecology)|upland]] species: Murray cod are the primarily lowland species and the endangered [[trout cod]] are the specialist upland species. The pattern is slightly blurred in the cod species because, being adaptable and successful fish, Murray cod push significant distances into upland habitats, while the now endangered [[trout cod]] stray (or did stray, before their decline) well down the upland/lowland transition zone, which can be extensive in Murray-Darling Rivers. Nevertheless, the basic pattern of [[speciation]] into a primarily lowland species and a specialist upland species is present.<ref name=trueman2007/>

Murray cod, like a number of other Murray-Darling native fish species, have also managed to cross the [[Great Dividing Range]] at least once through natural [[river capture]] events, leading to several species and subspecies of coastal cod. The best known are [[eastern freshwater cod]] of the [[Clarence River (New South Wales)|Clarence River]] system in northern [[New South Wales]], and Mary River cod of the [[Mary River (Queensland)|Mary River]] system in south eastern [[Queensland]], both of which are endangered, but survive today. Coastal cod were also found in the [[Richmond River]] system in northern New South Wales and the [[Brisbane River]] system in southern Queensland, but are now extinct.<ref name=nfacod/><ref name=nswdf79r>
{{Cite journal
 |title=Profiles for species, populations & ecological communities: Eastern freshwater cod
 |journal=Priority Action Statement
 |publisher=NSW Fisheries
 |url=http://pas.dpi.nsw.gov.au/Species/Species_Profile.aspx?SpeciesListingID=3
 |access-date=2008-07-01
 |url-status=dead
 |archive-url=https://web.archive.org/web/20080723235215/http://pas.dpi.nsw.gov.au/Species/Species_Profile.aspx?SpeciesListingID=3
 |archive-date=2008-07-23
}}
</ref>

==Taxonomy==
In Mitchell's original description, he classified the fish as "Family, Percidae; Genus, Acerina; Subgenus, Gristes, Cuv. or Growler; Species, Gristes peelii mihi, or Cod-perch", observing "This fish may be identical with the fish described by MM. Cuvier and Valenciennes Volume 3 page 45 under the name of Gristes macquariensis: but it differs from their description…".<ref>Mitchell, Thomas Livingstone. ''Three Expeditions into the Interior of Eastern Australia …'' 2 ed., vol 1. [http://gutenberg.net.au/ebooks/e00035.html] Cuvier had placed the [[largemouth bass]] and [[Maccullochella macquariensis|blue nose cod]] into a single genus, ''Gristes'' (''Le Règne Animal…'', rev. ed., t. 2 (1829), p. 145 [https://www.biodiversitylibrary.org/item/99171#page/167/mode/1up] ), but the North American [[Black bass|black basses]] and Australian trout-cods are now considered unrelated.</ref>{{Rp|Jan 24}}

In the 1800s and early 1900s, commercial fishermen, recreational fishermen, riverside residents, and some fisheries scientists (e.g. Anderson, Stead, Langtry) distinctly recognised two species of cod in the southern Murray-Darling basin, Murray cod and trout cod or "blue nose cod". Taxonomically however, confusion abounded. Ignoring glaring differences in size at sexual maturity, and via some rather unscientific reasoning, some prominent fisheries scientists (e.g. Whitley) insisted on recognising only one species of cod—the Murray cod (then named ''Maccullochella macquariensis'', after an early Australian fish researcher with the surname McCulloch<ref name=mdbcnames>
{{Cite journal
 |title=Fish Names
 |journal=Basin Kids
 |publisher=Murray Darling Basin Commission
 |url=http://www.landmark.mdbc.gov.au/education/basinkids/basin_fish/Fish_Names.htm
 |access-date=2007-10-02
 |url-status=dead
 |archive-url=https://web.archive.org/web/20070831151522/http://www.landmark.mdbc.gov.au/education/basinkids/basin_fish/fish_names.htm
 |archive-date=2007-08-31
}}
</ref> and the Macquarie River in [[New South Wales]] where the [[holotype]] was captured<ref name=mdbcnames/>). Then, as trout cod declined into near extinction over the 1900s, the distinction between the two species was further eroded and finally questioned. In the 1970s, early genetic techniques confirmed that trout cod were a separate [[species]] and further showed that the original "Murray cod" specimen was in fact a trout cod. Following the rules of [[scientific classification]], the name ''M. macquariensis'' remained with the original specimen, now known to be the trout cod, and a new name, ''M. peelii'', for the Peel River<ref name=mdbcnames/> where the new holotype was captured, was coined for the Murray cod. Subsequently, two further cod were identified as separate species, the eastern freshwater cod (''M. ikei'') and the Mary River cod (''M. mariensis'').<ref name=Nocketal2010/><ref name=nfacod/>

==Range==
The Murray cod is named after the [[Murray River]], part of the Murray-Darling basin in eastern Australia, Australia's largest and most important river system, draining around 14% of the continent.<ref name=CadwalladerBackhouse1983/><ref name=mdbcstats>{{Cite web |title=Basin Statistics
 |publisher=Murray Darling Basin Commission |url=http://www.mdbc.gov.au/about/basin_statistics |access-date=2007-09-28 |url-status=dead
 |archive-url=https://web.archive.org/web/20070903055041/http://www.mdbc.gov.au/about/basin_statistics |archive-date=2007-09-03 }}</ref> The Murray cod's natural range encompasses virtually the whole Murray-Darling basin,<ref name=Allen-et-al2002/><ref name=McDowall1996/> particularly the lowland areas, and extending well into upland areas — to about {{convert|700|m|ft|abbr=on}} elevation in the southern half of the basin and to about {{convert|1000|m|ft|abbr=on}} in the northern half of the basin.<ref name=nfacod/>
[[Image:Maccullochella-peelii-dist.gif|thumb|Distribution of Murray cod<ref name=Allen-et-al2002/><ref name=McDowall1996/>]]
Consequently, Murray cod inhabit a remarkably wide variety of habitats, from cool, clear, fast-flowing streams with riffle-and-pool structure and rocky [[Substrate (marine biology)|substrates]] in upland areas to large, slow flowing, meandering rivers in the extensive alluvial lowland reaches of the Murray-Darling basin.<ref name="CadwalladerBackhouse1983"/><ref name="McDowall1996"/>
<ref name="Rowland1989">
{{Cite journal
  | last = Rowland | first = S. J.
  | title = Proceedings of the Linnean Society of New South Wales: Aspects of the history and fishery of the Murray cod, ''Macullochella peeli'' (Mitchell) (Percichthyidae)
  | journal = Proceedings of the Linnean Society of New South Wales
 | year = 1989|url=http://biostor.org/reference/68503
  | volume = 111
  | pages = 201–213}}
</ref><ref name="Rowland2005">{{Cite web |last=Rowland |first=S. J. |url=http://www.mdbc.gov.au/__data/page/641/5_Stuart_J._Rowland.pdf
 |title=Management of Murray cod in the MDB. Statements, recommendations and supporting papers: Overview of the history, fishery, biology and aquaculture of Murray cod (''Maccullochella peelii peelii''): Workshop, 3–4 June 2004, Canberra|place= Canberra |year=2005 |publisher=Murray Darling Basin Commission  |access-date=2007-10-04 |url-status=dead |archive-url=https://web.archive.org/web/20070829102559/http://mdbc.gov.au/__data/page/641/5_Stuart_J._Rowland.pdf |archive-date=2007-08-29}}</ref>
Murray cod have died out in many of their upland habitats, particularly in the southern Murray-Darling basin, due to a combination of [[overfishing]], [[siltation]], dams and [[weir]]s blocking migration, pollution from [[arsenic]]-based sheep-dips, [[mining]], and in some cases, introduced [[trout]] stockings, which causes competition between juvenile Murray cod and introduced [[trout]] species.<ref name=Rowland2005/><ref name="Rowland2020">
{{cite book
|last1=Rowland
|first1=S. J.
|title=The Codfather
|date=2020
|publisher=Optima Press
|location=Perth, Australia
|edition=First
}}
</ref>
<ref name="Kaminskas2022">
{{cite journal
|last1=Kaminskas
|first1=S.
|date=2022-02-22
|title=Alien fish ascendancy and native fish extinction: ecological history and observations on the Lower Goodradigbee River, Australia
|url=https://www.publish.csiro.au/PC/PC21048
|journal=Pacific Conservation Biology
|volume=29
|pages=38–73
|doi=10.1071/PC21048
|s2cid=247078783
|access-date=2022-05-03
|doi-access=free
}}
</ref>
Murray Cod have also been introduced into other [[drainage basin]]s, such as the Cooper Basin in Queensland.<ref name="Unmack">{{cite web |last1=Unmack |first1=Peter J. |title=Macullochella peelii peelii (Mitchell 1838) |url=https://www.desertfishes.org/australia/fish/maccpeel.html |website=Desert Fishes of Australia |access-date=9 May 2022}}
</ref>

==Age==
Murray cod are very long-lived, which is characteristic of many freshwater native fish in Australia.<ref name=nfacod/> Longevity is a survival strategy in variable Australian environment to ensure that most adults participate in at least one exceptional [[Spawn (biology)|spawning]] and recruitment event, which are often linked to unusually wet [[La Niña]] years and may only occur every one or two decades.<ref name=nfacod/> Murray cod are the most long-lived freshwater native fish in Australia.<ref name=CadwalladerBackhouse1983/> The oldest Murray cod aged yet was 48 years of age,<ref name="AndersonEtAl1992">{{cite journal  | last = Anderson  | first = J. R. |author2=Morison, A. K. |author3=Ray, D. J.
  | title = Age and growth of Murray cod, ''Maccullochella peeli'' (Perciformes: Percichthyidae), in the lower Murray-Darling Basin, Australia, from thin-sectioned otoliths  | journal = Australian Journal of Marine and Freshwater Research  | volume = 43  | pages = 983–1013  | year = 1992  | doi = 10.1071/MF9920983  | issue = 5 }}</ref> and the even larger specimens of years past leave little doubt that the species can reach considerably greater ages, of 70 years or more.<ref name="Rowland2005"/>

==Diet==
The Murray cod is the apex aquatic predator in the rivers of the Murray-Darling basin,<ref name="FOA" /> and will eat almost anything smaller than itself, including finned fishes such as smaller Murray cod, [[golden perch]], [[Bidyanus bidyanus|silver perch]], [[bony bream]], [[eel-tailed catfish]], [[western carp gudgeon]], and [[Australian smelt]] and introduced fish such as [[carp]], [[goldfish]], and [[European perch|redfin (English perch)]], as well as [[crustacean]]s such as [[common yabby|yabbies]], [[Atyidae|freshwater shrimp]], and [[Murray crayfish]]. Fish are eaten when abundant by mature Murray cod in lowland river and impoundment habitats<ref name=Ebner2006>, but crustaceans (shrimp, yabbies, crayfish) are likely the preferred diet under 'natural' river conditions, and mussels were an important food source, at least in the past.
{{cite journal
  | last = Ebner  | first = B.
  | title = Murray cod an apex predator in the Murray River, Australia
  | journal = Ecology of Freshwater Fish
  | volume = 15
  | pages = 510–520
  | year = 2006
  | doi = 10.1111/j.1600-0633.2006.00191.x
  | issue = 4 | bibcode = 2006EcoFF..15..510E
 }}
</ref> but crustaceans tend to dominate the diet under natural conditions, and freshwater mussels were commonly eaten in the past.<ref name=":1" /><ref name=":2" /> Murray cod have also been known to eat [[duck]]s, [[cormorant]]s, [[Chelidae|freshwater turtle]]s, [[Physignathus lesueurii|water dragon]]s, [[snake]]s, [[mice]], and [[frog]]s. The observations of the recreational fishermen fishing for Murray cod with surface lures at night reveal that the popular description of Murray cod as a [[Demersal zone|demersal]] [[ambush predator]] is only partially correct. While this behaviour is typical during the day, at night, Murray cod are active [[Pelagic zone|pelagic]] predators, venturing into shallow waters and frequently taking prey from the surface.<ref name=schultz2006>
{{Cite web
 |last=Schultz
 |first=N.
 |title=Flyrodding Murray cod by Neil Schultz
 |date=2006
 |publisher=Fishnet
 |url=http://www.fishnet.com.au/default.aspx?id=234&articleId=4192
 |access-date=2007-10-02
 |url-status=dead
 |archive-url=https://web.archive.org/web/20070924123128/http://www.fishnet.com.au/default.aspx?id=234
 |archive-date=2007-09-24
}}
</ref>

==Reproduction==
[[Image:Small Murray cod.JPG|thumb|A small Murray cod from a run in an upland river]]
Murray cod reach sexual maturity between four and six years of age, generally five years.<ref name=Rowland2005/><ref name=Rowland1998a>
{{cite journal
  | last = Rowland  | first = S. J.
  | title = Aspects of the reproductive biology of Murray cod, ''Maccullochella peelii peelii''
  | journal = Proceedings of the Linnean Society of New South Wales
  | volume =120
  | pages = 147–162|url=http://biostor.org/reference/68505
  | year = 1998 }}
</ref><ref name=Rowland1998b>
{{cite journal
  | last = Rowland  | first = S. J.
  | title = Age and growth of the Australian freshwater fish Murray cod, ''Maccullochella peelii peelii''
  | journal = Proceedings of the Linnean Society of New South Wales
  | volume = 120|url=http://biostor.org/reference/68506
  | pages = 163–180
  | year = 1998 }}
</ref>  Sexual maturity in Murray cod is dependent on age.<ref name=Rowland1998a/><ref name=Rowland1998b/> Therefore, roughly 70% of wild river Murray cod, with their slower growth rate, have reached sexual maturity by {{convert|50|cm|in|abbr=on}} in length. Wild Murray cod in impoundments like [[Lake Mulwala]], with their faster growth rates, do not reach sexual maturity until they are well over {{convert|60|cm|ft|abbr=on}} in length.<ref name=Rowland2005/><ref name=Rowland1998a/><ref name=Rowland1998b/> These data strongly indicate the 50-cm (20-in) size limit for Murray cod is inadequate and should be increased substantially to allow for a greater chance of reproduction before capture.

Large female Murray cod in the 15– to 35-kg (35– to 80-lb) range are the most important breeders because they produce the most [[Fish egg|eggs]] and for other reasons;<ref name=Rowland2005/> large females in most fish species are also important because they produce larger larvae with larger yolk sacs, and are also more experienced breeders that display optimal breeding behaviours.<ref name=Stuart&Koehn2007/><ref name=Trippel1995>
{{cite journal
  | last = Trippel  | first = E. A.
  | title = Age at Maturity as a Stress Indicator in Fisheries
  | journal = BioScience
  | volume = 45
  | pages = 759–771
  | year = 1995
  | doi = 10.2307/1312628
  | issue = 11
  | jstor = 1312628 }}
</ref><ref name=MarteinsdottirSteinarsson1998>
{{cite journal
  | last = Marteinsdottir  | first = G.
  |author2=Steinarsson, A.
  | title = Maternal influence on the size and viability of Iceland cod ''Gadus morhua'' eggs and larvae
  | journal = Journal of Fish Biology
  | volume = 52|doi=10.1111/j.1095-8649.1998.tb00969.x
  | pages = 1241–1258
  | year = 1998
  | issue = 6 | bibcode = 1998JFBio..52.1241M
 }}
</ref><ref name=MarteinsdottirBegg2002>
{{cite journal
  | last = Marteinsdottir  | first = G.
  |author2=Begg, G.A.
  | title = Essential relationships incorporating the influence of age, size and condition on variables required for estimation of reproductive potential in Atlantic cod ''Gadus morhua''
  | journal = Marine Ecology Progress Series
  | volume = 235
  | pages = 235–256
  | year = 2002
  | doi = 10.3354/meps235235 | bibcode = 2002MEPS..235..235M
 | doi-access = free
  }}
</ref> Such large females may also have valuable, successful genes to pass on.<ref name=Stuart&Koehn2007/> All of these factors mean the spawnings of large female fish have far higher larval survival rates and make far greater reproductive contributions than the spawnings of small female fish.<ref name=Stuart&Koehn2007/><ref name=Trippel1995/><ref name=MarteinsdottirSteinarsson1998/><ref name=MarteinsdottirBegg2002/> Not surprisingly, there is no truth to claim made by some recreational fishers that "large Murray cod don't breed".

Female Murray cod, upon first reaching sexual maturity, have egg counts of no more than 10,000. Very large female Murray cod can have egg counts as high as 80,000–90,000,<ref name=Rowland1989/> although a recent, very large 33-kg specimen yielded an egg count of 110,000 viable eggs.<ref name=Stuart&Koehn2007/> Egg counts in female Murray cod of all sizes are relatively low compared to many fish species.<ref name=Stuart&Koehn2007/><ref name=KoehnOConnor1990>
{{cite book
  | last = Koehn  | first = J. D.
  |author2=O'Connor, W. D.
  | title = Biological Information for Management of Native Fish in Victoria
  | publisher = Victorian Government Printing Office
  | location = Melbourne
  | year = 1990
  | isbn = 0-7306-0590-6}}
</ref>

Murray cod [[Spawn (biology)|spawn]] in spring, cued by rising water temperatures and increasing [[Photoperiodism|photoperiod]] (daylight length). Initially, fish biologists working with Murray cod considered spring floods and temperatures of {{convert|20|–|21|C|F}} to be necessary<ref name=KoehnOConnor1990/> and that spring flooding is critical for successful recruitment (i.e. survival to juvenile stages) of young cod by providing an influx of pelagic zooplankton and early life-stage [[invertebrate|macroinvertebrates]] off the flood plain into the main river channel for first feeding, but more recent research has shown Murray cod breed annually, with or without spring floods, and at temperatures as low as {{convert|15|°C|°F|abbr=on}}.<ref name=McDowall1996/><ref name=Rowland2005/><ref name=Rowland1998a/><ref name=Rowland1998b/><ref name=Humphries2005>
{{cite journal
  | last = Humphries  | first = P.
  | title = Spawning time and early life history of Murray cod, ''Maccullochella peelii peelii'' (Mitchell) in an Australian river
  | journal = Environmental Biology of Fishes
  | volume = 72
  | pages = 393–407
  | year = 2005
  | doi = 10.1007/s10641-004-2596-z
  | issue = 4 | s2cid = 23107553
 }}
</ref> Additionally, recent research has shown abundant epibenthic/epiphytic (bottom dwelling/edge clinging) prey in unflooded lowland rivers,<ref name=Humphries2005/><ref name=King2004>
{{cite journal
  | last = King  | first = A. J.
  | title = Density and distribution of potential prey for larval fish in the main channel of a floodplain river: Pelagic versus epibenthic meiofauna
  | journal = River Research and Applications
  | volume = 20
  | pages = 883–897
  | year = 2004
  | doi = 10.1002/rra.805
  | issue = 8 | bibcode = 2004RivRA..20..883K
 | s2cid = 26620366
 }}
</ref> traits in Murray cod larvae that should allow survival in a variety of challenging conditions,<ref name=King2005>
{{cite journal
  | last = King  | first = A. J.
  | title = Ontogenetic dietary shifts of fishes in an Australian floodplain river
  | journal = Marine and Freshwater Research
  | volume = 56
  | pages = 215–225
  | year = 2005
  | doi = 10.1071/MF04117
  | issue = 2 }}
</ref> and a significant proportion of Murray cod larvae feeding successfully in unflooded rivers.<ref name=King2005/><ref name=KaminskasHumphries2009>
{{cite journal
  | last = Kaminskas | first = S.
  |author2=Humphries, P.
  | title = Diet of Murray cod, (''Maccullochella peelii peelii'') (Mitchell) larvae in an Australian lowland river in low flow and high flow years
  | journal = Hydrobiologia
  | volume = 636
  | pages = 449–461
  | year = 2009
  | doi = 10.1007/s10750-009-9973-8| s2cid = 32045501
 }}
</ref>

Latest research has also shown that Murray cod in fact live their entire lifecycle within the main channel of the stream. Earlier ideas that Murray cod spawn on floodplains, or the larvae feed on floodplains, are incorrect. Murray cod breed in the main river channel or, in times of spring flood, the inundated upper portion of the main channel and tributary channels, but not on floodplains. Murray cod larvae feed within the main river channel or, in times of spring flood, on the inundated upper portion of the main channel and the channel/floodplain boundary, but not on the floodplain.<ref name=Koehn-in-prep>{{Citation  | last = Koehn | first =  J. D.  | title = In preparation}}</ref>{{better source needed|date=August 2023}}

Spawning is sometimes preceded by upstream or downstream movements.<ref>{{Cite journal |last=Koehn |first=J. D. |last2=McKenzie |first2=J. A. |last3=O’Mahony |first3=D. J. |last4=Nicol |first4=S. J. |last5=O’Connor |first5=J. P. |last6=O’Connor |first6=W. G. |date=2009 |title=Movements of Murray cod ( Maccullochella peelii peelii ) in a large Australian lowland river |url=https://onlinelibrary.wiley.com/doi/10.1111/j.1600-0633.2009.00375.x |journal=Ecology of Freshwater Fish |language=en |volume=18 |issue=4 |pages=594–602 |doi=10.1111/j.1600-0633.2009.00375.x |issn=0906-6691|url-access=subscription }}</ref> Radio-tracked Murray cod in the Murray River have moved up to {{convert|120|km|mi|abbr=on}} upstream to spawn, before returning to exactly the same snag from where they departed, an unusual homing behaviour in a freshwater fish.<ref name=Koehn-in-prep/> Decades of observations by recreational and commercial fishermen suggest such spring spawning movements are common across the Murray cod's geographical range.<ref name=nfacod/> Spawning is initiated by pairing up and courtship rituals. During the courtship ritual a spawning site is selected and cleaned — hard surfaces such as rocks in upland rivers and impoundments, and logs and occasionally clay banks in lowland rivers, at a depth of {{convert|2|–|3|m|ft}}, are selected. The female lays the large adhesive eggs as a mat on the spawning surface, which the male fertilises. The female then leaves the spawning site. The male remains to guard the eggs during incubation, which takes six to 10 days (depending on water temperature), and to guard the hatched larvae for a further week or so until they disperse. Larvae disperse from the nest site by drifting in river currents at night, and continue this behaviour around four to seven days.<ref name=Rowland2005/><ref name=Rowland1998a/><ref name=Rowland1998b/><ref name=Humphries2005/><ref name=Lake1967>
{{cite journal
  | last = Lake  | first = J. S.
  | title = Rearing experiments with five species of Australian freshwater fishes. I. Inducement to spawning
  | journal = Australian Journal of Marine and Freshwater Research
  | volume = 18
  | pages = 137–153
  | year = 1967
  | doi = 10.1071/MF9670137
  | issue = 2 }}
</ref><ref name=Cadwallader1977>
{{Cite journal
  | editor-last = Cadwallader | editor-first = P. L.
  | title = J. O. Langtry's 1949–50 Murray River Investigations
  | journal = Fisheries and Wildlife Paper
  | publisher = Ministry for Conservation, Victoria
  | year = 1977}}
</ref><ref name=Rowland1983>
{{cite journal
  | last = Rowland  | first = S. J.
  | title = Spawning of the Australian freshwater fish Murray cod ''Maccullochella peeli'' (Mitchell), in earthen ponds
  | journal = Journal of Fish Biology
  | volume = 23
  | pages = 525–534
  | year = 1983
  | doi = 10.1111/j.1095-8649.1983.tb02932.x
  | issue = 5 | bibcode = 1983JFBio..23..525R
 }}
</ref><ref name=KoehnHarrington2005>
{{cite journal
  | last = Koehn  | first = J. D.
  |author2=Harrington, D. J.
  | title = Collection and distribution of early life stages of the Murray cod (''Maccullochella peelii peelii'') in a regulated river
  | journal = Australian Journal of Zoology
  | volume = 53
  | pages = 137–144
  | year = 2005
  | doi = 10.1071/ZO04086
  | issue = 3 }}
</ref> During this dispersal process, larvae simultaneously absorb the remainder of their yolk sac and begin to feed on small, early life-stage [[invertebrate|macroinvertebrates]] and epibenthic/epiphytic (bottom dwelling/edge clinging) microinvertebrates.<ref name=King2005/><ref name=KaminskasHumphries2009/> It may be that Murray cod are the first freshwater fish identified as having long-term pair-bonding in its repertoire of [[Animal sexual behaviour#Mating systems|mating strategies]] in the wild.<ref>{{cite journal |author1=Couch AJ |author2=Dyer FJ |author3=Lintermans M. |title=Multi-year pair-bonding in Murray cod (''Maccullochella peelii'') |journal=PeerJ |date=2020 |volume=8:e:e10460 |pages=e10460 |doi=10.7717/peerj.10460 |pmid=33354425 |pmc=7733648 |doi-access=free }}</ref>

The relationship between river flows and Murray cod recruitment are more complex than first thought, and in less regulated rivers, Murray cod may be able to recruit under a range of conditions including stable low flows. (Significant recruitment of Murray cod in low-flow conditions in less regulated lowland rivers has now been proven.) This information also suggests that nonriver-regulation-related causes of degradation are playing a larger role in the survival and recruitment of Murray cod larvae than first thought; competition from extremely large numbers of invasive [[carp]] larvae are negatively affecting the survival and recruitment of Murray cod larvae to a much greater degree than first thought;<ref name=Tonkin-et-al2006>
{{cite journal
  | last = Tonkin  | first = D. Z. |author2=Humphries, P. |author3=Pridmore, A. P.
  | title = Ontogeny of feeding in two native and one alien fish species from the Murray-Darling Basin, Australia
  | journal = Environmental Biology of Fishes
  | volume = 76
  | pages = 303–315
  | year = 2006
  | doi = 10.1007/s10641-006-9034-3
  | issue = 2–4 | bibcode = 2006EnvBF..76..303T | s2cid = 998756 }}
</ref> and that decades of overfishing is playing a far larger role in the current state of Murray cod stocks, through depletion of spawning adults, than first thought.<ref name=kearney&kildea2001/>

These findings do not mean that river regulation and water extraction have not had adverse effects on fish stocks. Rather, river regulation has been a major factor in the decline of Murray cod and other native fish.<ref name=Allen-et-al2002/> Thermal pollution is also a major problem, evidence indicates strong Murray cod recruitment events (which may be important for sustaining Murray cod populations over the long term) can result from spring flooding, and the health of Australian lowland [[river ecosystem]]s generally rely on periodic spring flooding.<ref name=kearney&kildea2001/><ref name=King_Env._Flow_2008>
{{cite journal
  | last = King | first = A. J. |author2=Tonkin, Z. |author3=Mahoney, J.
  | title = Environmental flow enhances native fish spawning and recruitment in the Murray River, Australia
  | journal = River Research and Applications
  | volume = 25
  | pages = 1205–1218
  | year = 2008
  | doi = 10.1002/rra.1209
  | issue = 10| s2cid = 38777514 }}
</ref> Also, due to the regulation of most of the rivers in the Murray-Darling River system, mainly for [[irrigation]] purposes, only exceptional spring floods manage to "break free". The long-term viability of wild Murray cod, other native fish species and river ecosystems, in the face of this fact, are of great concern.<ref name=kearney&kildea2001/>

==Conservation==
===History===
Murray cod were originally the most common large native fish in the Murray-Darling basin. Contrary to some fishery department literature, the first serious declines in Murray cod were caused by overfishing. In the latter half of the 1800s and the early 1900s, Murray cod were caught in large numbers by both commercial and recreational fishermen. For example, one commercial fishing operation commenced on the Murray River near [[Echuca]] in 1855, targeting Murray cod over hundreds of kilometres of river, and yet within eight years, grave concerns over the sustainability of this operation, and complaints about the near-absence of Murray cod in their heavily fished grounds, were being raised in the main state newspaper, ''The Argus''.<ref name=Humphries_Winemiller_2009>{{cite journal |last=Humphries |first=P.
 |author2=Winemiller, K. O. |title=Historical Impacts on River Fauna, Shifting Baselines, and Challenges for Restoration |journal=BioScience
 |volume=59 |pages=673–684 |year=2009 |url=https://academic.oup.com/bioscience/article/59/8/673/256074|issue=8| doi= 10.1525/bio.2009.59.8.9|s2cid=3731197 |url-access=subscription }}</ref> Yet fishing effort continued to increase in the region, so in the late 1880s and early 1890s, between 40,000 and 150,000&nbsp;kg of mostly Murray cod (between 7,500 and 27,000 fish, at an average weight of 5.5&nbsp;kg) were caught near Echuca.<ref name=Humphries_Winemiller_2009/> Similarly, in 1883, more than 147,000&nbsp;kg of Murray cod were sent to Melbourne from just one river town (Moama).<ref name=Rowland1989/> By the 1920s Murray cod had been overfished to the point where large-scale commercial fishing operations were no longer feasible.<ref name=Rowland1989/><ref name=Rowland2005/> Recreational fishermen took similarly excessive hauls during this era, using rods and reels, handlines, setlines, drum nets, gill nets, and even explosives, with hauls often either wasted or illegally sold. Perhaps this extreme overfishing and its impacts of wild Murray cod stocks is best summarised by a short article in the ''Register News'' (a South Australian newspaper) in 1929:

<blockquote>''In [the last] 29 years 26,214,502 lbs (nearly 11,703 tons) [11,915,683 kg] of Murray cod has been eaten by the people of Melbourne. The Superintendent of Markets (Mr G. B. Minns) included these figures in a statement he made today pointing out that the supply was declining. In 1918, the peak year, {{convert|2,229,024|lb|kg|abbr=on|disp=sqbr}} was received at the market, but since 1921, when {{convert|1,101,520|lb|kg|abbr=on|disp=sqbr}} was sent to Melbourne, supply has decreased. Last year [1928] it was only {{convert|551,040|lb|kg|abbr=on|disp=sqbr}}.''<ref name=Register_News>{{cite news|last=Anon|title=Less Murray Cod Sent to Melbourne — Supply Decreased To Half-Million Pounds In Year|url=https://trove.nla.gov.au/newspaper/article/53459650?searchTerm=less%20murray%20cod%20sent%20to%20Melbourne&searchLimits=|access-date=11 July 2011|newspaper=The Register News-Pictorial (Adelaide, South Australia)|date=25 May 1929}}</ref></blockquote>

Twenty years later, the aquatic ecologist J. O. Langtry criticised the heavy fishing pressure, in the form of both uncontrolled small-scale commercial fishing and rampant [[illegal fishing]], which he found in all reaches of the Murray River he investigated 1949–1950.<ref name=Cadwallader1977/>

A thorough reading of historical newspaper articles and historical government reports reveals that the history of wild Murray cod between the mid–1800s and the mid–1900s was one of citizen agitation, government inaction, and ongoing stock decline. For decades, riverside residents, commercial fishermen, recreational fishermen, local fisheries inspectors, fish retailers, and others agitated in newspapers and other fora about the declining Murray cod stocks, to be met in turn either with government denials, or conversely, with various ineffective inquiries into Murray cod stocks and fisheries, and various ineffective control measures. Debate about excessive fishing pressure, number of fishermen, number of nets, net mesh size, bag limits, minimum size limits and take of small cod, closed seasons and the taking of spawning cod full of eggs during spring, and other sundry issues, continued without resolution. Fishing regulations were either not amended, or amended and largely unenforced and completely ignored. Heavy commercial, recreational and [[illegal fishing]] pressure continued. The end result was a Murray cod population, initially abundant, continually fished down until in the early to mid 20th century a number of other factors such as river regulation (listed below) emerged to drive the species even further into decline. All of these drivers of decline left this iconic Australian fish in a perilous situation. There are now concerns for the long-term survival of wild Murray cod populations.<ref name=kearney&kildea2001/><ref name=Koehn2004/><ref name="codwatch25">Victorian Department of Sustainability and Environment, 2004, ''Codwatch Newsletter Number 25'', [http://www.greenhouse.vic.gov.au/CA256F310024B628/0/C95F6E2F115D3706CA2571480003EB28/$File/Codwatch+25+November+2004.pdf]{{dead link|date=December 2011}}, Retrieved 28 September 2007</ref>

===Status===
[[Image:Murray_cod_1800_lbs_Renmark_1898.jpg|thumb|An example of extreme overfishing of Murray cod in the late 1800s, which caused the first strong declines in the species. Such catches were typical for the period.]]
Since 3 July 2003 and {{as of|August 2023|lc=yes}}, the Murray cod is listed as a [[vulnerable species]] under the [[EPBC Act]] (''Environment Protection and Biodiversity Conservation Act 1999''). It is listed as a species of Least Concern on the [[IUCN Red List of Threatened Species]], but under state legislation in both [[South Australia]] and [[Victoria, Australia|Victoria]], it is an [[endangered species]].<ref name=sprat/>

A study published in ''[[Biological Conservation (journal)|Biological Conservation]]'' in March 2023 listed 23 species which the authors considered to no longer meet the criteria as threatened species under the EPBC Act, including the Murray cod.<ref name=woinarski2023>{{cite journal | last1=Woinarski | first1=John C.Z. | last2=Garnett | first2=Stephen T. | last3=Gillespie | first3=Graeme | last4=Legge | first4=Sarah M. | last5=Lintermans | first5=Mark | last6=Rumpff | first6=Libby|display-authors=2 | title=Lights at the end of the tunnel: The incidence and characteristics of recovery for Australian threatened animals | journal=Biological Conservation | publisher=Elsevier BV | volume=279 | year=2023 | issn=0006-3207 | doi=10.1016/j.biocon.2023.109946 | page=109946| doi-access=free | bibcode=2023BCons.27909946W }}</ref> The team, led by John Woinarski of [[Charles Darwin University]] looked at all species listed as threatened under the act in 2000 and 2022. The Murray cod was the only fish on the list,<ref>{{cite web | title=Researchers find 26 Australian species recovered from the brink of extinction | website=ABC News | date=24 February 2023 | url=https://www.abc.net.au/news/2023-02-24/australian-animals-no-longer-meet-criteria-as-threatened-species/102020276 | access-date=23 August 2023}}</ref> and the reason for their assessment was given as "Actual recovery over the period 2000–2022, from long period of decline".<ref name=woinarski2023/>

===Threats===
====Overfishing====
While extremely severe commercial and recreational overfishing in the 1800s and the early 1900s caused the first strong declines of Murray cod, [[overfishing]] by recreational fishermen, aided by inadequate fishing regulations, continues today and remains an extremely serious threat to Murray cod. The current size limit of 60&nbsp;centimetres in most states is inadequate now that scientific studies have documented average size at sexual maturity in Murray cod.<ref name=Nicol-et-al2005/> This and catch data and computer modelling exercises<ref name=Nicol-et-al2005/> on wild Murray cod stocks indicate measures such as raising the size limit to 70&nbsp;centimetres and reducing the bag and possession limits from 2 and 4 fish respectively to 1 fish are urgently needed to maintain the long-term viability of wild Murray cod populations. As of November 2014, the NSW Department of Fisheries has introduced a maximum size limit of 75&nbsp;cm for Murray Cod to provide protection for large breeding fish, as well as a new minimum size limit of 55&nbsp;cm.

Although angler effects are sometimes disregarded in the overall picture today, recent population studies have shown that while all year classes are well represented up to the minimum legal angling size (now 60&nbsp;centimetres in most states), above that size, numbers of fish are dramatically reduced almost to the point of non-existence in many waters.<ref name=Nicol-et-al2005/><ref name=Koehn2004/> Some emphasis has been made of the results of two small surveys which suggested a majority of Murray cod are released by anglers. However, there are valid questions as to the representativeness of these surveys: these surveys do not explain the dramatic disappearance of large numbers of young Murray cod at exactly the minimum size limit, and most importantly, any emphasis on these surveys miss the fundamental point — as a large, long-lived species with relatively low fecundity and delayed sexual maturity wild Murray cod populations are extremely vulnerable to overfishing, even with only modest angler-kill.<ref name=Nicol-et-al2005/><ref name=Koehn2004/> A tightening of fishing regulations for wild Murray cod, as referred to above, and a switch by fishermen to a largely [[catch and release]] approach for wild Murray cod would alleviate this problem.<ref name=Nicol-et-al2005/> Recognising these issues, in late 2014 the New South Wales and Victorian fishery departments amended their regulations so that a slot limit of 55 to 75&nbsp;cm now applies in these states. (i.e. only Murray cod between 55 and 75&nbsp;cm may be taken; those above and below this size range or "slot" must be released.) This measure should have positive effects for the Murray cod population by protecting and increasing the proportion of large breeding Murray cod.

Another issue is that Murray cod caught and released in winter, while developing their eggs, or in spring prior to spawning, resorb their eggs and do not spawn.<ref name=Rowland2005/><ref name=Lake1967/><ref name=Rowland1988>{{cite journal  | last = Rowland  | first = S. J.  | title = Hormone-induced spawning of the Australian freshwater fish Murray cod, ''Maccullochella peeli'' (Mitchell) (Percichthyidae)  | journal = Aquaculture  | volume = 70  | pages = 371–389  | year = 1988  | doi = 10.1016/0044-8486(88)90121-4  | issue = 4 | bibcode = 1988Aquac..70..371R }}</ref> This may be a minor issue compared to some of the other threats facing Murray cod, nevertheless, concerned fishermen try to avoid catching wild Murray cod at these times.<ref name=nfacod/> At this point in time a closed season is in place for the spring spawning period, during which anglers are not allowed to target Murray cod, even on a catch and release basis.

====Effects of river regulation====
The Murray River and southern tributaries originally displayed a pattern of high flows in winter, high flows and floods in spring, and low flows in summer and autumn. The breeding of Murray cod and other Murray-Darling native fish was adapted to these natural flow patterns. River regulation for irrigation has reversed these natural flow patterns, with negative effects on the breeding and recruitment of Murray cod. The Murray and most southern tributaries now experience high [[irrigation]] flows in summer and autumn and low flows in winter and spring. Small and medium floods including the once annual spring flood-pulse have been completely eliminated.<ref name=Allen-et-al2002/><ref name=McDowall1996/><ref name=Koehn2004>
{{Cite web |last=Koehn |first=J. D. |title=Threats to Murray cod |publisher=Murray Darling Basin Commission |date=2004 |url=http://www.mdbc.gov.au/__data/page/641/4_John_D._Koehn.pdf |access-date=4 October 2007 |url-status=dead |archive-url=https://web.archive.org/web/20070829102517/http://mdbc.gov.au/__data/page/641/4_John_D._Koehn.pdf |archive-date=29 August 2007}}</ref><ref name=sharing>{{cite book  | title = Sharing the Murray
  | publisher = Murray River Entitlements Committee  | year = 1997  | isbn = 0-7306-6797-9}}</ref>

It is estimated that flows at the river mouth by 1995 had declined to only 27% of natural outflows.<ref name=mdbcaudit1995>{{cite book |url=http://www.mdbc.gov.au/__data/page/101/WAM-Report-2004-05.pdf |title=Water Audit Monitoring Report 2004/05 |author=Murray-Darling Basin Commission| author-link=Murray-Darling Basin Commission|date=June 2006|isbn=1-921-038-93-4 |access-date=2007-09-28 |url-status=dead |archive-url=https://web.archive.org/web/20060906154918/http://www.mdbc.gov.au/__data/page/101/WAM-Report-2004-05.pdf |archive-date=2006-09-06 }}, retrieved 28 September 2007</ref> The probability of the bottom end of the Murray experiencing drought-like flows had increased from 5% under natural conditions to 60% by 1995.<ref name=mdbcaudit1995/>

[[Thermal pollution]] is the artificial reduction in water temperatures, especially in summer and autumn, caused when frigid water is released from the bottom of reservoirs for irrigation demands. Such temperature suppression typically extends several hundred kilometres downstream. Thermal pollution inhibits both the breeding of Murray cod and the survival of Murray cod larvae, and in extreme cases inhibits even the survival of adult Murray cod.<ref name=nfacod/>

The rare floods that do break free of the dams and weirs of the Murray-Darling system have their magnitude and duration deliberately curtailed by river regulators. Increasing research indicates this management practice is very harmful and drastically reduces the general [[ecosystem]] benefits and breeding and recruitment opportunities for Murray cod and other Murray-Darling native fish species these now rare floods can provide.<ref name=Allen-et-al2002/><ref name=McDowall1996/><ref name=Koehn2004/><ref name=sharing/>

====Blackwater events====
Blackwater events are emerging as a very serious threat to wild Murray cod stocks in lowland river reaches. Blackwater events occur when floodplains and ephemeral channels accumulate large quantities of [[leaf litter]] over a number of years and are then finally inundated in a flood event. The leaf litter releases large quantities of dissolved organic carbon, turning the water a characteristic black colour and inducing a temporary explosion in bacterial numbers and activity, which in turn consume dissolved oxygen, reducing them to levels harmful or fatal to fish. (Fish essentially asphyxiate.) Water temperature is a critical regulator of blackwater events as warmer water temperatures increase bacterial activity and markedly reduce the intrinsic oxygen carrying capacity of water; events that may be tolerable for fish in winter or early spring may be catastrophic in late spring or summer due to the increase in water temperature.<ref name="Whitworth et al. 2012">
{{Cite journal
  | last = Whitworth | first = K. L. |author2=Baldwin, D. S. |author3=Kerr, J. L.
  | title = Drought, floods and water quality: Drivers of a severe hypoxic blackwater event in a major river system (the southern Murray–Darling Basin, Australia)
  | journal = Journal of Hydrology
  | volume = 450–451
  | pages = 190–198
  | year = 2012
  | doi = 10.1016/j.jhydrol.2012.04.057| bibcode = 2012JHyd..450..190W }}
</ref>

Blackwater events are often described as "natural" events—while there are some historical records of relatively severe events in smaller, more ephemeral systems (e.g. lower Lachlan, upper Darling), there is no record of severe events in the Murray River and its largest southern tributaries before water extraction and river regulation. In the Murray and large southern tributaries, very severe large-scale blackwater events are a relatively new but recurring phenomenon and appear to be an effect of river regulation curtailing the winter/spring flood events that formerly swept [[leaf litter]] away annually, exacerbated by long-term declines in rainfall and recurring prolonged drought events.<ref name="Hladyz et al. 2011">
{{Cite journal
  | last = Hladyz | first = S. |author2=Watkins, S. C. |author3=Whitworth, K. L. |author4=Baldwin, D. S.
  | title = Flows and hypoxic blackwater events in managed ephemeral river channels
  | journal = Journal of Hydrology
  | volume = 401
  | pages = 117–125
  | year = 2011
  | doi = 10.1016/j.jhydrol.2011.02.014
  | issue = 1–2| bibcode = 2011JHyd..401..117H }}
</ref>

Flood events in 2010 and 2012 following the prolonged Millennium Drought (1997–2009) induced very severe blackwater events; while formal studies of these events were limited due to the relatively rapid response times required and logistical difficulties,<ref name="King et al. 2012">
{{Cite journal
  | last = King | first = A. J. |author2=Tonkin, A. |author3=Lieschke, J.
  | title = Short-term effects of a prolonged blackwater event on aquatic fauna in the Murray River, Australia: considerations for future events
  | journal = Marine and Freshwater Research
  | volume = 63
  | pages = 576–586
  | year = 2012
  | doi = 10.1071/MF11275
  | issue = 7 }}
</ref>
angler photographs and observations of extraordinary numbers of dead Murray cod during these events and plunging catch rates after these events show they induced extremely heavy Murray cod mortalities along extensive tracts of the Murray River.

====Physical barriers to fish movement====
Dams, [[weir]]s and other instream barriers block the migration of adult and juvenile Murray cod and prevent recolonisation of habitats and maintenance of isolated populations.<ref name=nfacod/> Additionally, recent study has proven approximately 50% of Murray cod larvae are killed when they pass through undershot weirs.<ref name=Baumgartner-et-al2006>
{{Cite journal
  | last = Baumgartner  | first = L. J. |author2=Reynoldson, N. |author3=Gilligan, D. M.
  | title = Mortality of larval Murray cod (''Maccullochella peelii peelii'') and golden perch (''Macquaria ambigua'') associated with passage through two types of low-head weirs
  | journal = Marine and Freshwater Research
  | volume = 57
  | pages = 187–191
  | year = 2006
  | doi = 10.1071/MF05098
  | issue = 2 }}
</ref>

====Habitat degradation / siltation====
Hundreds of thousands, perhaps more than a million, submerged timber "[[snags]]", mainly [[River Red Gum]], have been removed from lowland reaches of the Murray-Darling basin over the past 150 years.<ref name=MacNally-et-all2002>
{{Cite journal
  | last = MacNally  | first = R. |author2=Parkinson, A. |author3=Horrocks, G. |author4=Young, M.
  | title = Current Loads of Coarse Woody Debris on Southeastern Australian Floodplains: Evaluation of Change and Implications for Restoration
  | journal = Restoration Ecology
  | volume = 10
  | issue = 4
  | pages = 627–635
  | year = 2002
  | doi = 10.1046/j.1526-100X.2002.01043.x | bibcode = 2002ResEc..10..627M | s2cid = 84135006 }}
</ref> The removal of such a vast number of snags has had devastating impacts on Murray cod and river ecosystems. Snags are critical habitats and spawning sites for Murray cod. Snags are also critical for the functioning of lowland river ecosystems — as one of the few hard [[Substrate (marine biology)|substrates]] in lowland river channels composed of fine silts snags are crucial sites for [[biofilm]] growth, [[macroinvertebrate]] grazing and general in-stream productivity.<ref name=Koehn2004/><ref name=MacNally-et-all2002/>

Vegetation clearing and cattle trampling river banks create severe [[siltation]], which fill in pools, degrade river ecosystems and make rivers and streams uninhabitable for Murray cod.<ref name=McDowall1996/> This is exacerbated by removal of [[riparian]] (riverbank) vegetation which causes siltation and degrades river ecosystems in many ways.<ref name=nfacod/>

====Introduced carp====
There is serious competition for food between larval/early juvenile introduced carp and larval/early juvenile native fish.<ref name=Tonkin-et-al2006/> Introduced carp dominate the fish [[fauna]]s of lowland Murray-Darling rivers; the sheer amount of [[Biomass (ecology)|biomass]] carp now take up, and the large numbers of larvae carp produce, causes serious negative effects on river ecosystems and native fish.<ref name=Tonkin-et-al2006/> Carp are the main vector of the introduced ''[[Lernaea]]'' parasite (''[[Lernaea cyprinacea]]'') and serious vectors of the introduced Asian fish tapeworm (''[[Bothriocephalus acheilognathi]]'').

[[File:Lernaea parasite on a Murray cod.jpg|thumbnail|''Lernaea'' parasite on a murray cod]]

====Introduced pathogens====
Murray cod have soft skin and very fine scales that leave them particularly vulnerable to infection from exotic diseases and parasites. The following exotic diseases and parasites all seriously affect wild Murray cod; all have been introduced by imports of exotic fish.<ref name="Kaminskas 2020">{{cite journal|first1=S.|last1=Kaminskas|year=2020|title=Alien pathogens and parasites impacting native freshwater fish of southern Australia: a scientific and historical review|journal=Australian Zoologist|volume=41 |issue=4 |pages=696–730 |doi=10.7882/AZ.2020.039|s2cid=230643061 |doi-access=free}}</ref> ''Chilodonella'' is a single-celled, parasitic [[protozoa]] that infects the skin of Murray cod and has caused a number of serious kills of wild Murray cod.<ref name="Rowland and Ingram, 1991"/><ref name="Kaminskas 2020"/> ''[[Saprolegnia]]'' is a fungus-like oomycete or "water mould" that frequently infects Murray cod eggs and the skin of Murray cod that have been roughly handled through poor [[catch and release|catch and release technique]].<ref name="Rowland and Ingram, 1991"/><ref name="Kaminskas 2020"/> (It is essential that Murray cod intended for release only touch cool wet surfaces and are '''not''' put down on any hard, dry, rough or hot surfaces, e.g. boat gunwales, boat floors, dry grass, dry rocks, gravel banks, dry towels or mats, etc. Hands should also be wetted before touching them. They must not be hung vertically by the mouth or gill covers.) Wild Murray cod populations across their range suffer extremely severe infestations of ''Lernaea'' or "anchor worm", a parasitic [[copepod]] vectored by introduced [[carp]] and that burrows into the skin of Murray cod.<ref name="Rowland and Ingram, 1991">{{cite book|author1=Rowland SJ|author2=Ingram BA|title = Diseases of Australian native freshwater fishes with particular emphasis on the ectoparasitic and fungal diseases of Murray cod (Maccullochella peeli), golden perch (Macquaria ambigua) and silver perch (Bidyanus bidyanus)|publisher =NSW Fisheries, Sydney.|year =1991}}</ref><ref name="Kaminskas 2020"/><ref name="NSW Rivers Survey">{{cite book|author1=Harris JH|author2=Gehrke PC|title = Fish and Rivers in Stress — The NSW Rivers Survey|publisher =NSW Fisheries Conservation Office, Cronulla, Sydney|year =1997}}</ref> ''Lernaea'' puncture wounds are often secondarily infected by bacteria.<ref name="Khalifa and Post, 1976">{{cite journal|last1=Khalifa|first1=KA|last2=Post|first2=G|year=1976|title= Histopathological effect of Lernaea cyprinacea (a copepod parasite) on fish|journal= The Progressive Fish-Culturist|volume=38|issue=2|pages=110–113|doi=10.1577/1548-8659(1976)38[110:heolca]2.0.co;2}}</ref><ref name="Berry et al., 1991">{{cite journal|last1=Berry|first1=CR|last2=Babey|first2=GJ|last3=Shrader|first3=T|year=1991|title= Effect of Lernaea cyprinacea (Crustacea: Copepoda) on stocked rainbow trout (Oncorhynchus mykiss)|journal=Journal of Wildlife Diseases|volume=27|issue=2|pages=206–213|doi=10.7589/0090-3558-27.2.206|pmid=2067042|s2cid=28800550|doi-access=free}}</ref> Severe ''Lernaea'' infestations probably causes the death of many more adult Murray cod than commonly recognised.<ref name="Goodwin, 1999">{{cite journal|last1=Goodwin|first1=AE|year=1999|title= Massive Lernaea cyprinacea infestations damaging the gills of channel catfish Ictalurus punctatus polycultured with bighead carp Hypophthalmichthys nobilis|journal= Journal of Aquatic Animal Health|volume=11|issue=4|pages=406–408|doi=10.1577/1548-8667(1999)011<0406:mlcidt>2.0.co;2}}</ref><ref name="Kaminskas 2020"/> Ebner<ref name=Ebner2006/> reports a young adult Murray cod seemingly killed by severe ''Lernaea'' infestation.

===Conservation measures===
State government fisheries departments support Murray cod populations by stocking with hatchery-bred fish, especially in man-made lakes.<ref name=Koehn2004/> Important issues affecting restoration of cod populations, such as the need for spring floods and excessive angler take, are slowly being acknowledged <ref name=Koehn2004/> but are yet to be definitely addressed.<ref name=McKeller2004>{{cite web |last=McKelleher
 |first=R. |title=An outline of the threatened species listing process under the Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act) |url=http://www.mdbc.gov.au/__data/page/641/6_Rob_McKelleher.pdf |publisher=Department of Environment and Heritage (DEH) |access-date=3 October 2007 |url-status=dead |archive-url=https://web.archive.org/web/20120325070451/http://www2.mdbc.gov.au/__data/page/641/6_Rob_McKelleher.pdf |archive-date=25 March 2012}}</ref> Other concerns such as the stocking of Murray cod in areas where [[trout cod]] (''M. macquariensis'') are recovering encourages [[hybridisation (biology)|hybridisation]] and needs consideration for future restocking programs.<ref>{{cite journal |last1=Couch|first1=Alan|author2=Peter J. Unmack|author3=Fiona J. Dyer|author4=Mark Lintermans|title=Who's your mama? Riverine hybridisation of threatened freshwater Trout Cod and Murray Cod|journal=PeerJ|date=27 October 2016|volume=4:e2593|pages=e2593|doi= 10.7717/peerj.2593|pmc=5088581
 |pmid=27812407 |doi-access=free }}</ref>

[[Image:Tocumwal Big Cod.JPG|thumb|Statue of a Murray cod in [[Tocumwal]], [[New South Wales]]]]

==Relationship with humans==
Murray cod play a very important role in the mythology of many [[Australian Aborigines|Aboriginal]] tribes in the Murray-Darling basin,<ref name=Allen-et-al2002/> and for some tribes, particularly those living along the Murray River, Murray cod were the icon species.<ref>[[David Unaipon|Unaipon, D.]] (2001) ''Legendary Tales of the Australian Aborigines'', p. 17, The Miegunyah Press, Melbourne. {{ISBN|0-522-85246-7}}.</ref> The [[mythology|myth]]s of these tribes describe the creation of the Murray River by a gigantic Murray cod fleeing down a small creek to escape from a renowned hunter. In these myths, the fleeing Murray cod enlarges the river and the beating of its tail create the bends in it. The cod is eventually speared near the terminus of the Murray River, chopped into pieces, and the pieces thrown back into the river. The pieces become all the other fish species of the river. The cod's head is kept intact, told to "keep being Murray cod", and also thrown back into the river.<ref name="Rowland1989"/><ref name="Rowland2005"/>

Murray cod continue to play important roles in the culture of First Nations Peoples along the Murray and Darling rivers and the Murray-Darling Basin overall. <ref name=":1" />

== Aquaculture ==
The Murray cod is renowned as a good-tasting fish for eating. In recent years, despite the decline in the wild population, farmed fish are being harvested.<ref name=":0">{{Cite web|title=Murray Cod - GoodFish Australia's Sustainable Seafood Guide|url=https://goodfish.org.au/species/murray-cod/|access-date=2021-08-01|website=GoodFish}}</ref>

It has long been known that Murray cod could be translocated to impounded water. In the 1850s, landholder [[Terence Aubrey Murray]] stocked a large and beautiful [[billabong]]—Murray's Lagoon just north of [[Lake George (New South Wales)|Lake George]]—with Murray cod fished out of the [[Molonglo River]] at Murray's other property of  [[Yarralumla, Australian Capital Territory|Yarralumla]]. At some time the billabong overflowed and introduced Murray cod into the slightly brackish lake itself. They bred rapidly, and, from the 1850s to the 1890s, Lake George abounded with them.<ref>{{cite news|date=26 March 1863|title=(Leader:) The Golden Age|volume=IV|page=2|newspaper=[[The Golden Age (newspaper)|The Golden Age]]|issue=133|location=New South Wales, Australia|url=http://nla.gov.au/nla.news-article30633464|access-date=7 August 2017|via=National Library of Australia}}</ref>  Due to the lengthy [[Drought in Australia#Drought in the 20th century|Federation Drought]], by 1902, the lake dried out completely. In their search for water to survive in, the Murray cod flocked into the mouths of the few small creeks feeding the lake and died there by the thousands.<ref>{{cite news|date=23 November 1907|title=The Fisheries|page=14|newspaper=[[The Sydney Morning Herald]]|issue=21,794|location=New South Wales, Australia|url=http://nla.gov.au/nla.news-article14875819|access-date=7 August 2017|via=National Library of Australia}}</ref>

Farming Murray cod uses [[Fish meal|fishmeal]] and fish oil as food, but the species has a better ‘wild fish in to farmed fish out’ ratio than other  farmed species such as [[rainbow trout]] and [[Atlantic salmon]]. It commands a premium price compared to those species. It is increasingly farmed, in large dams holding water used for irrigation of farmland, where the presence of effluent produced by the fish is not a problem <ref name=":0" /> {{Clear}}

==References==
{{Reflist|30em}}

==External links==
{{Commons category|Maccullochella peelii}}
* {{Wikispecies-inline|Maccullochella peelii}}
* {{FishBase species alt | ID = 10311 | taxon = Maccullochella peelii peelii |year=2019}}
* {{cite EB1911|wstitle=Murray Cod| volume=19 |page=42|short=x}}
* [https://fishesofaustralia.net.au/home/species/4655#summary Murray Cod] on Fishes of Australia
* [https://www.nativefish.asn.au/home/page/Murray-Cod Murray cod] on Native Fish Australia

{{Taxonbar|from=Q23366}}
{{Authority control}}

[[Category:Maccullochella|Murray cod]]
[[Category:Fish of the Murray-Darling basin]]
[[Category:Taxa named by Thomas Mitchell (explorer)]]
[[Category:Vulnerable fauna of Australia]]
[[Category:Fish described in 1838|Murray cod]]