Editing Cod (section)

==Ecology==
{{See also|Diseases and parasites in cod}}
[[File:Lernaeocera branchialis.jpg|thumb|right|A fish with its gills infested with two [[cod worm]]s]]
Adult cod are active hunters, feeding on [[sand eel]]s, [[merlangius merlangus|whiting]], [[haddock]], small cod, [[squid]], [[crab]]s, [[lobster]]s, [[mussel]]s, [[worm]]s, [[mackerel]], and [[mollusc]]s.

In the Baltic Sea the most important prey species are [[Atlantic herring|herring]] and [[Sprattus sprattus|sprat]].<ref name=Koster2001/> Many studies that analyze the stomach contents of these fish indicate that cod is the top predator, preying on the herring and sprat.<ref name=Koster2001>{{cite journal|title=Developing Baltic cod recruitment models. I. Resolving spatial and temporal dynamics of spawning stock and recruitment for cod, herring, and sprat|journal=Canadian Journal of Fisheries and Aquatic Sciences|volume=58|issue=8|year=2001|pages=1516–1533|url=http://bioweb.coas.oregonstate.edu/~ciannellilab/cameo/articles/neuenfeldt/2001k%F6steretal.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://bioweb.coas.oregonstate.edu/~ciannellilab/cameo/articles/neuenfeldt/2001k%F6steretal.pdf |archive-date=2022-10-09 |url-status=live|doi=10.1139/cjfas-58-8-1516|last1=Köster|first1=Friedrich W.|last2=Möllmann|first2=Christian|last3=Neuenfeldt|first3=Stefan|last4=St John|first4=Michael A|last5=Plikshs|first5=Maris|last6=Voss|first6=Rüdiger}} {{dead link|date=August 2017 |bot=InternetArchiveBot |fix-attempted=yes }}</ref> Sprat form particularly high concentrations in the [[Bornholm]] Basin in the southern Baltic Sea.<ref name=Casini2004>{{cite journal|author1=Casini, Michele |author2=Cardinale, Massimiliano |author3= Arrheni, Fredrik |name-list-style=amp |title=Feeding preferences of herring (''Clupea harengus'') and sprat (''Sprattus sprattus'') in the southern Baltic Sea|doi=10.1016/j.icesjms.2003.12.011|year=2004|journal=ICES Journal of Marine Science|volume=61|issue=8|page=1267|bibcode=2004ICJMS..61.1267C |doi-access=free}}</ref> Although cod feed primarily on adult sprat, sprat tend to prey on the cod eggs and larvae.<ref name=Nissling2004>{{cite journal|author=Nissling, Anders|title=Effects of temperature on egg and larval survival of cod (''Gadus morhua'') and sprat (''Sprattus sprattus'') in the Baltic Sea – implications for stock development|doi=10.1023/B:hydr.0000018212.88053.aa|year=2004|journal=Hydrobiologia|volume=514|issue=1–3|pages=115–123|bibcode=2004HyBio.514..115N |s2cid=59944278}}</ref>

Cod and related species are plagued by parasites. For example, the [[cod worm]], ''Lernaeocera branchialis'', starts life as a [[copepod]]-like larva, a small free-swimming crustacean. The first host used by the larva is a [[flatfish]] or [[lumpsucker]], which it captures with grasping hooks at the front of its body. It penetrates the fish with a thin [[wiktionary:filament|filament]], which it uses to suck the fish's blood. The nourished larvae then mate on the fish.<ref name="Matthews">{{cite book|first=Bernard E. |last=Matthews|title=An Introduction to Parasitology |url={{google books |plainurl=y |id=UILMlQpNVCYC}}|date=1998 |publisher=Cambridge University Press |isbn=978-0-521-57691-8 |pages=73–74}}</ref><ref name="Piper">{{cite book
|year=2007
|title=Extraordinary Animals: An Encyclopedia of Curious and Unusual Animals
|url=https://archive.org/details/extraordinaryani0000pipe|url-access=registration|publisher=[[Greenwood Press (publisher)|Greenwood Press]]|isbn=9780313339226
}}</ref> The female larva, with her now fertilized eggs, then finds a cod, or a cod-like fish such as a [[haddock]] or [[Whiting (fish)|whiting]]. There the larva clings to the [[gill]]s while it metamorphoses into a plump sinusoidal wormlike body with a coiled mass of egg strings at the rear. The front part of the worm's body penetrates the body of the cod until it enters the rear bulb of the host's [[heart]]. There, firmly rooted in the cod's circulatory system, the front part of the parasite develops like the branches of a tree, reaching into the main [[artery]]. In this way, the worm extracts nutrients from the cod's blood, remaining safely tucked beneath the cod's gill cover until it releases a new generation of offspring into the water.<ref name="Matthews" /><ref name="Piper" />

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