Lernaeocera branchialis

{{Short description|Species of crustacean}} {{Speciesbox | image = Lernaeocera branchialis.jpg | image_alt = | image_caption = The gills of a whiting infested by two blood-sucking ''Lernaeocera branchialis'' | status = | status_system = | status_ref = {{citation needed|date=}} | genus = Lernaeocera | species = branchialis | authority = (Linnaeus, 1767) | synonyms = * ''Lernaea branchialis'' Linnaeus, 1767 * ''Lernaea gobina'' O. F. Müller, 1776 * ''Lernaea lumpi'' T. Scott, 1901 * ''Lernaeocera lumpi'' (T. Scott, 1901) * ''Lernaeocera megacephala'' A. Scott, 1929 * ''Lernaeocera obtusa'' Kabata, 1957 * ''Lernaeocera wilsoni'' J. H. Schuurmans Stekhoven Jr., 1936 | synonyms_ref = <ref>{{cite web |author=Geoff Boxshall |year=2011 |title=''Lernaeocera branchialis'' (Linnaeus, 1767) |editor=T. Chad Walter & Geoff Boxshall |work=World Copepoda database |publisher=World Register of Marine Species |url=http://www.marinespecies.org/aphia.php?p=taxdetails&id=135993 |accessdate=March 11, 2011}}</ref> }}

'''''Lernaeocera branchialis''''', sometimes called '''cod worm''', is a parasite of marine fish, found mainly in the North Atlantic.<ref>{{cite journal |author=J. B. Jones |year=1998 |title=Distant water sailors: parasitic Copepoda of the open ocean |journal=Journal of Marine Systems |volume=15 |issue=1–4 |pages=207–214 |doi=10.1016/S0924-7963(97)00056-0|bibcode=1998JMS....15..207J }}</ref> It is a marine copepod which starts life as a small pelagic crustacean larva. It is among the largest of copepods, ranging in size from {{convert|2|to|3|mm|in|frac=32|abbr=off}} when it matures as a copepodid larva to more than {{convert|40|mm|in|frac=2|abbr=on}} as a sessile adult.

''Lernaeocera branchialis'' is ectoparasitic, which means it is a parasite that lives primarily on the surface of its hosts. It has many life stages, some of which are motile and some of which are sessile. It goes through two parasitic stages, one where it parasitizes as a secondary host a flounder or lumpsucker, and another stage where it parasitizes as a primary host a cod or other fishes of the cod family (gadoids). It negatively impacts the commercial fishing and mariculture of cod-like fish.

==Life stages== The life-cycle of a cod worm involves a complex progression of life stages, including two successive hosts. It comprises "two free-swimming nauplius stages, one infective copepodid stage, four chalimus stages and the adult copepod, each separated by a moult".<ref name="Brooker" />

The cycle begins with the females laying eggs which hatch into a nauplius, the usual early larval stage of crustaceans.<ref name="Matthews" /> This nauplius I moults about 10 minutes after hatching to produce nauplius II, and 48 hours later, nauplius II moults to a copepodid stage. At this point the copepodid is pelagic and free-swimming with an average length of about 0.5 mm.<ref name="Brooker" />

The next stage is finding a secondary or intermediate host, a demersal fish like a flounder or lumpfish which is often stationary and therefore easy to catch. The copepodid has only a day to find such a fish and attach itself to the fish's gills.<ref name="Matthews" />

When they locate such a fish, they capture it with grasping hooks at the front of their body. They penetrate the fish with a thin filament which they use to suck its blood. The nourished cod worms then progress via four moults from the naupliar stage to the mature chalimus stage. At this point the males transfer sperm to the females. Both sexes develop swimming setae, detach from the flounder or lumpfish and again swim freely as pelagic organisms.<ref name="Matthews">{{Cite book |author=Bernard E. Matthews |year=1998 |title=An Introduction to Parasitology |chapter=From host to host |pages=[https://archive.org/details/introductiontopa0000matt/page/52 52–78] |publisher=Cambridge University Press |isbn=978-0-521-57691-8 |url=https://archive.org/details/introductiontopa0000matt/page/52 }}</ref><ref name="Piper">{{cite book |author=Ross Piper |author-link=Ross Piper |year=2007 |title=Extraordinary Animals: An Encyclopedia of Curious and Unusual Animals |url=https://archive.org/details/extraordinaryani0000pipe |url-access=registration |publisher=Greenwood Press |isbn=978-0-313-33922-6 |chapter=Cod worm |pages=[https://archive.org/details/extraordinaryani0000pipe/page/180 180–182]}}</ref>

The female cod worm still resembles a copepod and is 2 to 3 mm long. Females undergo another pelagic quest, searching this time for a definitive or primary host. With her fertilised eggs, she looks for a cod or a fish belonging to the same family as cod, such as a haddock or whiting.<ref name="Matthews" />

When a suitable definite host is located, females enter the gill chamber. There, while attached to a gill, the female develops a plump, sinusoidal, worm-like body, with a coiled mass of egg strings at the posterior end.<ref name="Matthews" /> Females now measure about 20 mm long, but can grow up to 50 mm.<ref>{{cite book |author=Z. Kabata |year=1979 |title=Parasitic Copepoda of British Fishes |publisher=Ray Society |location=London |isbn=978-0-903874-05-2}}</ref> The oral end of the female copepod 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 in the shape of antlers or branches on a tree, reaching into the main artery. In this way, while safely tucked beneath the cod's gill cover, the female's deeply embedded oral end can feed on blood while eggs develop and are released into the water column from the posterior end.<ref name="Matthews" /><ref name="Piper" />

==Behaviour== It is not known how ''L. branchialis'' searches for its fish hosts, but it probably uses chemoreceptors and mechanoreceptors, and follows physical clues in the water column such as those provided by haloclines and thermoclines.<ref name="Brooker">{{cite thesis |author=Adam Jonathan Brooker |year=2007 |url=http://dspacedev.stir.ac.uk/bitstream/1893/343/1/Brooker_AJ_PhD_Thesis.pdf |title=Aspects of the biology and behaviour of ''Lernaeocera branchialis'' (Linnaeus, 1767) (Copepoda : Pennellidae) |degree=PhD |publisher=University of Stirling }}{{dead link|date=December 2017 |bot=InternetArchiveBot |fix-attempted=yes }}</ref>

==Effects on fisheries== The most serious parasitic crustaceans among fish in general are sea lice.<ref name="Scholz">{{cite journal |author=Tomáš Scholz |year=1999 |title=Parasites in cultured and feral fish |journal=Veterinary Parasitology |volume=84 |issue=3–4 |pages=317–335 |url=http://www.cnr.uidaho.edu/fish422and424/Fish%20Health%20424/424LabFiles/Lab%209%20Parasitology/Parasites%20Review.pdf |pmid=10456421 |doi=10.1016/S0304-4017(99)00039-4 |url-status=dead |archiveurl=https://web.archive.org/web/20110718075109/http://www.cnr.uidaho.edu/fish422and424/Fish%20Health%20424/424LabFiles/Lab%209%20Parasitology/Parasites%20Review.pdf |archivedate=2011-07-18 }}</ref> However, ''L. branchialis'' is probably the most serious parasitic crustacean among cod. Infestation reduces the efficiency with which food can be utilised, delaying the development of the gonads. Up to 30% loss in weight can occur, with increases in mortality because of open lesions with loss of blood, and possibly occlusion of vessels or aorta.<ref name="Scholz" /> These can have commercial impacts on wild fisheries, making cod-like fishes more expensive to market.<ref name="Scholz" /><ref>{{cite book |author=Klaus Rohde |year=1993 |title=Ecology of Marine Parasites: An Introduction to Marine Parasitology |page=198 |edition=2nd |publisher=CAB International |isbn=978-0-85198-845-0}}</ref> Gadoids, particularly cod, are emerging marine aquaculture species in some North Atlantic countries. ''L. branchialis'' present potential problems for their successful mariculture.<ref>Fisheries Research Services (2005) [http://www.scotland.gov.uk/Uploads/Documents/Final%20interactions%20report.pdf Final report of the Aquaculture Health Joint Working Group sub-group on disease risks and interactions between farmed salmonids and emerging marine aquaculture species] Page 29. Scotland. {{ISBN|0-9546490-8-7}}</ref>

== See also == * {{Portal inline|Crustaceans}}

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

==Further reading== * {{Cite journal |author=Adam J. Brooker, Andrew P. Shinn & James E. Bron |year=2007 |title=A review of the biology of the parasitic copepod ''Lernaeocera branchialis'' (L., 1767) (Copepoda: Pennellidae) |journal=Advances in Parasitology |volume=65 |pages=297–341 |doi=10.1016/S0065-308X(07)65005-2 |pmid=18063099|isbn=9780123741660 }} * {{Cite book |author=Larry S. Roberts, John Janovy & Gerald D. Schmidt |year=2009 |title=Foundations of Parasitology |edition=8th |publisher=McGraw-Hill |isbn=978-0-07-128458-5}}

Category:Parasitic animals of fish Category:Crustaceans described in 1767 Category:Copepods of the Atlantic Ocean Category:Ectoparasites Category:Parasitic crustaceans Category:Siphonostomatoida Category:Animal taxa named by Carl Linnaeus