Salmonidae

Salmonidae; Temporal range:Early Eoceneto present PreꞒ Ꞓ O S D C P T J K Pg N
	Chinook salmon(Oncorhynchus tschawytscha)
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Actinopterygii
Superorder:	Protacanthopterygii
Order:	Salmoniformes; Bleeker,1859
Family:	Salmonidae; G. Cuvier,1816
Type species
	Salmo salar; Linnaeus,1758
Genera
	(see text)

Salmonidae(/sælˈmɒnɪdiː/,lit. "salmon-like" ) is afamilyofray-finned fishthat constitutes the only currentlyextantfamily in theorderSalmoniformes(/sælˈmɒnɪfɔːrmiːz/,lit. "salmon-shaped" ), consisting of 11 extantgeneraand over 200speciescollectively known as "salmonids"or"salmonoids".The family includessalmon(both Atlantic and Pacific species),trout(both ocean-going and landlocked),char,graylings,freshwater whitefishes,taimensandlenoks,allcoldwatermid-level predatory fishthat inhabit thesubarcticand cooltemperatewaters of theNorthern Hemisphere.TheAtlantic salmon(Salmo salar), whoseLatinname became that of itsgenusSalmo,is also theeponymof the family and order names.

Salmonids have a relatively primitive appearance amongteleostfish, with thepelvic finsbeing placed far back, and anadipose fintowards the rear of the back. They have slender bodies with roundedscalesand forkedtail fins,and theirmouthscontain a single row of sharpteeth.^[2]Although the smallest salmonid species is just 13 cm (5.1 in) long for adults, most salmonids are much larger, with the largest reaching 2 m (6 ft 7 in).^[3]

All salmonids aremigratory fishthatspawnin the shallowgravel bedsoffreshwater headstreams,spend the growingjuvenileyears inrivers,creeks,smalllakesandwetlands,but migrate downstream upon maturity and spend most of theiradultlives at much larger waterbodies. Many salmonid species areeuryhalineand migrate to theseaorbrackish estuariesas soon as they approach adulthood, returning to the upper streams only to reproduce. Such sea-run life cycle is described asanadromous,and other freshwater salmonids that migrate purely between lakes and rivers are consideredpotamodromous.Salmonids arecarnivorous predatorsof the middlefood chain,feeding on smaller fish,crustaceans,aquatic insectsandlarvae,tadpolesand sometimesfish eggs(even those of their own kind),^[2]and in turn being preyed upon by larger predators. Many species of salmonids are thus consideredkeystone organismsimportant for bothfreshwaterandterrestrial ecosystemsdue to thebiomasstransfer provided by their mass migration from oceanic to inland waterbodies.

Evolution

Eosalmo driftwoodensisfossil
Klondike Mountain Formation

Current salmonids comprise three maincladestaxonomically treated assubfamilies:Coregoninae(freshwater whitefishes),Thymallinae(graylings), andSalmoninae(trout,salmon,char,taimensandlenoks). Generally, all threelineagesare accepted to allocate a suite of derived traits indicating amonophyleticgroup.^[1]

The order Salmoniformes first appeared during theSantonianandCampanianstages of theLate Cretaceous,^[4]^[5]and is most closely related topikeandmudminnowsin the orderEsociformes,to the extent that some authors have grouped the Esociformes within the Salmoniformes.^[6]Although it is assumed that salmon and pike diverged from one another during the Cretaceous, no definitive salmonids appear before theEocene.^[7]The Salmonidae first appear in thefossilrecord in theEarly Eocene^[8]withEosalmo driftwoodensis,a stem-salmonine,which was first described from fossils found atDriftwood Creek,centralBritish Columbia,^[7]and has been recovered from most sites in theEocene Okanagan Highlands.^[9]^[10]^[11]This genus shares traits found in all three subfamily lineages. Hence,E. driftwoodensisis an archaic salmonid, representing an important stage in salmonid evolution.^[1]Fossil scales ofcoregoninesare known from the Late Eocene or Early Oligocene of California.^[12]

A gap appears in the salmonine fossil record afterE. driftwoodensisuntil about 7 million years ago (mya), in theLate Miocene,when trout-like fossils appear inIdaho,in theClarkia Lake beds.^[13]Several of these species appear to beOncorhynchus— the current genus for Pacific salmon and Pacific trout. The presence of these species so far inland established thatOncorhynchuswas not only present in the Pacific drainages before the beginning of thePliocene(~5–6 mya), but also thatrainbowandcutthroat trout,and Pacific salmon lineages had diverged before the beginning of the Pliocene. Consequently, the split betweenOncorhynchusandSalmo(Atlantic salmon and European trout) must have occurred well before the Pliocene. Suggestions have gone back as far as theEarly Miocene(about 20 mya).^[1]^[14]

Genetics

Oncorhynchus mykissmaturing from eggs.

Based on the most current evidence, salmonids diverged from the rest ofteleost fishno later than 88 million years ago, during the lateCretaceous.This divergence was marked by awhole-genome duplication eventin the ancestral salmonid, where the diploid ancestor becametetraploid.^[15]^[16]This duplication is the fourth of its kind to happen in the evolutionary lineage of the salmonids, with two having occurred commonly to all bony vertebrates, and another specifically in the teleost fishes.^[16]

Extant salmonids all show evidence of partial tetraploidy, as studies show the genome has undergone selection to regain a diploid state. Work done in therainbow trout(Onchorhynchus mykiss) has shown that the genome is still partially-tetraploid. Around half of the duplicated protein-coding genes have been deleted, but all apparentmiRNA sequencesstill show full duplication, with potential to influence regulation of the rainbow trout's genome. This pattern of partial tetraploidy is thought to be reflected in the rest of extant salmonids.^[17]

The first fossil species representing a true salmonid fish (E. driftwoodensis) does not appear until the middle Eocene.^[18]This fossil already displays traits associated with extant salmonids, but as the genome of E.driftwoodensiscannot be sequenced, it cannot be confirmed if polyploidy was present in this animal at this point in time. This fossil is also significantly younger than the proposed salmonid divergence from the rest of the teleost fishes, and is the earliest confirmed salmonid currently known. This means that the salmonids have a ghost lineage of approximately 33 million years.

Given a lack of earlier transition fossils, and the inability to extract genomic data from specimens other than extant species, the dating of the whole-genome duplication event in salmonids was historically a very broad categorization of times, ranging from 25 to 100 million years in age.^[17]New advances incalibrated relaxed molecular clock analyseshave allowed for a closer examination of the salmonid genome, and has allowed for a more precise dating of the whole-genome duplication of the group, that places the latest possible date for the event at 88 million years ago.^[16]

This more precise dating and examination of the salmonid whole-genome duplication event has allowed more speculation on the radiation of species within the group. Historically, the whole-genome duplication event was thought to be the reason for the variation within Salmonidae. Current evidence done with molecular clock analyses revealed that much of the speciation of the group occurred during periods of intense climate change associated with the last ice ages, with especially high speciation rates being observed in salmonids that developed an anadromous lifestyle.^[16]

Classification

Together with the closely related ordersEsociformes(pikesandmudminnows),Osmeriformes(true smelts) andArgentiniformes(marine smeltsandbarreleyes), Salmoniformes comprise thesuperorder Protacanthopterygii.

The only extant family within Salmoniformes, Salmonidae, is divided into threesubfamiliesand around 10generacontaining about 220species.The concepts of the number of species recognised vary among researchers and authorities; the numbers presented below represent the higher estimates of diversity:^[3]

Phylogeny of Salmonidae^[19]^[20]

Coregoninae

Prosopium

	Stenodus

	Coregonus

Thymallinae

Thymallus

Salmoninae

	Salmo

	Salvelinus(incl.Salvethymus)

Oncorhynchus

Brachymystax

	Parahucho

	Hucho

OrderSalmoniformes

Family:Salmonidae
- Subfamily:Coregoninae
  - Coregonus- whitefishes (78 species)
  - Prosopium- round whitefishes (6 species)
  - Stenodus-beloribitsaandnelma(1 or 2 species)
  - †Beckius(1 species, Oligocene)^[12]
  - †Parastenodus(1 species, Eocene)^[12]
- Subfamily:Thymallinae
  - Thymallus- graylings (14 species)
- Subfamily: Salmoninae
  - †Eosalmo(1 species,Eocene)
  - Tribe:Salmonini
    - Salmo-Atlantic salmonandtrout(47 species)
    - Salvelinus- Char and trout (e.g.brook trout,lake trout) (51 species)
    - Salvethymus-Long-finned char(1 species)
  - Tribe: Oncorhynchini
    - Brachymystax-lenoks(4 species)
    - Hucho-taimens(4 species)
    - Oncorhynchus- Pacific salmon and trout (12 species)
    - Parahucho-Sakhalin taimen(1 species)

Hybrid crossbreeding

The following table shows results of hybrid crossbreeding combination in Salmonidae.^[21]

Crossbreeding
			male
			Salvelinus		Oncorhynchus								Salmo
			leucomaenis (white-spotted char)	fontinalis (Brook trout)	mykiss (Rainbow trout)	masou masou (masu salmon)	masou ishikawae (Amago Salmon)	gorbuscha (pink salmon)	nerka (Sockeye salmon)	keta (chum salmon)	kisutsh (coho salmon)	tshawytscha (chinook salmon)	trutta (Brown trout)	salar (Atlantic Salmon)
female
	(Salvelinus)	leucomaenis (white-spotted char)	-	O	X	O	O		X	X			O
	(Salvelinus)	fontinalis (Brook trout)	O	-	X	O	O		X	X	O		X	X
	(Oncorhynchus)	mykiss (Rainbow trout)	O	O	-	O	O	O	X	X	X		X	X
		masou masou (masu salmon)	O	X	X	-	O		X	X	O	O	X
		masou ishikawae (Amago Salmon)	O	O	X	O	-		X				O
		gorbuscha (pink salmon)	X					-	O	O		O
		nerka (Sockeye salmon)	X	X	X	X	X	O	-	O	O	O	X
		keta (chum salmon)	X	X	X	X		O	O	-	O	X		X
		kisutsh (coho salmon)		X	X			O	O	X	-	O	X	X
		tshawytscha (chinook salmon)				O		O	O	X	O	-
	Salmo	trutta (Brown trout)	O	O	X	O	O		X		X		-	O
	Salmo	salar (Atlantic Salmon)		O	X					X	X		O	-

note:-: The identical kind, O: (survivability), X: (Fatality)

References

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^^a ^bMcDowell, Robert M. (1998). Paxton, J.R.; Eschmeyer, W.N. (eds.).Encyclopedia of Fishes.San Diego:Academic Press.pp. 114–116.ISBN 978-0-12-547665-2.
^^a ^bFroese, Rainer;Pauly, Daniel (eds.)."Family Salmonidae".FishBase.December 2008 version.
^Szabó, Márton; Ősi, Attila (September 2017)."The continental fish fauna of the Late Cretaceous (Santonian) Iharkút locality (Bakony Mountains, Hungary)".Central European Geology.60(2): 230–287.Bibcode:2017CEJGl..60..230S.doi:10.1556/24.60.2017.009.hdl:10831/67493.ISSN 1788-2281.
^Brinkman, Donald B.; Newbrey, Michael G.; Neuman, Andrew G.; Eaton, Jeffrey G. (2013)."Freshwater Osteichthyes from the Cenomanian to Late Campanian of Grand Staircase–Escalante National Monument, Utah".In Titus, Alan L.; Loewen, Mark A. (eds.).At the Top of the Grand Staircase: The Late Cretaceous of Southern Utah.Bloomington: Indiana University Press. pp. 195–236.ISBN 9780253008961.
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^Wilson, M.V.H.; Li, Guo-Qing (1999)."Osteology and systematic position of the Eocene salmonid †Eosalmo driftwoodensisWilson from western North America "(PDF).Zoological Journal of the Linnean Society.99(125): 279–311.doi:10.1111/j.1096-3642.1999.tb00594.x.Retrieved2010-01-01.
^Wilson, M.V.H. 2009. McAbee Fossil Site Assessment Report. 60 pp.Online PDF.Accessed 17 May 2021.
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^Smiley, Charles J."Late Cenozoic History of the Pacific Northwest"(PDF).Association for the Advancement of Science: Pacific Division. Archived fromthe original(PDF)on August 4, 2004.RetrievedAugust 8,2006.
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^Allendorf, Fred W.; Thorgaard, Gary H. (1984). "Tetraploidy and the Evolution of Salmonid Fishes".Evolutionary Genetics of Fishes.pp. 1–53.doi:10.1007/978-1-4684-4652-4_1.ISBN 978-1-4684-4654-8.
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^Crête-Lafrenière, Alexis; Weir, Laura K.; Bernatchez, Louis (2012)."Framing the Salmonidae Family Phylogenetic Portrait: A More Complete Picture from Increased Taxon Sampling".PLOS ONE.7(10): e46662.Bibcode:2012PLoSO...746662C.doi:10.1371/journal.pone.0046662.PMC3465342.PMID 23071608.
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^Ito, Daisuke; Fujiwara, Atushi; Abe, Syuiti (2006)."Hybrid Inviability and Chromosome Abnormality in Salmonid Fish".The Journal of Animal Genetics.34:65–70.doi:10.5924/abgri2000.34.65.