ENG Onchorhynchus_kisutch

Common names
in English
Coho salmon (Oncorhynchus kisutch)
Illustration: Timothy Knepp
Coho salmon. Silver salmon. Blueback. Hooknose. Sea trout.
Silversides. White salmon. Hoopid salmon.
… and in other languages Danish: Coholaks. Sølvlaks. Dutch: Cohozalm. Finnish: Hopealohi.
French: Saumon coho. Saumon argenté. German: Silberlachs.
Coho-Lachs. Chumlachs. Kisutch-Lachs. Icelandic: Kóhó lax.
Italian: Salmone argentato. Japanese: Gin sake. Latvian: Kižučs.
Norwegian: Coholaks. Polish: Kizucz. Portuguese: Salmao prateado.
Russian: Belaya. Belaya ryba. Kizhuch. Spanish: Salmón coho. Salmón
plateado. Swedish: Silverlax. Coholax.
Scientific name Oncorhynchus kisutch.
Also known as (synonyms): Salmo kisatch, Salmo milktschutsc,
Salmo sanguinolentus, Salmo tsuppitch and Salmo kennerlyi.
Organism group Ray-finned fishes (Actinopterygii). Salmons (Salmoniformes).
Salmonids (Salmonidae).
Size and appearance An adult coho salmon grows to a length of at least 55–75 cm, and can
reach anything up to about 90 cm (according to FishBase, 108 cm),
with a weight ranging from around 3.5 kg to as much as 14–15 kg.
The body is elongate and fusiform (spindle-shaped). At spawning time,
the males become somewhat humpbacked. In its “bright” phase (in
the sea), the species has a dark steel-blue to green head and back,
brilliant silver-coloured sides and a white underside. Females are paler
in colour than males. Both sexes have small black spots on their back,
upper sides, and dorsal and caudal fins. During spawning in fresh
waters, males turn a more distinct green on the head and back, dark
grey or black on the belly, and a characteristic bright red on the sides.
They also develop a distinctly hooked upper jaw with sharp teeth.
Females, too, change colour during spawning and develop a hooked
jaw, though it is less pronounced than in the males.
May be confused with Other salmon species in their “bright”, marine phase.
Geographical origin Northern Pacific and rivers flowing into it, from northern Japan,
Sakhalin Island and the Kamchatka Peninsula, via Alaska, British
Columbia, Washington and Oregon to California.

First observed in
Swedish waters
Occurrence in Swedish
seas and coastal areas
Occurrence in
other sea areas
Probable means
of introduction
Habitat(s) in which
species occurs
In 1984, off southern Gotland.
The only record of the species is from 1984, when a coho salmon was
caught in salmon nets off southern Gotland – possibly a stray from
stocking carried out in the then Soviet Union. (The species may not be
released into Swedish waters without a special permit.)
The species came to Europe in the 1970s, when it was deliberately
introduced into France. It found its way into the wild in 1974, when
50,000 yearlings escaped from a fish farm into the river Varenne in
Normandy. Between 1975 and 1979 similar incidents occurred in other
parts of France. Adult fish were caught between 1975 and 1977 in
various rivers of northern France and in the English Channel. Finds of
coho salmon have also been reported from Belgium and the
Netherlands.
In addition, the species has been introduced to the Great Lakes of the
United States and Canada, and to Argentina and Chile. According to
FishBase, coho salmon also occurs as an introduced species in the
Mediterranean (Israel, Cyprus, Greece and Italy).
There are reports of the species being stocked in the eastern Baltic in
the 1970s. It was observed in German waters in 1974 and in Latvian
waters in 1980. Finds have also been reported from Estonia.
Aquaculture and recreational fisheries (stocking).
Like other salmon species, coho salmon are anadromous, i.e. they live
in the sea but, after 1–2 years there, migrate into rivers (fresh waters)
in the autumn and winter to spawn. At that point, the fish are
generally 3–5 years old. Juveniles usually develop for a year or more
in rivers before descending to the sea. In the sea, coho salmon can be
found at various depths, from near the surface down to about 250 m.
This is a coldwater species, doing best at water temperatures of
around 12–14°C, which is close to its optimum temperature for
growth. When young fish were exposed to temperatures above 25°C
they died.
In a freshwater environment, young coho salmon feed mainly on
insects, while in inshore waters their diet consists of small fish, such as
herring (Clupea harengus), and crustaceans. In the open sea, adults
live on larger fish. When they ascend rivers to spawn, coho salmon
stop feeding, and after spawning the parents die.
Some populations of coho salmon in British Columbia spend their
entire lives in fresh waters.
Ecological effects Non-native salmonids may compete with other species for food and
space, and bring with them parasites and diseases that could affect
native species. Discussion about the impacts of such introductions,
however, has mostly focused on the risk of genetic effects as a threat
to indigenous salmonid species. Stocking of salmonids is practised on a
large scale and, what is more, hatchery-reared fish quite often escape
into the wild.
In this context, “genetic effects” means changes in the genetic makeup
of native species that can result from the incorporation of genes
from the new organisms. The risks associated with introducing nonnative
populations or genes into the natural environment come under
three main headings: extinction, hybridization, and loss of genetic

variation.
When closely related species or distinct populations of a single species
interbreed, hybridization can result. This can happen if individuals of a
non-native species mate with individuals of a native one. The offspring
exhibit characteristics differing, to a greater or lesser degree, from
those of the native parent. In the long term, this may result in wild
populations of a species losing some of their ability to adapt to their
environment. Stocked fish, for example, are less well adapted to their
new environment than the wild fish with which they mix.
At worst, the introduction and spread of non-native populations or
genes may drive native species to extinction. This may happen either
because the native species is outcompeted and displaced, or because
of genetic changes in the offspring (hybrid) of the alien and native
species which mean that the offspring is unable to survive. If the
hybrid is fertile, however, the next step may be an exchange of genes
with the parent population. Non-native genetic material will then be
incorporated into the native species, and in the long run the effect of
this could be to eliminate local variants.
Non-indigenous salmonid species that are stocked in Swedish waters,
then, may form hybrids with native species. Often these hybrids are
fertile, which means that they are able to reproduce in the wild. This is
true, for example, of “sparctic char” (also known as “sparctic trout” or
“spar”, a cross between brook trout Salvelinus fontinalis and Arctic
char S. alpinus), “larctic char” (lake trout Salvelinus namaycush and
Arctic char), and “splake” (male brook trout and female lake trout).
Mixing of non-native species or genetic variants with local populations
may have implications for Sweden’s populations of Arctic char, Atlantic
salmon (Salmo salar) and brown trout (Salmo trutta). Over time,
native salmonid stocks have adapted to conditions in their particular
lakes and rivers, gradually becoming genetically distinct from every
other stock of the same species. The loss of such local adaptations
may leave a population less well equipped to survive.
Stocking of hatchery-reared fish can also lead to inbreeding
depresssion. This occurs when closely related individuals mate with
one another, and may result in offspring that are unviable or have
difficulty surviving.
FIND OUT MORE
• North European and Baltic Network on Invasive Alien Species: Oncorhynchus kisutch
http://www.nobanis.org/speciesInfo.asp?taxaID=1623
• Baltic Sea Alien Species Database: Oncorhynchus kisutch
http://www.ku.lt/nemo/directory_details.php?sp_name=Oncorhynchus+kisutch
• FishBase: Oncorhynchus kisutch
http://www.fishbase.org/summary/SpeciesSummary.php?id=245&lang=English
• FAO: Fisheries Global Information System (FIGIS): Oncorhynchus kisutch
http://www.fao.org/figis/servlet/species?fid=2118
• European Nature Information System Database (EUNIS): Oncorhynchus kisutch
http://eunis.eea.europa.eu/species-factsheet.jsp?idSpecies=9980&idSpeciesLink=9980
http://www.ittiofauna.org/webmuseum/pesciossei/salmoniformes/salmonidae/salmonidae.htm
• Alaska Department of Fish & Game: Coho salmon
http://www.adfg.state.ak.us/pubs/notebook/fish/coho.php
• Environment Canada: Do you know Coho salmon?
http://www.pac.dfo-mpo.gc.ca/species/salmon/salmon_facts/coho_e.htm
• University of Toronto: Coho salmon
http://www.zoo.utoronto.ca/manuesteve/UTCoho.html

• University of British Colombia: Coho salmon
http://www.zoology.ubc.ca/~keeley/coho.htm
• Canadian Sportsfishing: Coho salmon
http://www.canadian-sportfishing.com/Tips&Techniques/Species_Info/Default1.asp?Species_Name=COHO SALMON
• Ontario Federation of Anglers and Hunters: Ontario's fish: Coho salmon
http://www.ofah.org/fishing/description.cfm?Species=Cold_Water&FishID=21
• Washington Department of Fish and Wildlife: Salmon factsUS Geological Survey:
Nonindigenous Aquatic Species: Oncorhynchus kisutch
http://nas.er.usgs.gov/queries/FactSheet.asp?speciesID=908
• NOAA: Coho salmon
http://www.glerl.noaa.gov/pubs/photogallery/Fish/pages/1071.html
• Mt. Baker-Snoqualmie National Forest Pacific Northwest Fisheries Program: Coho
http://www.fs.fed.us/r6/fishing/forests/fishresources/mtbsno_salmon.html#coho
• National Wildlife Foundation: Coho salmon
http://www.enature.com/fieldguides/detail.asp?shapeID=994&curGroupID=3&lgfromWhere=&curPageNum=8
• Wisconsin Sea Grant: Coho salmon
http://www.seagrant.wisc.edu/greatlakesfish/cohosalmon.html
• Trout Unlimited: Coho salmon
http://www.tucalifornia.org/coho.htm
• NatureServe Explorer: Oncorhynchus kisutch
http://www.natureserve.org/explorer/servlet/NatureServe?searchName=Oncorhynchus kisutch
• Trouts and Seasons of The Mountain Village: Oncorhynchus kisutch
http://www.amago.jp.lv/trout/trout42.html
IMAGES CREDIT
Illustration: Timothy Knepp. Published by U. S. Fish & Wildlife Services, Digital Library System
http://images.fws.gov/
• This factsheet on Oncorhynchus kisutch was created on 30 November 2006
• First update: 15 January 2007
• Translated by Martin Naylor on 22 January 2007