rainbow trout (Oncorhynchus mykiss) is a
species of salmonid native to tributaries
of the Pacific
Ocean in Asia and North America as well as much of the central,
western, eastern, and especially the northern portions of the
The ocean going (anadromous) form (including
those returning for spawning) are known as
, or ocean trout
(Australia and United States). The species has been introduced for food or
sport to at least 45 countries, and every continent except Antarctica.
In some of these locations, such as
, they have had very serious negative impacts on
native fish species, either by eating them, outcompeting them,
transmitting contagious diseases, or hybridization with closely
related species and subspecies that are native to western North America
The species was originally named by Johann Julius Walbaum
in 1792 based on
type specimens from Kamchatka. Richardson named a specimen of this
species Salmo gairdneri
in 1836, and in 1855, W. P.
Gibbons found a population and named it Salmo iridia
later corrected to Salmo irideus
, however these names
became deprecated once it was determined that Walbaum's type
description was conspecific and therefore had precedence (see e.g.
Behnke, 1966). More recently, DNA studies showed rainbow trout are
genetically closer to Pacific salmon (Onchorhynchus
species) than to brown trout
) or Atlantic Salmon
the genus was changed.
Unlike the species' former name's epithet iridia
( ), the
from the local Kamchatkan name 'mykizha'; all of Walbaum's species
names were based on Kamchatkan local names.
Illustration of a rainbow trout
, steelhead are anadromous
: they return to their original
hatching ground to spawn. Steelhead rejuvenate after spawning, so
they may return to the oceans to start the anadromous cycle once
again. The steelhead smolts (immature or young fish) usually remain
in the river for about a year before heading to sea, whereas salmon
typically return to the seas as smolts. Different populations of
different times of the year. "Summer-run steelhead" migrate between
May and October, before their reproductive organs are fully mature.
They mature in freshwater before spawning in the spring.
"Winter-run steelhead" mature fully in the ocean before migrating,
between November and April, and spawn shortly after returning.
Similar to Atlantic salmon, but unlike their Pacific
kin, steelhead are iteroparous
and may make several spawning trips
between fresh and salt water. The maximum recorded life-span for a
rainbow trout is 11 years. Salmon is often sold as a replacement
because they taste similar.
Rainbow trout are predators with a varied diet, and will eat nearly
anything they can grab, in contrast to the legendary, selective
image people often have of the fish's dietary habits. Rainbows are
not quite as piscivorous or aggressive as the brown trout
. When young, insects make up a large portion of the
diet, as well as fish eggs, smaller fish (up to 1/3 of their
length), along with crayfish and other crustaceans make up the
remainder. As they grow, though, the proportion of fish increases
in most all populations. Some lake dwelling lines may become
planktonic feeders. While in flowing waters populated with salmon,
trout will eat varied fish eggs, to include salmon, cutthroat
trout, as well as the eggs of other rainbow trout, alvein, fry,
smolt and even salmon carcasses.
Length and Weight
As rainbow trout grow longer, they
increase in weight. The relationship between length and weight is
not linear. The relationship between total length (L, in inches)
and total weight (W, in pounds) for nearly all species of fish can
be expressed by an equation of the form:
- W = cL^b\!\,
Invariably, b is close to 3.0 for all species, and c is a constant
that varies among species. For lentic rainbow trout, b = 2.990 and
c = 0.000426, and for lotic rainbow trout, b = 3.024 and c =
The relationship described in this section suggests that a 13-inch
lentic rainbow trout will weigh about 1.0 pound, while an 18-inch
lentic rainbow trout will weigh about 2.5 pounds.
Rainbow trout and steelhead are both highly desired food and
sportfish. A number of angling methods are commonly employed.
Rainbow trout are a popular target for fly fishers. Spinners,
spoons, and small crankbaits can also be used productively, either
casting or trolling. Rainbow trout can also be caught on live bait;
nightcrawlers, trout worms, and minnows are popular and effective
They are farmed
in many countries
throughout the world. Since the 1950s commercial production has
grown exponentially, particularly in Europe and recently in Chile.
Worldwide, in 2007, 604,695 tonnes of farmed salmon trout were
harvested with a value of 2.589 billion USD dollars. The largest
producer is Chile. In Chile and Norway, the ocean cage production
of steelhead has expanded to supply export markets. Inland
production of rainbow trout to supply domestic markets has
increased strongly in countries such as Italy, France, Germany,
Denmark and Spain. Other significant producing countries include
the USA, Iran, Germany and the UK.
There are tribal commercial fisheries for steelhead in the Puget
Sound, the Washington Coast and in the Columbia River.
Threats and conservation
Steelhead trout have declined due to a number of human and natural
causes. The U.S. National Marine Fisheries
has a detailed description of threats
. Steelhead that spawn
in Southern California streams
(south of Point
Conception) have been
affected by habitat loss due to dams, confinement of streams in
concrete channels, water pollution, groundwater pumping, urban heat island effects, and other
byproducts of urbanization.
The U.S. National Marine Fisheries
Service has identified 15 populations, called Distinct
Population Segments(DPSs), of steelhead trout in Washington, Oregon and
Eleven of these DPSs are listed under the U.S.
Endangered Species Act
One DPS on the Oregon Coast is designated a U.S. Species of Concern
. Species of Concern are those
species about which the National Marine Fisheries Service has some
concerns regarding status and threats, but for which insufficient
information is available to indicate a need to list the species
under the ESA.
The rainbow trout is susceptible to enteric redmouth disease
. There has
been considerable research conducted on redmouth disease, as its
implications for rainbow trout farmers are significant. The disease
does not affect humans.
Rainbow trout, and subspecies thereof, are currently EPA approved
indicator species for acute fresh water aquatic toxicity
File:Lake Washington Ship Canal Fish Ladder pamphlet - ocean phase
Steelhead.jpg|Male ocean phase steelheadFile:Lake Washington Ship
Canal Fish Ladder pamphlet - male freshwater phase
Steelhead.jpg|Male spawning phase steelheadFile:Jumping
Salmon.jpg|Steelhead attempting to jump some
rapidsImage:SteelheadRainbowTrout.jpg|Steelhead with clear spot
pattern on fins and body
Rainbow trout and steelhead are popular in Western cuisine and are
both caught wild
for food. It has tender flesh and a mild,
somewhat nutty flavor. However, farmed trout and those taken from
certain lakes have a pronounced earthy flavor which many people
find unappealing; many shoppers therefore make it a point to
ascertain the source of the fish before buying. Rainbow trout are
raised in many countries throughout the world. Rainbow trout that
are wild have a diet of scuds (freshwater shrimp), insects such as
flies, and crayfish
are the most appealing.
Dark red/orange meat indicates that it is either an anadromous
steelhead or a farmed Rainbow trout given a supplemental diet with
a high astaxanthin
resulting pink flesh is marketed under monikers like Ruby Red or
Steelhead meat is pink like that of salmon, and is more flavorful
than the light-colored meat of rainbow trout.
The sperm of rainbow trout contains protamine
as does that of salmon and some other
species of similar fish. Protamine sulphate is an "antidote" to the
. Originally protamine
was isolated from fish sperm, but is now produced in the
laboratory. Back when the pilgrims came to America native Americans
used the skin of the rainbow trout as medicine.
A few populations are recognized as subspecies:
- Kamchatkan rainbow
mykiss mykiss (Walbaum, 1792).
- Columbia River redband
trout, Oncorhynchus mykiss gairdnerii (Richardson, 1836).
- Coastal rainbow trout,
irideus (Gibbons, 1855).
trout, isolated in Lake Crescent (Washington), Oncorhynchus mykiss irideus var.
beardsleei (not a true subspecies, but a lake dwelling variety
of Coastal rainbow trout) (Jordan,
- Great Basin redband
trout, Oncorhynchus mykiss newberrii (Girard,
- Golden trout, Oncorhynchus
mykiss aguabonita (Jordan, 1892).
- Kamloops rainbow trout,
kamloops (Jordan, 1892).
- Kern River rainbow
trout, Oncorhynchus aguabonita
gilberti (Jordan, 1894).
- Sacramento golden trout,
aguabonita stonei (Jordan, 1894).
- Little Kern golden
trout, Oncorhynchus aguabonita
whitei (Evermann, 1906).
- Baja California
rainbow trout, Nelson's trout, or San Pedro Martir trout,
nelsoni (Evermann, 1908).
- Eagle Lake rainbow
trout, Oncorhynchus mykiss
aquilarum (Snyder, 1917).
- McCloud River redband,
- Sheepheaven Creek
Golden rainbow trout are bred from a single mutated color variant
of Oncorhynchus mykiss
. Golden rainbow trout are
predominantly yellowish, lacking the typical green field and black
spots, but retaining the diffuse red stripe. The palomino trout is
a mix of golden and common rainbow trout, resulting in an
intermediate color. The golden rainbow trout should not be confused
with the naturally occurring golden
- Scott and Crossman (1985) Freshwater Fishes of Canada.
Bulletin 184. Fisheries Research Board of Canada. Page 189. ISBN