名字：rainbow trout ,belongs to trout family.
rainbow trout
A freshwater food and game fish (Oncorhynchus mykiss) native to western North America, having a reddish longitudinal band and black spots.
rainbow trout
Species (Oncorhynchus mykiss) of fish in the salmon family (Salmonidae) noted for spectacular leaps and hard fighting when hooked. It has been introduced from western North America to many other countries. A brightly coloured fish of lakes and swift streams, it is covered with small black spots and has a reddish band along either side. The steelhead, a large, bluish, oceangoing form, is also a prized game fish. Rainbow trout may weigh 6 lb (2.8 kg); steelheads (and rainbows in large lakes) may weigh 10–20 lb (4.5–9 kg) or more. Another form of rainbow, the Kamloops, or Kootenay, trout of Idaho, may exceed 30 lb (14 kg).
Rainbow trout
Oncorhynchus mykiss
FAMILY
Salmonidae
TAXONOMY
Salmo mykiss Walbaum, 1792, mouth of Columbia River at Fort Vancouver, Washington State, United States.
OTHER COMMON NAMES
English: Rainbow trout (North American landlocked populations), steelhead (sea populations); French: Truite arc-en-ciel; German: Regenbogenforelle; Spanish: Trucha arco iris.
PHYSICAL CHARACTERISTICS
Length 47.2 in (120 cm); weight 56 lb (25.4 kg). Body elongate and somewhat compressed, especially in larger individuals. Brightly colored, varies in color (especially males) depending upon habitat, size, and sexual condition. Stream residents and spawners are darker with more intense colors, lake residents tend to be lighter, brighter, and more silvery.
DISTRIBUTION
Eastern Pacific from Alaska to Baja California, Mexico. This is one of the most widely introduced fishes in the world in at least 50 countries, which makes its present distribution virtually global. In tropical countries where it has been introduced it is found only above 4,000 ft (about 1,200 m) of altitude above sea level. Introduction has had a negative ecological impact in many parts of the world.
HABITAT
Fresh waters where the water temperature is not higher than 53.6°F (12°C) in summer. Although they can be found in cold lakes, they require moderate-to-fast flowing, well-oxygenated waters for breeding. Yet, their survivorship is better in lakes than in streams.
BEHAVIOR
Adults aggressively defend feeding territories. All stocks of rainbow trout are opportunistic regarding migration, since they are able to migrate to, or at least to adapt to sea water, according to environmental factors. This may be another case of extreme behavioral plasticity.
FEEDING ECOLOGY AND DIET
Benthic feeders. Adults consume mostly aquatic and terrestrial insects, mollusks, crustaceans, fish eggs, minnows, and other small fishes (including other trouts). Young feed mostly on zoo-plankton. Ocean-going populations are vulnerable to larger fishes, pinnipeds, and toothed whales. Freshwater populations are preyed upon by larger fishes, otters, bears, and fish-eating birds.
REPRODUCTIVE BIOLOGY
As for other salmonids, growth rate varies according to environmental conditions. Usually reach sexual maturity between two and three years of age, with some extreme cases becoming sexually mature at five years. In this species, the female finds a spot and digs a pit. However, while she digs she is accompanied by an attendant male, which courts her and also drives away other males. Once the pit is completed, the female drops into it, immediately followed by the male. When the pair is side by side, they open their mouths, quiver, and release egg and sperm. A total of 700–4,000 eggs are produced per spawning event, which are then fertilized by the subordinate male. The female then quickly moves to the upstream edge of the nest and starts digging a new pit, covering the eggs. This process goes on for several days until the female has deposited all her eggs. The young move downstream at night, shortly after they emerge.
CONSERVATION STATUS
Not listed by the IUCN. However, in May 2002 the National Marine Fisheries Service (under the Endangered Species Act) issued a ruling redefining the geographic range of the listed anadromous population of this species to include all steelheads and their progeny occurring in coastal river basins from the Santa Maria River (inclusive) to the United States/Mexico Border. Within the redefined geographic range, only anadromous, naturally spawned populations and their progeny, which reside below naturally occurring and man-made impassable barriers, such as impassable waterfalls and dams, are listed as endangered.
SIGNIFICANCE TO HUMANS
Perhaps the most often bred fish species in the world because of its adaptability and value as the subject of commercial and sports fisheries. Anglers find it very interesting because of its spectacular leaps and hard fighting when hooked.
Wikipedia
The rainbow trout, redband trout, or steelhead (Oncorhynchus mykiss) is a species of trout native to the Pacific Ocean and in North American rivers and lakes west of the Rocky Mountains. It also is native to parts of East Asia. Rainbow trout are now worldwide in distribution and are a highly prized game fish. They have been introduced to at least 45 countries, and every continent except Antarctica. However, in some of these locations, such as Australia, they have had very serious negative impacts on upland native fish species.
The naming of the rainbow trout species was based on fish taken from the San Leandro Creek drainage in Oakland, California. In 1855, Dr. Sean Taylor Spaulding, founder of the California Academy of Sciences, was given three specimens obtained from the creek. He described and assigned them the scientific name Salmo iridia. It was later determined that Spaulding and Matthew David Roberts were referring to the same species, and the original binomial name is now used to refer to the species.
Physical characteristics
Rainbow trout are unusual in that although can spend their entire life in fresh water, they are capable of migrating to sea water when conditions are right, though they must return to fresh water to breed.
The freshwater form is usually called "rainbow trout" or "redband trout", while the marine form is often called "steelhead", but these populations belong to the same species.
Rainbow trout are the smaller variety, found only in fresh water. Steelhead spend their adult lives in the ocean, but return to spawn in the streams in which they were born. They occur in cool streams up to 4,500 m in elevation.
Rainbows and steelhead have small black spots along their back, dorsal fin and caudal fin. Rainbows have a pink streak that runs from the gill cover to the caudal fin. The color of a rainbow's back varies from blue or green to a yellow-green or brown. Steelhead usually lack the pink stripe, except when young or spawning, and have chrome-colored sides. Rainbows are distinguished from their cousins, the cutthroat trout (Oncorhynchus clarki) by their short maxilla, which reaches to, but not past the rear margin of the eye. Rainbow trout also lack hyoid teeth, a feature present in cutthroat trout.
Rainbows range from 30 to 45 cm (12 to 18 inches) in length. Steelheads grow longer, ranging from 50 to 100 cm (20 to 40 inches) in length. Steelhead range in weight from 2.5 kg to 10 kg.
Lifecycle
Like salmon, steelhead are anadromous: they return to their original hatching ground to spawn. Different populations of steelheads migrate upriver at 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. Unlike salmon, steelhead are iteroparous and may make several spawning trips between fresh and salt water.
As food
Rainbow trout is popular in Western cuisine and is often farmed for food. It has tender flesh and a mild, somewhat nutty flavor. However, farmed trout and those taken from certain lakes have a pronounced muddy flavor which many people find unappealing; many shoppers therefore make it a point to ascertain the source of the fish before buying.
Clear Springs Foods, located near Buhl, Idaho, processes over 20 million pounds (9000 t) of rainbow trout each year, making it the world's largest producer.
Subspecies
A few populations are recognized as subspecies:
- California golden trout, Oncorhynchus mykiss aguabonita (Jordan, 1892).
- Columbia River redband trout, Oncorhynchus mykiss gairdnerii (Richardson, 1836).
- Kern golden trout, Oncorhynchus mykiss gilberti (Jordan, 1894).
- Coastal rainbow trout, Oncorhynchus mykiss irideus (Gibbons, 1955).
- Kamchatkan rainbow trout, Oncorhynchus mykiss mykiss (Walbaum, 1792).
- Baja California rainbow trout, Nelson's trout, or San Pedro Martir trout, Oncorhynchus mykiss nelsoni (Evermann, 1908).
- Great Basin redband trout, Oncorhynchus mykiss newberrii (Girard 1859)
- Sacramento golden trout, Oncorhynchus mykiss stonei (Jordan, 1894).
- Little Kern golden trout, Oncorhynchus mykiss whitei (Evermann, 1906).
References
- Oncorhynchus mykiss. FishBase. Ed. Ranier Froese and Daniel Pauly. February 2006 version. N.p.: FishBase, 2006.
- Oncorhynchus mykiss (TSN 161989). Integrated Taxonomic Information System. Accessed on 30 January 2006.
External links
- Rainbow trout page from the Alaska Department of Fish and Game
- Rainbow trout information from Northern State University