(Salmon Trout, Steelhead Trout, or Coastal Rainbow Trout)
Physical Description and Taxonomy
Class: Osteichthyes
Order: Salmoniformes
Family: Salmonidae
Genus: Oncorhynchus
Species: mykiss
In 1992 the steelhead trout, Salmo gairdneri (the species named in memory of Meredith Gairdner, a 19th-century naturalist) was reclassified in the genus Oncorhynchus ("hooked nose"), and mykiss (a Siberian word for the species). There are two races, both native to Western North America. The common name of the freshwater O.m. is rainbow trout, a colorful game fish that has been transplanted worldwide. The sea-run, or anadromous rainbow trout is called steelhead, a word that entered the common nomenclature in the early 1880s.
Unlike salmon, steelhead can spawn several times, although the hydropower dams on the Columbia River system have interfered with that pattern, and the species has been classed as threatened under the Endangered Species Act. On December 12, 2000, biologists for the Yakama Indian Nation released the first of 110 revived and rehabilitated kelts—as between-spawning steelhead are called—into the Yakama and Columbia Rivers. All were wearing identification tags, clipped fins, and inch-long cylindrical radio transmitters in their throats, for tracking, DNA testing, and genetic research. Record-class steelhead can attain a length of up to 45 inches, and a weight of more than 40 pounds. (Lewis-Clark.org)
In 1989 both the genus name and specific name of the rainbow trout were changed (see Smith and Stearley 1989). Thousands of publications cite Salmo gairdneri as the name of the rainbow trout; now we call it Oncorhynchus mykiss. The genus name was changed from Salmo to Oncorhynchus partly based on fossil evidence because the Pacific trouts were thought to be more closely related to the Pacific salmon than to the Atlantic salmon [the name carrier or type of Salmo]. Pacific trout and salmon are now classified as Oncorhynchus. The species name gairdneri was changed to mykiss when it was thought that mykiss from Kamchatka, Russia, was the same as gairdneri; since mykiss was described first, that name had priority for use over gairdneri. (Fishbase.org)
Native Range/Habitat
Steelhead is a name given to rainbow trout which live in the Great lakes. Rainbow trout are native to the Pacific Ocean along North America and to rivers and other fresh waters of North America west of the Rocky Mountains. They are a popular game fish, and for this reason have been introduced all over the United States.
Temperature Requirements
Great lakes steelhead are usually found in waters less than 35 feet deep at temperatures of 58-62 degrees F. They are often found near stream outlets, especially in spring and early summer.
Feed/Diet
In the lake-dwelling part of their life cycle, they wander along the shoals eating plankton, minnows, surface and bottom insects and other aquatic life. Although they feed primarily in mid-depths, they do take surface insects, including fly fishermen's flies. Larger rainbows will eat other small fish if available.
Commercial Production
Steelhead are valiant fighters and their flesh is outstanding no matter how it is cooked. An unbeatable combination that makes them one of the most popular North American sport fish. (Michigan.gov)
The production of rainbow trout has grown exponentially since the 1950s, especially in Europe and more recently in Chile. This is primarily due to increased inland production in countries such as France, Italy, Denmark, Germany and Spain to supply the domestic markets, and mariculture in cages in Norway and Chile for the export market. Chile is currently the largest producer. Other major producing countries include Norway, France, Italy, Spain, Denmark, USA, Germany, Iran and the UK.
There are many outputs from rainbow trout culture, which include food products sold in supermarkets and other retail outlets, live fish for the restocking of rivers and lakes for recreational put-and-take game fisheries (especially in the USA, Europe and Japan), and products from hatcheries whose eggs and juveniles are sold to other farms.
Products for human consumption come as fresh, smoked, whole, filleted, canned, and frozen trout that are eaten steamed, fried, broiled, boiled, or micro-waved and baked. Trout processing wastes can be used for fish meal production or as fertiliser. The fresh fish market is large because the flesh is soft and delicate, white to pink in colour with a mild flavour. Food market fish size can be reached in 9 months but 'pan-sized' fish, generally 280-400 g, are harvested after 12-18 months. However, optimal harvest size varies globally: in the USA trout are harvested at 450-600 g; in Europe at 1-2 kg; in Canada, Chile, Norway, Sweden and Finland at 3-5 kg (from marine cages). Preferences in meat colour also vary globally with USA preferring white meat, but Europe and other parts of the world preferring pink meat generated from pigment supplements in aquafeed.
Strict guidelines are in place for the regulation of rainbow trout for consumption with respect to food safety. Hygiene and safe transportation of fresh fish are of paramount importance, to ensure that fish are uncontaminated by bacteria, in accordance with food agency directives.
Status and trends
The rainbow trout farming industry has been developing for several hundred years, and many aspects are highly efficient, using well-established systems. However, current research and development is continually attempting to increase production efficiency and sales by increasing rearing densities, improving recirculation technology, developing genetically superior strains of fish for improved growth, controlling maturation and gender, improving diets, reducing phosphorous concentrations of effluents, and developing better marketing. One method that has been developed is a genetically modified hormone that is effective in reducing production costs. However, problems may lie ahead as public opinion towards genetically-modified products continues to be negative. As production continues to rise research is needed to keep costs to a minimum so the industry can move forward. (FAO.ORG)
Spawning Requirements
Great Lakes steelhead enter their spawning streams from late October to early May. At the present most spawning occurs in the spring, although more steelhead are beginning to spawn in fall. Spawning takes place in a bed of fine gravel, usually in a riffle above a pool. Steelhead don't necessarily die after this; they may live to reproduce for as many as five successive years. Most rainbow trout return home to spawn in the stream in which they were born or planted.
Trout eggs hatch in four to seven weeks, depending on water temperature. Young trout may travel downstream to the lake in their first summer, or they may remain from one to three years in their home stream before migrating lakeward.
Individual growth varies greatly even within the same population. Most Great lakes steelhead reach sexual maturity at age three to five years, ahead of females. A mature 16-inch fish living in the Great lakes may continue to grow throughout its life and could reach 36 inches in length and up to 20 pounds in weight. However, average adult size for steelhead in 9 to 10 pounds while life expectancy in the Great Lakes is six to eight years.
Natural Enemies
Larger fish, fish-eating birds and mammals and sea lamprey are the steelhead's natural enemies. In turn, the steelhead finds itself competing with other salmon and trout, other predatory fishes and a variety of bottom feeders, for its food. It also competes with salmon and trout for spawning grounds. (Mich.gov)
There are a variety of diseases and parasites that can affect rainbow trout in aquaculture, which are summarised here. Prevention is the most important measure; good hatchery sanitation by restricting access, installing disinfectant footbaths and disinfecting equipment reduces the exposure of vulnerable fish to disease-causing agents.
In some cases antibiotics and other pharmaceuticals have been used in treatment but their inclusion in this table does not imply an FAO recommendation. (Cultured Aquatic Species Information Programme, Oncorhynchus mykiss)
References
Steelhead, Oncorhynchus mykiss, Michigan.gov
No comments:
Post a Comment