Rainbow trout, whose name refers to the many rainbow-colored spots on its skin, is the leading freshwater cultured species in Europe. Native to the Pacific coastal area in the United States, it was introduced into Europe at the end of the 19th century. Its hardiness and fast growth quickly proved particularly well adapted to aquaculture. Rainbow trout are farmed today in nearly all European countries, especially in coastal countries with a temperate climate.
Latin name – Oncorhynchus mykiss
Production (EU-27) – 204 745 t (2007), 31 % of global production
Value (EU-27) – EUR 539 million (2007)
Main EU producer countries – Italy, France, Denmark, Spain, Germany
Main producer countries worldwide – Chile, Norway, Turkey, Iran, USA.
Diagnostic Features
Elongate, fusiform body shape with 60 - 66 vertebrae, 3 - 4 dorsal spines, 10 - 12 dorsal soft rays, 3 - 4 anal spines, 8 - 12 anal soft rays, 19 caudal rays. Adipose fin present, usually with black edge. No nuptial tubercles but minor changes occur to the head, mouth and color in spawning males. Coloration blue to olive green above a pink band along the lateral line and silver below. Back, sides, head and fins covered with small black spots. Coloration varies with habitat, size, and sexual condition. Tendency for stream residents and spawners tend to be darker with more intense color, whereas lake residents are brighter and more silvery. Absence of hyoid teeth is the most easily distinguishing characteristic from cutthroat trout.
Habitat and Biology
The rainbow trout is a hardy fish that is easy to spawn, fast growing, tolerant to a wide range of environments and handling, and the large fry can be easily weaned on to an artificial diet (usually feeding on zooplankton). Capable of occupying many different habitats, ranging from an anadromous life history [strain known as steelhead] (living in the ocean but spawning in gravel-bottomed, fast-flowing, well-oxygenated rivers and streams) to permanently inhabiting lakes. The anadromous strain is known for its rapid growth, achieving 7 - 10 kg within 3 years, whereas the freshwater strain can only attain 4.5 kg in the same time span. The species can withstand vast ranges of temperature variation (0-27°C), but spawning and growth occurs in a narrower range (9 - 14°C). The optimum water temperature for rainbow trout culture is below 21°C. As a result, temperature and food availability influence growth and maturation, causing age at maturity to vary; though it is usually 3 - 4 years.
Females are able to produce up to 2000 eggs/kg of body weight. Eggs are relatively large in diameter (3 - 7mm). Most fish only spawn once, in spring (January-May), although selective breeding and photoperiod adjustment has developed hatchery strains that can mature earlier and spawn all year round. Superior characteristic selection is also achieved by cross breeding, increasing growth rates, resistance to disease, and prolificacy, and improving meat quality and taste. Genetic manipulation of the embryo sex chromosomes producing sterile, triploid females, hence avoiding the 'hook-like' jaw that does not appeal to the customer, and ensuring that introduced/escaped individuals cannot breed.
Trout will not spawn naturally in culture systems; thus juveniles must be obtained either by artificial spawning in a hatchery or by collecting eggs from wild stocks. Larvae are well developed at hatching. In the wild, adult trout feed on aquatic and terrestrial insects, mollusks, crustaceans, fish eggs, minnows, and other small fishes, but the most important food is freshwater shrimp, containing the carotenoid pigments responsible for the orange-pink color in the flesh. In aquaculture, the inclusion of the synthetic pigments astaxanthin and canthaxanthin in aqua feeds causes this pink coloration to be produced (where desired).
Market And Trade
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 fertilizer. The fresh fish market is large because the flesh is soft and delicate, white to pink in color with a mild flavor. Food market fish size can be reached in 9 months but 'pan-sized' fish, generally 280 - 400g, 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 color also vary globally with USA preferring white meat, but Europe and other parts of the world preferring pink meat generated from pigment supplements in aqua feed.
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.
Main issues
Trout farms inevitably impact upon the environment as river water is diverted from its natural course, potentially altering species composition and diversity. Escapee trout from farms can have negative impacts, potentially displacing endemic species (especially brown trout), and exhibiting aggressive behavior that results in the altering of fish community structure.
Impacts from flow-through systems are largely from disease treatment chemicals, uneaten feed and fish excreta, which can alter water and sediment chemistry downstream of the farm. Elevated nutrients reduce water quality (increasing biological oxygen demand, reducing dissolved oxygen and increasing turbidity) and increase the growth of algae and aquatic plants. Output restrictions require farms to have settling areas to remove solid wastes, though soluble phosphorous in the effluent cannot be removed economically - hence reductions in feed are needed to address the problem. There are also problems with the transmission of diseases from farmed stock to vulnerable wild populations.
FAO. © 2006-2011. Aquaculture topics and activities. Aquaculture. In: FAO Fisheries and Aquaculture Department [online]. Rome. Updated 18 July 2011. [Cited 12 September 2011]. http://www.fao.org/fishery/aquaculture/en
http://ec.europa.eu/fisheries/marine_species/farmed_fish_and_shellfish/trout/index_en.htm
Rainbow trout, whose name refers to the many rainbow-colored spots on its skin, is the leading freshwater cultured species in Europe. Native to the Pacific coastal area in the United States, it was introduced into Europe at the end of the 19th century. Its hardiness and fast growth quickly proved particularly well adapted to aquaculture. Rainbow trout are farmed today in nearly all European countries, especially in coastal countries with a temperate climate.
Latin name – Oncorhynchus mykiss
Production (EU-27) – 204 745 t (2007), 31 % of global production
Value (EU-27) – EUR 539 million (2007)
Main EU producer countries – Italy, France, Denmark, Spain, Germany
Main producer countries worldwide – Chile, Norway, Turkey, Iran, USA.
Diagnostic Features
Elongate, fusiform body shape with 60 - 66 vertebrae, 3 - 4 dorsal spines, 10 - 12 dorsal soft rays, 3 - 4 anal spines, 8 - 12 anal soft rays, 19 caudal rays. Adipose fin present, usually with black edge. No nuptial tubercles but minor changes occur to the head, mouth and color in spawning males. Coloration blue to olive green above a pink band along the lateral line and silver below. Back, sides, head and fins covered with small black spots. Coloration varies with habitat, size, and sexual condition. Tendency for stream residents and spawners tend to be darker with more intense color, whereas lake residents are brighter and more silvery. Absence of hyoid teeth is the most easily distinguishing characteristic from cutthroat trout.
Habitat and Biology
The rainbow trout is a hardy fish that is easy to spawn, fast growing, tolerant to a wide range of environments and handling, and the large fry can be easily weaned on to an artificial diet (usually feeding on zooplankton). Capable of occupying many different habitats, ranging from an anadromous life history [strain known as steelhead] (living in the ocean but spawning in gravel-bottomed, fast-flowing, well-oxygenated rivers and streams) to permanently inhabiting lakes. The anadromous strain is known for its rapid growth, achieving 7 - 10 kg within 3 years, whereas the freshwater strain can only attain 4.5 kg in the same time span. The species can withstand vast ranges of temperature variation (0-27°C), but spawning and growth occurs in a narrower range (9 - 14°C). The optimum water temperature for rainbow trout culture is below 21°C. As a result, temperature and food availability influence growth and maturation, causing age at maturity to vary; though it is usually 3 - 4 years.
Females are able to produce up to 2000 eggs/kg of body weight. Eggs are relatively large in diameter (3 - 7mm). Most fish only spawn once, in spring (January-May), although selective breeding and photoperiod adjustment has developed hatchery strains that can mature earlier and spawn all year round. Superior characteristic selection is also achieved by cross breeding, increasing growth rates, resistance to disease, and prolificacy, and improving meat quality and taste. Genetic manipulation of the embryo sex chromosomes producing sterile, triploid females, hence avoiding the 'hook-like' jaw that does not appeal to the customer, and ensuring that introduced/escaped individuals cannot breed.
Trout will not spawn naturally in culture systems; thus juveniles must be obtained either by artificial spawning in a hatchery or by collecting eggs from wild stocks. Larvae are well developed at hatching. In the wild, adult trout feed on aquatic and terrestrial insects, mollusks, crustaceans, fish eggs, minnows, and other small fishes, but the most important food is freshwater shrimp, containing the carotenoid pigments responsible for the orange-pink color in the flesh. In aquaculture, the inclusion of the synthetic pigments astaxanthin and canthaxanthin in aqua feeds causes this pink coloration to be produced (where desired).
Market And Trade
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 fertilizer. The fresh fish market is large because the flesh is soft and delicate, white to pink in color with a mild flavor. Food market fish size can be reached in 9 months but 'pan-sized' fish, generally 280 - 400g, 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 color also vary globally with USA preferring white meat, but Europe and other parts of the world preferring pink meat generated from pigment supplements in aqua feed.
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.
Main issues
Trout farms inevitably impact upon the environment as river water is diverted from its natural course, potentially altering species composition and diversity. Escapee trout from farms can have negative impacts, potentially displacing endemic species (especially brown trout), and exhibiting aggressive behavior that results in the altering of fish community structure.
Impacts from flow-through systems are largely from disease treatment chemicals, uneaten feed and fish excreta, which can alter water and sediment chemistry downstream of the farm. Elevated nutrients reduce water quality (increasing biological oxygen demand, reducing dissolved oxygen and increasing turbidity) and increase the growth of algae and aquatic plants. Output restrictions require farms to have settling areas to remove solid wastes, though soluble phosphorous in the effluent cannot be removed economically - hence reductions in feed are needed to address the problem. There are also problems with the transmission of diseases from farmed stock to vulnerable wild populations.
FAO. © 2006-2011. Aquaculture topics and activities. Aquaculture. In: FAO Fisheries and Aquaculture Department [online]. Rome. Updated 18 July 2011. [Cited 12 September 2011]. http://www.fao.org/fishery/aquaculture/en
http://ec.europa.eu/fisheries/marine_species/farmed_fish_and_shellfish/trout/index_en.htm