Rainbow trout production

Trout farm in Wales

Trout farm in France

Commercial production of rainbow trout in Croatia

River channel of a trout farm in Ohio

Rainbow trout while feeding

Trout in a basin

Trout seedlings in a rearing tank

Drawing of trout holding tanks

Spawning of rainbow trout

Salable rainbow trout

Portion trout

The trout production include not only the carp production of the world's most important branches of aquaculture .

Rainbow trout

Rainbow trout ( Oncorhynchus mykiss ) are among the most economically important fish in trout production due to their relatively simple keeping . This species has been breeding worldwide for over 100 years after its introduction from North America to Europe . The reasons for this are:

• high stress tolerance within the salmonids with low susceptibility to disease
• adapted for a wide range of water temperatures
• large genetic variation in a globally well-preserved gene pool
• great potential in product variation
• tasty meat with an attractive color and low fat content
• low FCR (feed conversion ratio), i.e. good feed conversion
• relatively high survival rate of the trout fry and inexpensive reproduction

Rainbow trout from around three kilograms in weight, pigmented meat and a silvery color are increasingly becoming an alternative to salmon for consumers.

economics

One of the most famous countries for producing rainbow trout is Denmark . Each year around 275 trout farms produce around 31,000 tons of fish in fresh water and 9,000 tons in sea water. Trout production in aquaculture has a share of around 20% in Denmark. 300 million trout eggs are exported worldwide. The value added is 40% in the entire Danish fisheries sector and has a market value of 900 million Danish kroner. Trout farms in Denmark are subject to the Statuary Order for Fish Farms and are subject to certain environmental regulations. In the years 2007-2013 aquaculture in Denmark grew to a production of 115,000 tonnes of fish, whereby the nitrate input through the fishery management could be reduced by 40% per kilogram of fish produced. The profitability of a trout farm is largely determined by the following factors: professionally designed system, equipment of high quality, experienced and well-trained staff, fish feed of high quality and proximity to the sales market. Market demand is achieved through product differentiation and thus achieving higher market prices. Buyers of trout farms can be consumers, fish processing companies, but also fishing clubs and fishing pond operators (put & take fishing ponds) for stocked fish. Trout production in some countries is organized according to a division of labor. Trout breeders and trout egg producing companies (e.g. AquaSearch ova Aps in Billund , or Troutex in Fredericia Denmark) supply fattening companies. The world's largest company in the production of rainbow trout is Clear Springs Foods in the US state of Idaho .

Production process

A basic distinction is made between classic pond management and closed circulation systems such as B. in plastic tanks (e.g. IRAS circulation systems with "nitrification" and "denitrification" in the breeding tank). Modern trout farms, especially in Denmark, are mostly based on the recirculation principle (FREA - Fully Recirculated Aquaculture).

Fish rearing

Trout on Danish farms are usually sexually mature at the age of three, milkers often as early as the age of two. Sexual maturity depends on hereditary disposition and the environmental conditions (feeding, light intensity, length of day, temperature, etc.) of the trout farm. Under natural conditions, the day length increases from January to June to 18 hours of daylight and six hours of darkness; with rising water temperatures from 7 ° C to 15 ° C. From a fishing perspective, trout that ripen late are preferable, because ripe fish (especially dairy farmers) are more aggressive, with a reduced daily gain and a declining meat quality. From a breeding perspective, a shortened ripening time is preferred as it shortens the generation interval and speeds up the entire breeding process. The breeding work focuses on inheritable factors, whereby the environmental conditions are kept as similar as possible. Parents that are important for breeding are marked with PIT tags. Both flow and water circulation systems are used in fish farming. The water is enriched with air and filtered to remove waste. The water temperature is kept at a constant 7 ° C. To kill pathogens which threaten the fry, can process for UV light - sterilization come to use. The fish spawn is incubated in incubators. Spawning is stimulated mechanically by the method of "stripping". The anesthetized Rogner is wiped off by hand and mixed with the milk (semen) in a container. The fertilized fish eggs are then incubated in the hatchery. Fish embryos can be recognized after approx. 25 days at a water temperature of 4 - 6 ° C. A Rogner can produce around 1,500 to 2,000 eggs per kilogram of live weight, around 10,000 eggs per liter. In order to reduce the failure rate (e.g. “Saprolegnia” fungal attack) in the fish embryos, disinfection should be carried out with formaldehyde solution . Young fish hatch out of the fish eggs and look for food in schools on the surface of the water. Spring or well water is ideal for avoiding pathogenic conditions. The young fish are fed with small granulate pellets (approx. 0.5 mm). The finger cots already have weights of approx. 5 grams. The pH value for the "finger cots" should be between 6.5 and 8. In the different stages of production, a distinction is made between fertilized fish eggs, eye training in fish eggs, brood with yolk sac, buoyant brood, brood fish, finger cots and portion trout ready for slaughter.

feeding

When feeding, trout farmers endeavor to counteract the seasonal fluctuations in biomass growth through appropriate feeding. The highest biomass increase is reached after six months of age, after which it decreases again. In trout feeding, the specific growth rate (SGR) is the determining factor:

• SGR = (exp ((InWt - InW0) / (T1 - T0)) - 1) * 100

W0: biomass at the beginning of the period; W1: biomass at the end of the period; T1 - T0: feeding days within the period The feed turnover rate (FCR) is determined as follows:

• FCR = fed feed (kg) / growth increase (kg)

According to Danish regulations, the FCR must not exceed 1.00. A distinction is made between controlled feeding and ad libitum feeding. In practice, controlled feeding has established itself, also to reduce the non-utilization of trout pellets. The following applies to the increase in protein: For one gram of protein, three grams of water are bound. Nowadays, feed computers control the daily rationed feed portion based on fish size, biomass, expected feed conversion, water temperature and possible fish diseases. Feeding makes up a large part of the cost factors in trout production. The feed composition and the content of protein , fat , carbohydrates , vitamins and minerals vary depending on the age and size of the trout. The lack of certain nutrients, such as B. essential amino acids can limit fish growth. Concentrated feed pellets are manufactured using the extrusion process. Their gross energy content should be at least 5.8 Mcal / kg. The greatest feed intake is achieved at water temperatures between 7 and 18 ° C. Food intake drops rapidly above 18 ° C.

Sanitary conditions and fish diseases

Epidemic fish diseases are a major economic threat to all intensively managed fish farms where useful fish are kept in confined spaces. The transport of fish eggs and fish within the EU is subject to certain legal conditions for fish quarantine. Veterinarians pay special attention to viruses such as B. the American viral disease, IHN (Infectious Haematopoietic Necrosis) or VHS (Viral Haemorrhagic Septicemia). In the EU, health categories from I (disease-free) to II (under surveillance) to V (infected) are assigned. Pathogens can be viruses, bacteria, fungi or parasites. Antibiotics and chemical additives are also used in trout farming to combat them. Trout fry are usually vaccinated prophylactically against Redmouth Disease (ERM). In Denmark, the use of antibiotics fell from 2,400 kilograms (2003) to 1,400 kilograms (2008). Slaked lime ( calcium hydroxide ), hydrogen peroxide , copper sulfate , chloramines , sodium carbonate and sodium chloride are often used as chemical additives, large amounts of which are formaldehyde . The use of formaldehyde as a hazardous and carcinogenic substance is viewed increasingly critically.

Traditional farming systems

A distinction is made between intensive and extensive cultivation. In traditional farming, production is completely dependent on external factors. Trout pond management is counted among the cold water cultures and is often located in mountainous regions due to the high oxygen demand of the fish. Trout ponds are traditionally created according to the flow system, in which the fresh water supply is ensured via a gradient, which is fed from a stream, river or lake. Rivers dammed up by dams were also used for commercial trout farming. The fish tanks can be ground-level ponds or concrete tanks (square or circular tanks). Flow channels (raceways) are also used. Originally, no wastewater treatment took place. Waste materials arise from fish droppings, the release of ammonia through the fish gills and the breakdown of unused feed at the bottom of the water. In 1989 the legislature passed new regulations on trout farming in Denmark. For example, ad libitum feeding was severely restricted and feed quality was specified. In addition, wet food and soft pellets were banned. Trout keepers were also asked to ensure that no large amounts of nutrients or chemical substances were introduced into the environment. The emission of nitrogen, phosphorus and organic matter must be documented. The oxygen content of the wastewater returned to the natural water must not fall below certain minimum levels. This has led to new, more environmentally friendly technologies and more efficient use of nutrients.

Modern farming systems

The strict environmental regulations in Denmark led to innovations in Best Available Technology (BAT). In modern trout farms there are a number of things to consider:

• Documentation on the management of environmental parameters
  • Nitrogen input ( nitrogen , nitrate and ammonia )
  • phosphorus
  • biological oxygen demand (BOD: Biochemical Oxygen Demand), the oxygen uptake of microorganisms at a water temperature of 20 ° C
  • chemical oxygen consumption (COD: Chemical Oxygen Demand) as a measure of the content of organic matter in water
  • Documentation on wastewater treatment
• Reduction of fresh water withdrawal
• Increase in the turnover of nutrients and organic material
• Non-impairment of neighboring waters (natural or wild waters)
• Increase in fish production without negative environmental impact
• Simplification of the administrative work

The following parameters are decisive for the profitability of trout farms: pond or pool material (concrete), water reflux (in percent), fish density (kg / m³), ​​water retention time in production units (h), daily feeding (kg), removal of sludge, decentralized sedimentation , disposal of organic waste, biofilters and plant lagoons. The following types of trout farms are distinguished:

• extensive trout farm with mechanical water treatment and water return
• intensive trout farm with mechanical and biological water treatment and less water consumption
• intensive trout farm with a high degree of innovation as a complete circular economy

The FREA (Fully Recirculated Aquaculture Facility) model offers a self-contained system. Modern trout farms offer the advantage of stable environmental conditions and little variation in water quality. Their disadvantages are an increased energy requirement for production per kilogram of fish, increased CO ₂ emissions and increased management and monitoring requirements. The water consumption of a traditional system is around 30 m³ per kilogram of fish produced, while very intensive trout farms use around 200 liters of fresh water per kilogram of fish produced. Between 2001 and 2004 the first organic trout farms in Denmark were established, which were subordinated to the principles of sustainable production.

breeding

The breeding technique for rainbow trout uses their high genetic variability and is usually a selective breed , i.e. H. the targeted selection of a certain type. Trout populations are built up according to the Gaussian normal distribution , which shows variances of certain desired characteristics. The heritability of these traits in the offspring determines the breeding success in classic elite breeding. The breeding progress is thus the product of selection intensity x selection severity x genetic variation. The breeding progress depends to a large extent on the trait, i.e. the desired performance characteristics of the trout, and the investment in elite breeding. Well-known breeding goals are an early achievement of the slaughter weight, improved product quality (fat content, content of omega-3 fatty acids , light or red meat color), salt water tolerance (through crossing with steelhead strains) and disease resistance.

The selective breeding takes place either through "natural selection", phenotypic mass selection, selection based on families, selection with the aid of markers (e.g. MAS or QTL ) or genomic selection (breeding value estimation). The “natural selection” method is often used in trout diseases with high mortality where there is high selection pressure. In the selection based on families, individual fish are selected whose siblings show the desired characteristics. The breeding program "Family Breeding Program with individual Tagging" begins with the characterization of certain properties such as FCR (feed conversion), SGR (specific growth rate), pigmentation or similar, followed by genetic evaluation according to individual indices and the 200 to 400 best Candidates with subsequent reproduction from 50 to 600 families / generation. Each of these families are kept separate (50 to 500 candidates / family weighing 10 to 50 grams) and tested for productivity under either laboratory or field conditions. Accordingly, there is also a “Family Breeding Program without individual tagging”. Geneticists currently see the greatest future opportunities in genomic selection, as the number of generation cycles is greatly reduced and with it the costs.

Transgenic trout

The production of transgenic fish is of particular economic interest because it is usually relatively easy to implement technically. Since the mid-1980s, 7.5 million euros have been invested in a total of eleven research projects in the EU on the subject of transgenic modifications in Atlantic salmon , tilapias and rainbow trout. In 2001, the Canadian company Seabright Corporation received the first patent (EP 0 578 653 B1) for Atlantic salmon and other species of accelerated growth fish produced in the USA , Canada and Chile . In addition to the speed of growth and the associated prematurity, meat quality, disease resistance and the improvement of frost tolerance (AFP: Antifreeze Protein) are further, economically important breeding goals. In order to prevent a “gene flow” into natural waters, sterile populations are often used. In "Fish Genetic Engineering" the following levels are distinguished:

• Design and construction of the artificial gene product (mostly structural genes that encode a certain protein or genes that determine growth hormones ) which is to be transferred to the respective fish species
• Gene transfer in fish eggs, mostly between fish species
• Identification of successfully transformed individuals (screening method for transgenic fish, e.g. with the help of marker genes)
• Determination of the transgenic gene expression ( regulators and promoters are required for transcription ) and phenotype
• Hereditary Studies
• Establishment of stable transgenic lines through artificial selection and breeding

More than 50% of research on transgenic salmonids deals with accelerated growth. This is done by transferring a gene construct for a growth hormone into fish eggs. This results in growth that is three to five times stronger, and in some individuals even 20 to 30 times stronger in an early growth phase. In salmon it was observed that their physiological adaptation to the seawater environment occurred two years earlier than in fish without the growth hormone. In rainbow trout, the increase in growth was 3.2 to 17.3 times that of a normally growing fish. Attempts have also been made to transfer genes from humans and rats which encode certain metabolic enzymes to rainbow trout . Only the first generation was observed. Due to the high degree of mosaics in the first generation, no significant change in the carbon exchange could be determined.

Genetic modification of Oncorhynchus mykiss (selection)

The aim of genetic modification	Reporter gene	Structural gene (target gene)	Promoter	reference
Increase in growth to shorten trout production time	no information	Ongh1, gene for growth hormone of the species Oncorhynchus	MT (metallothionine promoter)	Devlin et al. (2001)
Study on the development and gene expression of the grf / pacap gene, which codes for the two hormones GRF (hormone that releases growth hormone) and PCAP (adenylate cyclase-activating polypeptide ). Both hormones are involved in the release of growth hormone	1) Hypothalamus (hyp) -grf / pacap gene construct from sockeye salmon ( Oncorhynchus nerka ), which encodes the Pbluescript II KS +/-; 2) (pit) -grf / pacap gene construct from sockeye salmon “engineered” in a pUC19 vector	645 base pairs of the grf / pacap promoter region; gh promoter of king salmon ( Oncorhynchus tshawytscha )	Krueckl & Sherwood (2001)
Studies on the inhibitory effects of antisense - mRNA	Antisense sGnRH cDNA from Atlantic salmon ( Salmo salar ) cDNA; (GnRH: gonadotropin releasing hormone)	Pab promoter of the Atlantic salmon gnrh gene	Uzbekova et al. (2000)
Improvement of the carbohydrate metabolism of salmonids	1) hgluT1 (human glucose transporter type 1 c-DNA); 2) rhkII ( rat hexokinase type II cDNA)	1) CMV promoter ; 2) Sockeye salmon OnH3 histone 3 promoter; 3) OnMT-B (sockeye salmon metallothionein -B promoter	Pitkänen et al. (1999)
Growth enhancement	hgh (human growth hormone gene)	SV 40 promoter	Chourrot et al. (1986)
Production of sterile logs	Gonadotropin-releasing hormone antisense genes	Salmon histone 3	Smith et al. (2001)

Triploidy

In trout breeding, triploid trout, i. H. Trout with triple gene set, worked. Triploidy is achieved by exposing freshly fertilized trout eggs to heat and pressure surges (heat shock treatment or overpressure technology), which often results in triple sets of genes. The degree of ploidy influences growth behavior. These animals show strong growth in their development, which is not characterized by the regression of sexual maturity. This means that no energy is used for the development of germ cells, but only for length growth. Triploid rainbow trout can achieve slaughter weights of eight kilograms within three years. When kept, triploid trout have a higher oxygen requirement than diploid trout. Their susceptibility to stress is also greater. These fish often show growth deformations such as spinal curvature, heart and eye diseases, etc. Triploid individuals cannot reproduce. An investigation had shown that due to the degree of ploidy in the genome, no conclusions could be drawn about the survival and growth rates of trout. Compared to the diploid trout, triploid trout showed a higher feed consumption per kilogram gain, a more compact body shape and a higher net carcass yield. The US company Troutlodge Inc. sells triploid rainbow trout from all-female monosex populations.

Environmental influences

Trout production, especially pond farming with its connection to natural wild waters, is exposed to a number of environmental influences. The maximum annual feed consumption must be determined, as well as the water input (water extraction from the groundwater or water extraction from neighboring rivers), the amount of nutrients absorbed and waste materials (such as organic suspended matter, fish droppings, etc.) from trout production, the oxygen saturation of the Water at the outlet and the maximum input of antibiotics and chemical additives (growth hormones etc.). To date, there are few biosafety studies on the release of transgenic fish into wild waters and their possible hybridization. Larger male specimens from a transgenic line whose growth in size has been manipulated usually have a mating advantage in females over competing males from the wild population. William Muir and Richard Howard from Purdue University are investigating the “gene flow” from aquaculture into wild waters using “fitness components”, which allow statements to be made about the possible adaptation of transgenic fish in natural waters. As part of the Bergen Declaration on the occasion of the 5th International North Sea Protection Conference in March 2002, it was proposed to minimize the ecological risk of an outbreak of transgenic fish by building aquaculture holding systems only terrestrially without connection to a natural body of water.

Web links

• Torben Nielsen: The Future of Rainbow Trout Breeding, AquaSearch ova (English, PDF)
• András Woynarovich, György Hoitsy, Thomas Moth-Poulsen: Small Scale Rainbowtrout Farming, FAO Fisheries and Aquaculture Technical Paper (PDF) 561 (English), Rome, 2011
• Alfred Jokumsen, Lars M. Svendsen: Farming of Freshwater Rainbow Trout in Denmark 2010 (English)
• Ecological fish production: structure, development, problems, need for political action (PDF)

Individual evidence

1. ↑ ^{a b c d e f g h i j k l m n o} The Future of Rainbowtrout Breeding, Torben Nielsen, AquaSearch ova ( Memento of the original from March 6, 2014 in the Internet Archive ) Info: The archive link was inserted automatically and not yet checked. Please check the original and archive link according to the instructions and then remove this notice. 
2. ↑ ^{a b c d e} Homepage of the Danish aquaculture company Aquasearch
3. ↑ ^{a b c d e f g h i j k l m n o p q r s t u v w x y z aa from} Alfred Jokumsen and Lars M. Svendsen: Farming of Freshwater Rainbow Trout in Denmark, 2010
4. ↑ ^{a b c d e} Recirculated Aquaculture by Thomas Moth-Poulsen ( Memento of the original from July 1, 2014 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. 
5. ↑ Homepage of the Danish aquaculture company Troutex
6. ^ Homepage of the company Clear Springs Foods
7. ↑ Visit Idaho, Clear Springs Foods Inc. at Twin Falls on the Snake River ( Memento from August 15, 2015 in the Internet Archive )
8. ↑ Agintec, fish farming recirculation systems, diagram of a recirculation system
9. ↑ passive integrated transponder
10. ^ Bavarian State Institute for Agriculture, Breeding and Breeding of Trout
11. ^ ^{A b c d} András Woynarovich, György Hoitsy and Thomas Moth-Poulsen: Small Scale Rainbowtrout Farming, FAO Fisheries and Aquaculture Technical Paper, 561, Rome, 2011
12. ↑ Rotmund's Disease
13. ↑ Water residence time in production unit
14. ↑ in the drain to fix nitrogen in aquatic plants
15. ↑ marker aided selection
16. ↑ Bavarian State Institute for Agriculture, Genomic Selection, by Dr. Reiner Emmerling, Dr. Christian Edel, December 2012
17. ↑ ^{a b c d e f g h i} Jennifer Teufel, Frank Pätzold and Christof Potthof: Specific research on transgenic fish considering especially the biology of trout and salmon, Öko-Institut eV, Institute for Applied Ecology, Freiburg, Pätzold Gewässerökologie, Baden- Baden ( Memento of the original from January 24, 2012 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. 
18. ^ Gene construct for the production of transgenic fish, The Super Salmon Case
19. ↑ for example the metallothionin promoter (rtMT) from Oncorhynchus mykiss
20. ↑ William J. Thieman, Michael A. Palladino: Biotechnology - Biotechnology - Relevant for practice and current (= Pearson Studies - Biology ), Addison-Wesley Verlag, 2007, ISBN 978-3-8273-7236-9 , Aquatic Biotechnology , p. 295 .
21. ^ Fish in aquaculture, Albert Schweitzer Foundation for our environment
22. ↑ A. Müller-Belecke, Sabine Gebhardt, C. Werner, K. Poontawee, M. Wicke and Gabriele Hörstgen-Schwark: Comparison of fattening performance and carcass composition of diploid and triploid portion trout (Oncorhynchus mykiss) under practical conditions
23. ^ Homepage of the US company Troutlodge Inc., Bonney Lake, Washington State / USA
24. ↑ No Sex on the Beach, Gen-Ethical Network ( Memento of the original from March 17, 2014 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. 
25. ↑ Transgenic fish could threaten wild populations, 2000
26. ↑ Bergen Declaration, Fifth International Conference on the Protection of the North Sea ( Memento of the original of July 7, 2011 in the Internet Archive ) Info: The archive link has been inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.