Small-scale rainbow trout farming Source FAO Fisheries and Aquaculture Keywords Water, farming, fish, trout Country of first practice General ID and publishing year 7492 and 2012 Sustainbale Development Goals Life below water

Summary The concept of this practice is to guide restaurants (Figure 2) and related services. the reader through the necessary basic The combination of short explanations information of both investment in and day- together with illustrations is aimed to-day operation of a small-scale rainbow for easy understanding. However, it is trout farm. suggested that users of this practice consult subject specialists, who will help to avoid Description unnecessary failures and their financial Trout farming is an ideal option for consequences. sustainable use of water resources in 1. Important trout species mountainous regions because here both There are 206 species in the family of surface and underground waters are suitable Salmonidae. Salmonids (salmon, trout, for this purpose. char and whitefish) are found in practically In regions where income-generating and all continents, partly because they are employment opportunities are scarce, trout indigenous there and partly because they farming could help to ensure employment have been introduced. Among trout, brook and steady incomes (Figure 1). In addition trout, brown trout, lake trout, sea trout and to the production, trout farming could also rainbow trout are the most widely known ensure increased income and employment species. Brown trout is native to Europe and through angling tourism, West Asia (Figure 3). An important market

Figure 1. Direct income generation through food production © FAO/TECA

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and sport fish, it has been introduced to northeast of the United States of America many different countries all over the world. and the east region of Canada. It has been According to their habitat, taxonomists introduced to many countries of South distinguish three forms of brown trout. They America, Oceania and Asia, and to practically are the actual brown trout (Salmo trutta m. all of the countries of Europe and the former fario), lake trout (Salmo trutta m. lacustris) Soviet Union. and sea trout (Salmo trutta m. trutta) 1.1 The rainbow trout (Figure 3). Rainbow trout (Oncorhynchus mykiss) is a Brook trout, together with lake trout highly commercial sport and market fish (Salvelinus namaycush), belongs to the (Figure 5). A normal adult rainbow trout “char” subgroup of salmonids, which weighs about 2 to 3 kg, while its maximum distinguishes it from trout and salmon. The size, weight and age are 120 cm total length brook trout is one of the most well-known (TL), 25.4 kg and 11 years, respectively. sport fish (Figure 5) and is native to the Rainbow trout live in the upper, cold water

Figure 2. Trout farming can support angling tourism and Supplying trout to local restaurants generates tourism © FAO/TECA

Figure 3. Brown, lake and sea trout

2 / 10 Figure 4. Brook trout (Salvelinus fontinalis)

Figure 5. Rainbow trout © FAO/TECA

Figure 6. Native range and international introductions of rainbow trout © FAO/TECA

sections of rivers and seas. As in the case of possessed advantageous qualities, such other trout, the habitat and food of rainbow as hardiness, fast growth, resistance to trout determine both their actual colour diseases and reliable reproduction under and shape. farm conditions. The rainbow trout has many local strains, In the wild, there are rainbow trout which have developed in the different populations that spawn in autumn and river systems. Out of these, numerous there are other populations that spawn improved commercial strains have been in spring. From these populations, two bred. The widely cultured commercial different commercial strains have been strains have been improved from those bred. Their qualities are similar, only their original rainbow trout populations that spawning seasons differ from each other.

3 / 10 Figure 7. Temperature ranges for rainbow trout at various stages © FAO/TECA

Figure 8. Clear water enables efficient feeding © FAO/TECA

This enables the production capacities of a • Clear water: keen eyesight is crucial for rainbow trout farm to be increased. In many the efficient feeding of trout (Figure 8). countries, the albino form of rainbow trout • Clean water: saturated with dissolved is cultured and is often, but mistakenly, oxygen (DO) in high concentrations called golden trout. This form is a popular (Figure 9) and free from harmful gases ornamental and “put-and- take” fish, and harmful solid materials produced even if it is very sensitive to unfavourable during metabolism and respiration environmental and production conditions. (Figure 10). 1.1.1 Native range and international • Rich water: water that contains enough introductions natural food (Figure 11). Rainbow trout is native to the cold water 1.1.3 Natural food rivers and lakes of the Pacific coasts of The actual natural food of rainbow North America and Asia. It has been trout depends on the age and size of introduced to about 82 countries (Figure fish, on the size of food item and on the 6), practically everywhere the conditions habitat occupied. Rainbow trout are are favourable for its culture, because aggressive and greedy in feeding. They are rainbow trout tolerates a wide range of opportunistic feeders that grab and eat environmental and production conditions almost anything. Figure 12 summarizes better than other trout species. the most frequent natural food items of 1.1.2 Habit factors rainbow trout. There are four vital habitat factors that Terrestrial insects are also consumed basically influence the growth of rainbow when they fall into the water. These trout: insects are adult beetles (Coleoptera), flies (Diptera), ants (Formicidae) and larvae of • Cold water: rainbow trout is a typical Lepidoptera (moths and butterflies). cold water fish (Figure 7).

4 / 10 Figure 9. High concentrations of dissolved oxygen enable smooth respiration © FAO/TECA

Figure 10. Trout need water that is free of harmful solid or gaseous waste materials © FAO/TECA

Figure 11. Most frequent natural food items of rainbow trout © FAO/TECA

5 / 10 Figure 12 The life cycle and development stages for rainbow trout in the wild © FAO/TECA

6 / 10 Figure 13. Standard measurements and body parts of rainbow trout © FAO/TECA

Figure 14. Correlation between the total length and the weight of rainbow trout © FAO/TECA

7 / 10 Figure 15. Duration of the development stages of rainbow trout © FAO/TECA

1.1.3 Life cycle and development stages in 1.1.5 Duration of the development stages wild Water temperature is a determining factor Figure 12 shows the life cycle and of fish production. This is because the development stages for rainbow trout in body temperature of embryos, fry and the wild. developing fish equalize their temperature 1.1.4 Measurements, body parts, organs to that of the water they are in. and correlations between length band Along with the body temperature, the weight intensity of the metabolism also changes. Figure 13 shows the standard The developing embryos and fry feed from measurements of body parts of a the yolk sac and receive oxygen through rainbow trout, while figure 14 shows the the entire body surface. When the water correlation between its total length and temperature is higher, the embryos and fry weight. develop more rapidly, while at lower water

8 / 10 temperatures the speed of development Central and Eastern Europe (CEE) and the reduces (Figure 15). Outside of a certain Caucasus and Central Asia (CCA). range of water temperature development Development of fry from swim-up fry stops. takes 1.5 to 3 months (Figure 16). For the The total length of the development sake of clear understanding and simple of embryo and fry from fertilization to calculations, “fry” in this technical paper swim-up is about 37 - 83 days at water refers to a total length of 5 cm and to an temperatures between 6 and 12°C. average body weight of 2 g. After starting external feeding, the actual Development of fingerlings from fry length of the development of the different takes 3 to 4.5 months (Figure 17).For the age groups depends not only on the sake of clear understanding and simple temperature and oxygen content of water calculations, “fingerling” in this technical but also on the quality and quantity of paper refers to a total length of 12.5 cm consumed feed. and to an average body weight of 25 g. In determining the following figures, it has Development of table fish from fingerling been assumed that trout is adequately fed takes 4 to 6.5 months (Figure 18). For the with commercial feeds, which are readily sake of clear understanding and simple and widely available in the countries of calculations, “table fish” in this technical

Figure 16. Development of fry

Figure 17. Development of fingerlings

9 / 10 Figure 18. Development of table fish

paper refers to the desired minimum body to 135 days) when the water temperature weight of 250 g. is between 5 and 15 °C. Growth of large table fish from 250 g to 500 g takes a further 2.5 to 4.5 months (75

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