**3. Domestication of diadromous and marine fish species**

#### **3.1. The Atlantic salmon (***Salmo salar***)**

The farming of the Atlantic salmon started in the early nineteenth century in the United Kingdom in order to rebuild river populations for angling [9]. Nevertheless, this is only at the end of the 1960s that the farming in sea cages was used for the first time in Norway [57]. From the year 1970, the first ever family-based breeding program of the Atlantic salmon was initiated in Norway in a brand new research institute entitled AKVAFORSK [57, 58]. Even though the production of the Atlantic salmon was only 100 tons in Norway at this time, the equivalent of about 3.6 million US\$ was covered for two-thirds by the Norwegian government and the rest by industry (not working in the aquaculture field) and nongovernmental organizations [57]. In parallel, research programs were started to develop new dry pellet feed adapted to the Atlantic salmon, which were available from 1982 [57]. After about 40 years of farming, the time to produce a standard market-sized 4 kg fish has been halved, and while 3 kg of dry matter (in moist feed) was necessary to produce 1 kg of salmon in the beginning, this has also been reduced to 1.15 kg (dry pellets) [37]. Other traits were progressively added to the selection index such as age at sexual maturity, disease resistance, stress resistance, and quality of the flesh [10, 37, 57, 58]. From the early stages of the selective breeding programs, eggs and juveniles were sold to the industry resulting in that close to 100% of the production of the Atlantic salmon in Norway and in the rest of the world are now based on improved stocks [10, 57, 58]. Farmed salmon is regarded as one of the most domesticated fish species farmed for food, and one Norwegian strain has been exposed to ≥12 generations of domestication [59, 60].

produce the Atlantic salmon, among which the four leading countries are Norway, Chile, the United Kingdom, and Canada [19, 47, 62]. In Norway and Chile (where this species was introduced), the farming of the Atlantic salmon has an enormous economic importance [63, 64]. In Norway, the farming of Atlantic salmon is the third largest industry after petroleum and mining [47]. In Chile, the exports of the Atlantic salmon represent about two-thirds of the total Chilean fisheries exports and became the third most important export commodity after copper and wood products [47]. Most part of the production (on-growing) is now performed in sea cages [19, 61], with hatcheries working with either flow-through or recirculating aqua-

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The Atlantic salmon has evolved in few decades from a luxury item, which was consumed only at specific periods in the year (particularly at Christmas), to convenience products [9]. He has become in 2014 the ninth most produced aquatic products globally, with more than 2.3 million tons. The success of its farming in Norway (and in Chile) is mainly due to the presence of numerous suitable sites for its production, a dynamic research and industry as well as government support [9]. Besides, the Atlantic salmon displays several features (high growth in cages, flesh strongly appreciated by consumers, etc.) that contribute to its farming success [9]. In parallel, the capture by fisheries has strongly decreased from 118,000 tons in 1980 to 73,000 tons in 1990 to less than 40,000 ton in 2000 [47]. Today, almost 100% of the Atlantic salmon is

The traditional farming of the European seabass in the Mediterranean Sea consisted of collecting juveniles in the wild and releasing them in semi-artificial coastal lagoons, such as "Vallicoltura" in Italy [66, 67]. Within these lagoons, seabass was reared extensively [68]. Nevertheless, from the year 1960, in the face of strong competition for wild juveniles between the on-growers and the decrease of natural resources [66], the first rearing trials were initiated in France and Italy [69]. In the middle of the 1980s, the development of reliable methods of reproduction techniques and husbandry methods allowed higher survival [68], and their diffusion rapidly led to the development of a true industry in several countries along the Mediterranean Sea [66, 68]. In the 1990s, the first breeding programs were initiated, first in France and Israel, then in Greece, Spain, and Italy, which allow obtaining the eighth generation of selection in the oldest program [67]. However, a large proportion of the broodstock used today is still coming from wild breeders or first-generation individuals

The aquaculture production of seabass was almost inexistent in 1950 (**Figure 7**). With the control of the life cycle in captivity, the aquaculture production increased exponentially from the middle of 1980 to reach 134,711 tons in 2010 (**Figure 7**). In the same period of time, the capture by fisheries increased from 4460 tons in 1980 to 10,853 tons in 2010 [9]. Consequently, 9 of 10 seabasses consumed in the world are now farmed. The main producers are all located around the Mediterranean Sea: Turkey, Greece, Egypt, Spain, and Italy [9]. Most of the production (on-growing) is realized in sea cages, followed by tanks and lagoon [68].

culture systems [65].

coming from farming [47].

[66, 69, 70].

**3.2. The European seabass (***Dicentrarchus labrax***)**

In parallel to its domestication, the production was multiplied by 5000 (**Figure 6**) from 294 tons in 1970 to more than 1.4 million tons in 2010 [19, 61]. A dozen of countries currently

**Figure 6.** Global aquaculture production from 1950 to 2016 of the Atlantic salmon *Salmo salar* (data from the FAO database).

produce the Atlantic salmon, among which the four leading countries are Norway, Chile, the United Kingdom, and Canada [19, 47, 62]. In Norway and Chile (where this species was introduced), the farming of the Atlantic salmon has an enormous economic importance [63, 64]. In Norway, the farming of Atlantic salmon is the third largest industry after petroleum and mining [47]. In Chile, the exports of the Atlantic salmon represent about two-thirds of the total Chilean fisheries exports and became the third most important export commodity after copper and wood products [47]. Most part of the production (on-growing) is now performed in sea cages [19, 61], with hatcheries working with either flow-through or recirculating aquaculture systems [65].

The Atlantic salmon has evolved in few decades from a luxury item, which was consumed only at specific periods in the year (particularly at Christmas), to convenience products [9]. He has become in 2014 the ninth most produced aquatic products globally, with more than 2.3 million tons. The success of its farming in Norway (and in Chile) is mainly due to the presence of numerous suitable sites for its production, a dynamic research and industry as well as government support [9]. Besides, the Atlantic salmon displays several features (high growth in cages, flesh strongly appreciated by consumers, etc.) that contribute to its farming success [9]. In parallel, the capture by fisheries has strongly decreased from 118,000 tons in 1980 to 73,000 tons in 1990 to less than 40,000 ton in 2000 [47]. Today, almost 100% of the Atlantic salmon is coming from farming [47].

#### **3.2. The European seabass (***Dicentrarchus labrax***)**

**3. Domestication of diadromous and marine fish species**

The farming of the Atlantic salmon started in the early nineteenth century in the United Kingdom in order to rebuild river populations for angling [9]. Nevertheless, this is only at the end of the 1960s that the farming in sea cages was used for the first time in Norway [57]. From the year 1970, the first ever family-based breeding program of the Atlantic salmon was initiated in Norway in a brand new research institute entitled AKVAFORSK [57, 58]. Even though the production of the Atlantic salmon was only 100 tons in Norway at this time, the equivalent of about 3.6 million US\$ was covered for two-thirds by the Norwegian government and the rest by industry (not working in the aquaculture field) and nongovernmental organizations [57]. In parallel, research programs were started to develop new dry pellet feed adapted to the Atlantic salmon, which were available from 1982 [57]. After about 40 years of farming, the time to produce a standard market-sized 4 kg fish has been halved, and while 3 kg of dry matter (in moist feed) was necessary to produce 1 kg of salmon in the beginning, this has also been reduced to 1.15 kg (dry pellets) [37]. Other traits were progressively added to the selection index such as age at sexual maturity, disease resistance, stress resistance, and quality of the flesh [10, 37, 57, 58]. From the early stages of the selective breeding programs, eggs and juveniles were sold to the industry resulting in that close to 100% of the production of the Atlantic salmon in Norway and in the rest of the world are now based on improved stocks [10, 57, 58]. Farmed salmon is regarded as one of the most domesticated fish species farmed for food, and

one Norwegian strain has been exposed to ≥12 generations of domestication [59, 60].

In parallel to its domestication, the production was multiplied by 5000 (**Figure 6**) from 294 tons in 1970 to more than 1.4 million tons in 2010 [19, 61]. A dozen of countries currently

**Figure 6.** Global aquaculture production from 1950 to 2016 of the Atlantic salmon *Salmo salar* (data from the FAO database).

**3.1. The Atlantic salmon (***Salmo salar***)**

78 Animal Domestication

The traditional farming of the European seabass in the Mediterranean Sea consisted of collecting juveniles in the wild and releasing them in semi-artificial coastal lagoons, such as "Vallicoltura" in Italy [66, 67]. Within these lagoons, seabass was reared extensively [68]. Nevertheless, from the year 1960, in the face of strong competition for wild juveniles between the on-growers and the decrease of natural resources [66], the first rearing trials were initiated in France and Italy [69]. In the middle of the 1980s, the development of reliable methods of reproduction techniques and husbandry methods allowed higher survival [68], and their diffusion rapidly led to the development of a true industry in several countries along the Mediterranean Sea [66, 68]. In the 1990s, the first breeding programs were initiated, first in France and Israel, then in Greece, Spain, and Italy, which allow obtaining the eighth generation of selection in the oldest program [67]. However, a large proportion of the broodstock used today is still coming from wild breeders or first-generation individuals [66, 69, 70].

The aquaculture production of seabass was almost inexistent in 1950 (**Figure 7**). With the control of the life cycle in captivity, the aquaculture production increased exponentially from the middle of 1980 to reach 134,711 tons in 2010 (**Figure 7**). In the same period of time, the capture by fisheries increased from 4460 tons in 1980 to 10,853 tons in 2010 [9]. Consequently, 9 of 10 seabasses consumed in the world are now farmed. The main producers are all located around the Mediterranean Sea: Turkey, Greece, Egypt, Spain, and Italy [9]. Most of the production (on-growing) is realized in sea cages, followed by tanks and lagoon [68].

industry is entirely based on the stocking of wild-caught specimens, which are reared in cages

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Despite the lack of control of the full life cycle in captivity, the aquaculture production has evolved very quickly from the year 1990 to reach 4080 tons in 2010 (**Figure 8**). More than 10 countries around the Mediterranean Sea currently produce this species, that is, around 60–70 farms [72 - 74]. The leading producers are Croatia, Malta, Turkey, Spain, and Tunisia [77, 78]. The first kind of production, which dates back to the 1980s, is based on the capture of breeders, whose weight varies between 40 and 400 kg, during the migration season, most often close to the spawning areas [73]. Those large individuals are then transported at low speed (1–1.5 knots) over distances ranging from few to 100 km, which might sometimes take several weeks, before being transferred to very large sea cages [73, 79]. Within those very large rearing cages, which may reach 50–60 m of diameter (sometimes even larger than 100 m) and 20–35 m deep, fish are fattened during several months, time required to rebuild muscle fat content that confers to the high-quality flesh researched on the Japanese market of sushi and sashimi [71, 73, 76]. During the middle of 1990s, a second type of production was initiated and consists of capturing immature individuals (8–20 kg in body weight), which are then reared during about 2–3 years in smaller sea cages than for breeders (50–60 m of diameter for about 20 m deep) to get fish of 30–50 kg [73, 76]. This type of production is mainly developed in the Adriatic Sea, particularly in Croatia [71, 76]. In all rearing systems, tunas are most often feed small forage fishes, among which sardinella (*Sardinella aurita*), pilchard (*Sardina pilchardus*), herring (*Clupea harengus*), mackerel (*Scomber scombrus*), chub mackerel (*Scomber japonicas*), horse mackerel (*Trachurus* sp.), bogue (*Boops boops*), and some cephalopods [71, 73, 75, 78, 79]. The feed conversion rates, which are estimated on a wet feed/wet tuna biomass, are most often high and vary between 10 and 20:1 [73, 78]. In other words, it requires 20 kg of forage fish to make 1 kg of tuna [73]. These feed conversion rates may be even beyond 40:1 for large specimens [73]. Two close relative species to the Atlantic bluefin tuna are also currently produced in other geographic areas using similar methods, namely the Northern Pacific bluefin tuna (*Thunnus orientalis*) in Mexico [78, 79] and the Southern bluefin tuna (*Thunnus maccoyii*) in Australia [80]. In 2002, Japanese scientists were able to obtain eggs and larvae of *T. orientalis* in an artificial setting; yet, there is not a broad knowledge of how to culture tuna in captive conditions, and much research is

during a period varying from few months to 2 or 3 years [72–76].

needed to consistently control the entire life cycle in captivity [78].

wild stocks [72, 73, 80].

**4. Conclusions**

In conclusion, the aquaculture production of Atlantic bluefin tuna has strongly increased within the past two decades, mainly driven by the Japanese market [78], its high commercial value associated with its high growth (30 kg in 3 years) [73]. However, the production of this species is based on the capture of wild individuals in nature; thus, only a control of the entire life cycle could ensure the sustainability of the industry through a reduction in its reliance on

The strong increase of the aquaculture production since the early 1980s has relied chiefly on the domestication of an increasing number of fish species [12, 13, 81–85]. Nevertheless, only a limited number has reached a high level of domestication (**Table 1**), such as the rainbow trout,

**Figure 7.** Global aquaculture production from 1950 to 2016 of the seabass *Dicentrarchus labrax* (data from the FAO database).

The seabass has become in less than three decades the second most produced fish species in the Mediterranean Sea, just after the sea bream *Sparus aurata* (whose production has followed a similar trend).

#### **3.3. The Atlantic bluefin tuna (***Thunnus thynnus***)**

The farming of the Atlantic bluefin tuna is recent [9]. The first trials of farming date back to the 1970s in Canada, Japan, and Australia [71]. Nevertheless, the aquaculture production truly started in the middle of the 1980s in the Mediterranean Sea, with the evolution of new technics allowing to provide fish to fattening farms [71, 72]. Despite significant progress, notably thanks to the work of a consortium of European researchers, the reliable control of the life cycle of the Atlantic bluefin tuna in captivity was never reached [73, 74]. Consequently, this

**Figure 8.** Global aquaculture production from 1950 to 2016 of the Atlantic bluefin tuna *Thunnus thynnus* (data from the FAO database).

industry is entirely based on the stocking of wild-caught specimens, which are reared in cages during a period varying from few months to 2 or 3 years [72–76].

Despite the lack of control of the full life cycle in captivity, the aquaculture production has evolved very quickly from the year 1990 to reach 4080 tons in 2010 (**Figure 8**). More than 10 countries around the Mediterranean Sea currently produce this species, that is, around 60–70 farms [72 - 74]. The leading producers are Croatia, Malta, Turkey, Spain, and Tunisia [77, 78]. The first kind of production, which dates back to the 1980s, is based on the capture of breeders, whose weight varies between 40 and 400 kg, during the migration season, most often close to the spawning areas [73]. Those large individuals are then transported at low speed (1–1.5 knots) over distances ranging from few to 100 km, which might sometimes take several weeks, before being transferred to very large sea cages [73, 79]. Within those very large rearing cages, which may reach 50–60 m of diameter (sometimes even larger than 100 m) and 20–35 m deep, fish are fattened during several months, time required to rebuild muscle fat content that confers to the high-quality flesh researched on the Japanese market of sushi and sashimi [71, 73, 76]. During the middle of 1990s, a second type of production was initiated and consists of capturing immature individuals (8–20 kg in body weight), which are then reared during about 2–3 years in smaller sea cages than for breeders (50–60 m of diameter for about 20 m deep) to get fish of 30–50 kg [73, 76]. This type of production is mainly developed in the Adriatic Sea, particularly in Croatia [71, 76]. In all rearing systems, tunas are most often feed small forage fishes, among which sardinella (*Sardinella aurita*), pilchard (*Sardina pilchardus*), herring (*Clupea harengus*), mackerel (*Scomber scombrus*), chub mackerel (*Scomber japonicas*), horse mackerel (*Trachurus* sp.), bogue (*Boops boops*), and some cephalopods [71, 73, 75, 78, 79]. The feed conversion rates, which are estimated on a wet feed/wet tuna biomass, are most often high and vary between 10 and 20:1 [73, 78]. In other words, it requires 20 kg of forage fish to make 1 kg of tuna [73]. These feed conversion rates may be even beyond 40:1 for large specimens [73]. Two close relative species to the Atlantic bluefin tuna are also currently produced in other geographic areas using similar methods, namely the Northern Pacific bluefin tuna (*Thunnus orientalis*) in Mexico [78, 79] and the Southern bluefin tuna (*Thunnus maccoyii*) in Australia [80]. In 2002, Japanese scientists were able to obtain eggs and larvae of *T. orientalis* in an artificial setting; yet, there is not a broad knowledge of how to culture tuna in captive conditions, and much research is needed to consistently control the entire life cycle in captivity [78].

In conclusion, the aquaculture production of Atlantic bluefin tuna has strongly increased within the past two decades, mainly driven by the Japanese market [78], its high commercial value associated with its high growth (30 kg in 3 years) [73]. However, the production of this species is based on the capture of wild individuals in nature; thus, only a control of the entire life cycle could ensure the sustainability of the industry through a reduction in its reliance on wild stocks [72, 73, 80].

### **4. Conclusions**

**Figure 8.** Global aquaculture production from 1950 to 2016 of the Atlantic bluefin tuna *Thunnus thynnus* (data from the

The seabass has become in less than three decades the second most produced fish species in the Mediterranean Sea, just after the sea bream *Sparus aurata* (whose production has fol-

**Figure 7.** Global aquaculture production from 1950 to 2016 of the seabass *Dicentrarchus labrax* (data from the FAO

The farming of the Atlantic bluefin tuna is recent [9]. The first trials of farming date back to the 1970s in Canada, Japan, and Australia [71]. Nevertheless, the aquaculture production truly started in the middle of the 1980s in the Mediterranean Sea, with the evolution of new technics allowing to provide fish to fattening farms [71, 72]. Despite significant progress, notably thanks to the work of a consortium of European researchers, the reliable control of the life cycle of the Atlantic bluefin tuna in captivity was never reached [73, 74]. Consequently, this

FAO database).

lowed a similar trend).

database).

80 Animal Domestication

**3.3. The Atlantic bluefin tuna (***Thunnus thynnus***)**

The strong increase of the aquaculture production since the early 1980s has relied chiefly on the domestication of an increasing number of fish species [12, 13, 81–85]. Nevertheless, only a limited number has reached a high level of domestication (**Table 1**), such as the rainbow trout, the Nile tilapia, or the Atlantic salmon [83–85]. The 35 species classified at Level 5 [12] belong to 10 families, among which Cyprinidae (*n* = 10 species), Salmonidae (*n* = 8), and Acipenseridae (*n* = 5) [83]. For these species, the entire life cycle is controlled in captivity, and breeding programs have allowed improving, among others, growth, with average genetic gains comprised between 10 and 15% per generation [37, 58, 85–87]. Today, it is estimated that about 10% of the global production is based on improved individuals [37, 87–89]. Nevertheless, very often, even for the species that have reached Level 4 or 5 (**Table 1**), a significant part of global production is based on the introduction of wild individuals. Conversely to these few domesticated species, or more accurately domesticated populations, the majority of farmed fish species still rely on the regular inputs of wild individuals (**Table 1**); thus, there is no strong dichotomy within the same species between wild individuals (coming from fisheries) and farmed individuals (produced in aquaculture) [90–93]. Besides, for numerous species, aquaculture is not a true alternative to capture fisheries but rather a mean to produce wild individuals to a certain commercial size by strongly decreasing the high-mortality rate characteristics of wild populations [90, 94]. Most farmed fish are thus still relatively similar to their wild congeners [95, 96].

intensity level of farming, from extensive to highly intensive, and industrialization are also very diverse [18]. From an activity mainly artisanal, aquaculture has evolved to include very large companies that export in numerous countries [17, 103]. According to FAO, the annual production by fish farmer also strongly varies from less than 1 ton in Indonesia to 4 tons in

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India, 7 tons in China, 35 tons in Chile, and 187 tons in Norway [19].

Address all correspondence to: fabrice.teletchea@univ-lorraine.fr

[1] Nash CE. The History of Aquaculture. Chichester. Wiley-Blackwell; 2011. 244 p

[3] Harache Y. Development and diversification issues in aquaculture. A historical and dynamic view of fish culture diversification. Cahiers Options Méditerranéennes.

[4] Diana JS, Egna HS, Chopin T, Peterson MS, Cao L, Pomeroy R, Verdegem M, Slack WT, Bondad-Reantaso MG, Cabello F. Responsible aquaculture in 2050: Valuing local condi-

[5] Balon EK. Origin and domestication of the wild carp, *Cyprinus carpio*: From roman gour-

[6] Liao IC, Huang YS. Methodological approach used for the domestication of potential candidates for aquaculture. Cahiers Options Méditerranéennes. 2000;**47**:97-107

[7] Gjedrem T, Baranski M. Selective breeding in aquaculture: An introduction. In: Reviews: Methods and Technologies in: Fish Biology and Fisheries. Vol. 10. Springer; 2009. 221 p

[9] Teletchea F. De la pêche à l'aquaculture. Demain, quels poissons dans nos assiettes?

tions and human innovations will be key to success. Bioscience. 2013;**63**:255-262

mets to the swimming flowers. Aquaculture. 1995;**129**:3-48

[8] Pinchot GB. Marine farming. Scientific American. 1970;**223**:15-21

Paris: Editions Belin; Basel. 2016. 180 p. ISBN: 978-2701164397

Université de Lorraine, Inra, URAFPA, Nancy, France

[2] Cressey D. Future fish. Nature. 2009;**458**:398-400

**Conflict of interest**

**Author details**

Teletchea Fabrice

**References**

2002;**59**:15-23

The author declares no conflict of interest.

Even though the number of farmed aquatic species (including fish, molluscs, and crustaceans) has strongly increased from 1950 to 2010, from about 72 to more than 500 [19, 20], only few species ensure the bulk of the production today [30, 83, 97]. For fish only, 15 species ensure more than 85% of the global production in 2005 [30], despite the number of farmed species rose from 43 to 219 between 1950 and 2005 [97]. In 2009, this trend was confirmed with more than 90% of the global production relying on 20 species only [83]. Only in Europe, most of the aquaculture production is based on the rearing of 10 species only [34, 98]. For some species, which have a very high production today, their farming is quite recent, dating back only to two or three decades only, such as the striped catfish or the Atlantic salmon [30, 97]. Among the 33 species with more than 100,000 tons in 2005, about one-quarter was not produced 40 years ago [97], which illustrates that new species can contribute strongly to the global production [99–101]. Conversely, most farming trials of new species realized within the past decades, either failed or resulted in low production volumes, about tens of tons. This demonstrates how difficult it is to farm a new species, whose development depends on the interaction of various factors, among which biological (availability of wild individuals, ability to control the life cycle in captivity), economical (acceptability by consumers, competition with other animal products), and environmental ones (availability of suitable sites and water, competition with other resources) [12, 18, 84, 91]. More recently, it has also become evident that climate change, which may result, among others, in global warming, saline water intrusion, and ocean acidification, may affect aquaculture [102]. Therefore, aquaculture should use genetically improved and robust animals not suffering from inbreeding depression, resulting from well-managed selective breeding programs with proper inbreeding control and breeding goals [102]. The leading species for aquaculture production have been extensively introduced across the world, particularly in the past century, resulting in that the bulk of aquaculture production relied on the farming of these very few alien species in numerous countries [11, 15]. Yet, the contribution of native species to global aquaculture will perhaps improve resulting in a more diversified and even production than today [99–101]. At least the intensity level of farming, from extensive to highly intensive, and industrialization are also very diverse [18]. From an activity mainly artisanal, aquaculture has evolved to include very large companies that export in numerous countries [17, 103]. According to FAO, the annual production by fish farmer also strongly varies from less than 1 ton in Indonesia to 4 tons in India, 7 tons in China, 35 tons in Chile, and 187 tons in Norway [19].
