**5. Conclusion**

**3.7. Manipulation of sex and ploidy: genetic management of domesticated** 

The Eurasian perch displays a sexual dimorphism of growth in favor of females [107, 108]; thus, the production of monosex female populations has rapidly appeared as a solution to reduce growth heterogeneity and increase growth performances. Hence, protocols (hormonal treatment with 17α-methyltestosterone) were developed for the production of homogametic males or neomales (XX) [127], with a sperm quality similar to heterogametic males [128]. Once produced and mature, those neomales were breeded with normal females (XX) allowing the production of 100% females, for which growth improvements were observed after 7 months of rearing in RAS at 23°C [129]. In a complementary study, trials of production of 100% female populations were also realized by gynogenesis using spermatozoa inactivated by UV radiation [130]. However, due to the low survival rates as well as insufficient growth performances,

A second path, triploidization, was also studied in order to produce sterile animals. This path also appeared as very important because Eurasian perch is a species that can start a reproductive cycle before reaching market size. It is possible to capture in natural habitats (ponds) sexually mature females and males as such low weights as 10–20 g, even lower for males. As for other species reared in fish farming (salmonids), protocols based on thermal or pressure

With the development of perch farms (7–8 farms localized in Germany, France, Ireland, and Switzerland) and the increase of production in RAS (estimated between 500 and 800 tons per year), first thinking on the necessity to develop selective breeding programs emerged, mainly to improve growth performances and decrease production costs. Yet, up to now, no true selective breeding programs exist, even though basic genetic knowledge was acquired to develop them. Studies have notably allowed to characterize the genetic variability of wild perch, very often used as founding populations of current farmed stocks [132–133] and stocks of domesticated breeders currently present in perch farms [134]. These studies have demonstrated that the available stocks of domesticated perch in farms were (i) sufficiently genetically variable to allow developing selective genetic programs (lack of consanguinity) and (ii) often genetically distant from the origin populations (Alpine lakes) presumably assumed by fish farmers.

The domestication of a species requires the onset of periods of exchanges between all stakeholders of the sector (**Figure 1**), notably to allow transfer of expertise and co-elaboration of projects based on the identification of priorities and major bottlenecks. Concerning Eurasian perch, very rapidly, the few research laboratories implied in this species cooperated and organized scientific seminars at different scales to allow sharing new knowledge. The meetings organized at the transatlantic level (Canada, USA, and Europe) aimed first at sharing works performed on Eurasian and yellow perch. Some of these events (Namur, 2008; Nancy, 2014) had for main objective exchanges between the socioeconomic stakeholders of the sector (fish

**populations**

146 Animal Domestication

this method is rarely used [129].

chocks were also developed to produce triploid perch [131].

**4. Dissemination and knowledge transfer**

The domestication of Eurasian perch was initially based on local issues (niche market, development of activities and jobs in rural environments). This domestication occurred in a few main steps: (1) socioeconomic analysis of the market, (2) first zootechnical trials and choice of the major rearing system (RAS), and (3) acquisition of in-depth knowledge on the successive stages of the production cycle (control of the reproductive cycle and reproduction, control of the larval rearing, on-growing, and quality of products) (**Figure 1**). It is important to highlight that the first two steps strongly considered the knowledge previously acquired on a close species, the yellow perch. Today, the Eurasian perch is considered at the level 4 of domestication, which means that the entire life cycle is closed in captivity without any wild inputs but no selective breeding programs is applied [142].

Even though the first experimental trials were initiated at the beginning of the 1990s, the first perch farm (SARL Lucas Perches) created within the European Union was located in 2002 as a pilot enterprise. Importantly in Switzerland, a perch farm, Percitech, was created much earlier in 1994. About 20 years later, numerous projects were launched, some with very high expectations (e.g., FjordFresh Holding S/A in Estonia), in numerous European countries; 10 of these enterprises truly developed a commercial activity. Today, most perch farms pursue their activities; only few, mainly in Ireland (country where perch is not consumed), have stopped their activity. The investors that initially believed in this species were not issued from the aquaculture sector and discovered it. Sometimes, it corresponds to industrials that succeeded in other sectors and wants to diversify their activities. This initial distance from the aquaculture sector constitutes one of the reasons of the slow development of perciculture. Learning requires time. Without doubt, the domestication of Eurasian perch was and remained a particular human adventure, where the link between the species and humans is visible at different levels and various forms.

In terms of perspective, one can expect that this young sector will pursue its development first based on current farms, whose economic viability remains to be demonstrated and second in link with the emergence of new projects and expansion of the market toward new consumers. This new development could imply the production of both pikeperch and perch within the same farms. To support this development, it is imperative to reduce production costs, high in RAS, and secure current stocks. The decrease of cost production will require in priority the onset of selective breeding programs and genetic improvements, a standardization and rationalization of rearing protocols (e.g., percid feeds, ration tables, etc.) and a reduction of investment levels for the development of new perch farms. For some, the development of a monoculture of perch in ponds could be the solution because it will allow a strong decrease in production cost. On the security side, it is important to (i) better know pathologies associated with this species, notably virus, among which some might represent a major risk for percids [143] and (ii) specify the effects of the domestication process on rearing performances of this species. As any other domesticated species, biological responses and performances of perch are modified by the domesticating environment specific to the rearing system chosen and associated rearing practices. Thus, preliminary results indicated that reproductive performances [144, 145] and its sensitivity to stress and immune system [146–150] depend on farm conditions. In the future, the domesticating context (**Figure 2**) could strongly vary according to local environment, which could lead fish farmer to choose different rearing systems and to target different markets. Once this main choice realized (context and domesticating direction fixed), secondary choices will define the trajectory of domestication that will result in physiological stage capture in nature, of the dynamic of transition (progressive or sharp) and cultural practices used, practices that could evolve over time with different dynamics. This complexity is reinforced by the fact that a population engaged in a specific domesticating context could change into another context because of a modification in the project, as was the case for perch reared in polyculture ponds, then weaned, and grown in cages or RAS (**Figure 2**). This diversity of directions and domesticating trajectories should lead to different evolutions (behavior, stress physiology, reproduction, etc.) variable from a context to another. These evolutions could even lead fish farmers to reconsider the initial choice of founding populations, given the enormous genetic diversity available in wild populations [4].

**Author details**

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Pascal Fontaine\* and Fabrice Teletchea

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**Figure 2.** Diagram explaining the different domestication frameworks and pressures encountered by Eurasian perch during current farming trials (F: Framework, T: Trajectory, P: Path).
