**7. Personality**

The concept of behavioural syndrome (synonyms = personality, temperament, behavioural differences) is defined as a collection of behavioural traits, which are constant over time and environmental situations [80]. It does not mean that these traits do not evolve with time for example, but that the combination of them is constant. This concept has been widely used in fishes. These behavioural syndromes may be dependent from the environmental situations (i.e. high or low density) and have different performances (i.e. boldness or shyness are the most efficient). This concept has been used for cultured fishes (*Salmonidae*) in order to select the most advantageous behavioural traits for the rearing of fishes in captivity. The human selection on economic criteria (size, growth) may be biased and this selection leads to keep the individuals that have the highest boldness (as in *Salmonidae*). But these results are not so clear, and in some cases, the selection of the individuals, which have the highest boldness, leads also to the selection of the most aggressive animals, i.e. salmon reared in farm for many generations are more aggressive and bold than individuals hatched in farm but from wild parents [72, 81]. Now, it is possible by comparing wild and domesticated strains, to show the existence of QTL for personality trait such as boldness. By testing the boldness of Zebra fish (*Danio rerio*), Wright et al. [54] showed that there are strong behavioural differences between a wild-derived strain of fish and a laboratory strain AB. Based on anti-predator behaviour, their results indicated a QTL for boldness on chromosomes 9 and 16 and suggest another genomic region that influences anti-predator behaviour on chromosome 21. So, these results confirm the possibility of QTL mapping of behavioural traits in zebra fish and the consequences of selection during domestication.

These behavioural differences between captive of reared fish and their wild conspecifics could be used in the frame recovery programmes for threatened and endangered species. By comparing the boldness and prey acquisition behaviours of wild bull trout (*Salvelinus confluentus*) and reared ones, Brignon et al. [82] showed that wild fish and captive reared fish from complex habitats exhibited a greater level of boldness and prey acquisition ability, than fish reared in conventional captive environments. These results suggested that rearing fish in more complex captive environments could create a more wild-like phenotype than conventional rearing practices.

In this frame of animal personality, or coping style, an important effect of the domestication is the reduction of emotional reactivity or responsiveness to a fear-evoking stimulus [83]; the emotional reactivity of wild fishes is better than those of reared individuals [84]. The emotional reactivity of an animal is necessary for provoking a flight response when there is a potential danger; it could be linked to a survival response. It seems that after domestication, fishes lost very rapidly, in only one generation, the stress response. This change in behaviour is probably directly linked to physiological changes: in the rainbow trout, two different lineages were selected on the basis of their rate of cortisol as responsiveness to stress. Individuals, which showed a low rate of cortisol, had a lower response to stress; they developed a better foraging behaviour but had a bad response to a potential danger. These individuals were well adapted to the environmental conditions of fish farms, but not the natural environment [85]. This is a general problem; the selection by humans of particular lineages of fishes based on their potentiality of growth and development has an influence on other life traits especially on behavioural traits. In the sea bass, the repetitive application of stress elements (pursuit of the fishes with a net, luminous changes, application of predator lure) modifies the foraging habits of wild fishes but also of reared ones. This could be interpreted as a habituation to the situation, which becomes less stressful [86].
