Résumé
Behavioural syndrome, which refers to a suite of correlated behaviours across differing situations, has been identified in numerous animals, including fish. The presence and conservation of a behavioural syndrome throughout evolutionary times suggests it confers various advantages at a population level. In eels, such as the European eel (Anguilla anguilla), activity and aggressiveness are important factors in their life history, since both traits influence dispersal and territoriality. In the present study we investigated whether these behavioural traits were consistent at both the nychtemeral scale (24 h) and over a long time period (7 months). In addition, we investigated if aggressiveness and activity were positively correlated. Both activity and aggressiveness were significantly repeatable, indicating that both behavioural traits could be considered as personality traits. Interestingly, nocturnal activity was correlated to diurnal activity, indicating that this personality trait was highly stable at the circadian scale. Both aggressiveness and activity were correlated in the course of the experiment, underlining the presence of a behavioural syndrome. The detection of two behaviourally distinct groups in juvenile eels: aggressive and active individuals versus their counterpart have implications in the understanding of the colonization profile of the watershed. We discuss these findings in relation to the ecology of this species.