In two experiments, a computerized on-demand feeding system coupled with a PIT tag monitoring device was used to continuously record the triggering activity by ca. 50 individual sea bass for 55 days (Exp. 1, initial average body weight and coefficient of variation, CV: 299 g, 15%) and 69 days (Exp. 2, 157 g, 13%). Each group was stocked in 1 m3 tanks and exposed to a water temperature of 21 ± 1 °C and a light regime of 16:8 LD. Only 5% of the triggering activity was not associated with simultaneous PIT tag detection. Although each individual was detected via PIT tag during the experiment, only 67% and 74% of the fish actuated the trigger at least once in Exp. 1 and Exp. 2, respectively. Moreover, only two fish in Exp. 1 and one fish in Exp. 2 accounted for 82% (43 + 39) and 77% of the total triggering activity, respectively. These three, high-triggering individuals did not exhibit a higher specific growth rate or agonistic behavior as observed by video monitoring. Indeed, zero-triggering fish had either a slightly higher SGR (Exp. 1) or a higher final body weight (Exp. 2) compared with low-and high-triggering fish.

The individual food-demand behavior of juvenile European sea bass (Dicentrarchus labrax, L.) reared in groups under self-feeding conditions was investigated. The triggering activity on self-feeder, i.e. index of the food-demand activity, agonistic interactions and territorial behavior were monitored for periods of 42 to 68 days in six groups of 50 fish. The specific growth rate was calculated and the brain serotonergic activity was used as a stable index of social stress. Inter-individual differences appeared in triggering activity and three groups were distinguished: 3-5 high-triggering fish, 17-30 low-triggering fish and the remaining individuals were null-triggering fish. There were no significant differences in specific growth rates calculated at the end of the experiment (day 42 or day 68) between individuals with high, low, and null food-demand (ANOVA, p>0.05). No territorial or agonistic behaviors were observed, however, there were significant differences in brain serotonergic activity between the three triggering groups (ANOVA, p=0.050 in telencephalon and p=0.004 in cerebellum). Specifically, high-triggering fish had lower serotonergic turnover than low or null-triggering fish. We put forth the hypothesis that fish with low or null-triggering activity could be stressed by the high activity of high-triggering individuals.

Songbird mates change their call structure and intra-pair communication at the nest in response to environmental noise Highlights: Both zebra finch parents incubate and they use coordinated call duets when they meet at the nest. In their natural habitat, birds face variable wind noise that may constrain their communication at the nest. In response to an experimental noise, pairs adjusted their duets and increased their effort to communicate. Duets' flexibility in response to noise depended on the context of meeting at the nest. Males and females produced louder calls with an up-shifted frequency spectrum in response to experimental noise.

In self-feeding conditions, a few individual sea bass ( Dicentrarchus labrax (L., 1758)) display strong activity in striking the food dispenser, whereas the remaining individuals of the group actuate the feeder weakly or never. Here, we investigated the effects of removal of the individuals showing dominant activity on the social and feeding behaviours in groups of juvenile sea bass. Following removal, new fish showing a dominant self-feeding activity quickly appear. They always come from the group of fish that have a low number of triggering actuations. This observation shows that it takes less time, about 5 days after the removal of dominant triggerers vs. 14 days at the beginning, for the re-establishment of the behavioural structure, suggesting the possibility of social transmission between individuals. The fish that show weak triggering activity seem to reach the high-food triggering level without obvious signs of competition. This experiment reveals the importance of the food-demand behavioural structure: the fish displaying the highest activity lead to a general food distribution and play a dominant role in feeding the entire group. Functional plasticity in this role within individuals is also demonstrated, indicating that the high-triggering function is essential for the group and not for the individual themselves.