Behavioral and neurophysiological responses of European sea bass groups reared under food constraint

Abstract

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.

Effect of size grading on sea bass (Dicentrarchus labrax) juvenile self-feeding behaviour, social structure and culture performance

“…According to the feeddemand behaviour classification previously described (Covès et al 2006;Di-Poï et al 2007Millot et al 2008), the present study therefore confirmed that within a group of 60-100 sea bass juveniles, only a few individuals were responsible for the majority of food demands, whereas the rest of the population exhibited low-or zero-triggering activity. It also showed, however, that high-triggering fish appeared only after size grading.…”

“…Self-feeders are particularly useful for the study of feeding behaviour in fish (Boujard et al 1992) and, when coupled with a PIT tag detection antenna, have contributed to a better understanding of individual behaviour within fish groups Brännäs 1993, 1996;Brännäs and Alanärä 1993;Covès et al 1998;Rubio et al 2004;Covès et al 2006). This combination of techniques was successfully used in European sea bass, a commercially important species in the Mediterranean (Covès et al 1998;Covès et al 2006;Di-Poï et al 2007;Millot et al 2008. Several authors have shown that, within a group of 50 juvenile sea bass, only a few individuals defined as high-triggering fish were responsible for the majority of food demands in the group, whereas the rest of the population exhibited the defined low-or zerotriggering activity (Covès et al 2006;Di-Poï et al 2007;Millot et al 2008).…”

“…This combination of techniques was successfully used in European sea bass, a commercially important species in the Mediterranean (Covès et al 1998;Covès et al 2006;Di-Poï et al 2007;Millot et al 2008. Several authors have shown that, within a group of 50 juvenile sea bass, only a few individuals defined as high-triggering fish were responsible for the majority of food demands in the group, whereas the rest of the population exhibited the defined low-or zerotriggering activity (Covès et al 2006;Di-Poï et al 2007;Millot et al 2008). Lastly, self-feeding systems are also very promising for fish farming because they can improve growth and feed conversion ratios , they are an attractive alternative to either hand-feeding or automated feeding systems due to their low labour costs (Aloisi 1994), and offer a response to the new concerns about animal welfare, even though their commercial development has been rather limited.…”

Individual fish rhythm directs group feeding: a case study with sea bass juveniles (Dicentrarchus labrax) under self-demand feeding conditions

“…When the transition period between two high-triggering fish was longer, self-feeder activation and food wastage significantly increased (Millot et al 2008). Chen et al (2002) suggested that rainbow trout, Oncorhynchus mykiss (Walbaum) social status was determined by their capacity to use the self-feeder, and this capacity could also determine the individual social status within the group in sea bass (Di-Poï et al 2007). However, changes of the hightriggering fish of a group in our experiment could appear either after fish manipulation (measuring days), which were a potential source of stress, or spontaneously.…”

Evaluation of self-feeders as a tool to study diet preferences in groups of Atlantic cod (Gadus morhua)

“…In rainbow trout (Oncorhynchus mykiss), Arctic charr (Salvelinus alpinus) and sea bass (Dicentrarchus labrax) there is a good correlation between the social rank and the number of self-feeder actuations: one or two dominant fish performed the majority of actuations (Alanärä andBrännäs 1993, 1996;Alanärä 1993, 1994;Millot et al 2008;Millot and Bégout 2009). In Arctic charr and sea bass there is a strong negative correlation between feeding demand (and/or growth rate) and brain serotonergic activity; the main neurological marker of chronic social stress in fish (Alanärä et al 1998;Di-Poï et al 2007). Thus, the assumption that the HTFs are representative of the population may not be true.…”