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

Abstract

-The long term influence of individual biological rhythms on group feed demand behaviour was investigated in European sea bass (Dicentrarchus labrax) held under controlled environmental conditions with an on-demand feeding system. The experiment was realized over 219 days with 190 fish distributed on 4 tanks. Sea bass had a mean body mass comprised between 139 g to 183 g. The number of feed demand acts by each individual was calculated daily, and the population could thus be partitioned into three categories (high-, low-and zero-triggering fish). The duration of the period that an individual held high-triggering status could vary, but was 63 ± 16 days on average. The transition period between two highest-triggering fish in one tank was on average 4 ± 4 days. The group feeding rhythm followed the same pattern of feed demand rhythm as the highest-triggering individual fish. When the highest-triggering fish was nocturnal, the totality of feed demand in the group was realized during the night with one peak at 22:00, corresponding to dusk under experimental conditions. When the highest-triggering fish was diurnal, the majority of feed demand in the group was realized during the light period with one peak at 06:00, corresponding to dawn, and/or another at 12:00. This study therefore highlights that sea bass group feeding behaviour is not the sum of individual feed demand behaviours, but is directed by the rhythm and behaviour of a few high-triggering fish. The regular changes of high-triggering fish in the group proved that it was not the identity of these particular fish that was most important for the group, but their role as a feed demand leader. Key words:Feeding rhythms / Feed demand leader / Social interactions / Self-feeder / Dicentrarchus labrax Résumé -L'influence à long terme des rythmes biologiques individuels sur le comportement alimentaire du groupe est étudiée sur des bars européens (Dicentrarchus labrax) maintenus dans des conditions environnementales contrôlées et avec un système d'alimentation à la demande. L'expérience est réalisée sur 219 jours avec 190 poissons répartis dans 4 bassins. Les bars ont un poids corporel moyen compris entre 139 g à 183 g. Le nombre de demande alimentaire réalisée par chaque individu est calculé quotidiennement, et la population a pu être divisée en trois catégories (manipulateur principal, occasionnel et non manipulateur). La durée pendant laquelle un manipulateur principal reste actif peut varier, mais elle est en moyenne de 63 ± 16 jours. La période de transition entre deux manipulateurs principaux dans un bassin est en moyenne de 4 ± 4 jours. Le rythme alimentaire du groupe suit le même patron que celui du manipulateur principal. Lorsque le manipulateur principal est nocturne, la totalité des demandes alimentaires du groupe est réalisée pendant la nuit avec un pic à 22:00, correspondant au crépuscule dans les conditions expérimentales. Lorsque le manipulateur principal est diurne, la majorité des demandes alimentaires du groupe est réalisée pendant la périod...

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

“…This observation is in accordance with what has been found for other species such as sea bass (Millot and Bégout 2009) charr Alanärä andBrännäs 1996, 1997). Even if no agonistic interaction between fish was observed during triggering actuation and food delivery, it is probable that the status of HTF in the group was due to large body size and high social status.…”

“…Trigger actuations were recorded continuously throughout the experimental period and the identity of the triggering fish was determined in approximately 90% of the cases (the remaining 10% without fish ID was not included in the analyses). The number of trigger actuations per individual was used to calculate the proportional contribution of an individual fish to the total number of trigger actuations within its group over the entire experimental period and to assign the individual to one of the categories: high-triggering (< 25% actuations, HTF), low-triggering (> 25%, LTF) and zero-triggering (0%, ZTF) fish (Coves et al 2006;Millot et al 2008;Millot and Bégout 2009).…”

“…Self-feeding devices are widely used to study different aspects of fish behaviour, such as feeding activity (Azzaydi et al 1998), group dynamics (Millot and Bégout 2009), operant learning ability (Nilsson and Torgersen 2010) and food preferences (Aranda et al 2000(Aranda et al , 2001. In food preference tests fish generally have access to two or more self-feeders containing different food types (Sánchez-Vázquez et al 1998;Aranda et al 2000Aranda et al , 2001Montoya et al 2011) and higher triggering rate on one feeder is usually considered as a preference for one food type over the other types.…”

“…However, several studies with different species have found that only one or a few individuals (high triggering fish; HTF) in a group account for the majority of the trigger actuations and these individuals may deviate from the group mean in terms of size, social status, and/or sex. 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).…”

Régime alimentaire de <i>Engraulis encrasicolus</i> (Linneaus, 1758) du littoral de la Côte d’Ivoire

“…Dans le milieu naturel, la disponibilité de la nourriture est l'un des facteurs environnementaux les plus importants qui affecte la survie des animaux (Millot et Bégout, 2009). Les variations naturelles journalières et saisonnières de la disponibilité de nourriture dans le milieu naturel conditionnent le rythme d'activité alimentaire chez les poissons (Sánchez-Vázquez et al, 1994).…”