José J. Castro

Dominance structure in small groups of juvenile white-seabream (Diplodus sargus cadenati de la paz, Bauchot and Daget 1974)

Experiments were conducted to investigate the intraspecific aggressive interactions between juveniles of white-seabream (Diplodus sargus cadenati de la Paz, Bauchot and Daget 1974) in relation to dominance hierarchy in small groups. The agonistic interactions between juvenile white-seabream in small groups originated a peck-dominance hierarchy. The dominant (α-fish) generally interacted aggressively and most frequently with the subordinate that was next in line (β-fish) within the dominance hierarchy. This β-fish interacted aggressively more frequently with the γ-fish, and so on. Results demonstrated that fish do not attack subordinates at random. The level of subordination in small groups of juvenile white-seabream was related to body size. Generally, the more aggressive fish manifest a higher growth rate.

Effect of residence and size asymmetries upon the agonistic interactions between juvenile white-seabream (Diplodus Sargus Cadenati de la Paz, Bauchot and Daget, 1974)

The behavioural patterns of juvenile white-seabream suggest that asymmetry in residence is an important factor governing the outcome of contest between individuals of this species. Asymmetries due to resident status had strong effects on agonistic behaviour, with asymmetries in body sizes producing weaker effects. Resident fish won all the combats against intruders of lower or similar length. However, when the intruder was larger than the residents (higher than 5% in length and 20% in weight), the percentage of combats won by the residents decreased to 85.7%. There was a significant correlation between fight intensity and size asymmetry in favour of the resident fish. The resident fish was more aggressive and persistent in attacks, and contests were more intense when the size of the intruder was greater. During agonistic interactions, the frontal attacks and lateral displays were more frequent when the intruders were similar or larger than residents. Attacks to the flanks and chases were more frequent in pairs where the intruders were smaller. Aggr. Behav. 25:297–303, 1999.

The influence of food distribution on the aggressive behaviour of juvenile white‐seabream (Diplodus sargus cadenati de la Paz, Bauchot and Daget, 1974)

Experiments were conducted to investigate the effect of differences in the spatial distribution of food on the aggressive behaviour of juvenile white-seabream, Diplodus sargus cadenati, both in the presence and in the absence of food. The groups of fish receiving spatially fixed food displayed less aggression than those receiving spatially variable food. The period (before, during, or after feeding) during which aggressiveness is measured also has influence in the results. During the prefeeding and postfeeding periods (absence of food), groups that were fed with food spatially fixed displayed less aggression than those that received spatially variable food. However, when food was present there were no differences in the number of aggressive acts carried out by fish groups in both environments. The aggressiveness shown by the groups of fish was always more pronounced during the postfeeding period than during the prefeeding period. The dominant fish was more aggressive when food was spatially fixed, and especially when food was present. Therefore, the subordinates were more aggressive when food was spatially variable and particularly when food was present and during the postfeeding period.