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

The behavioural patterns of juvenile white-seabream suggest that asymmetry in residence is an important factor governing the outcome of contest betwee n individuals of this species. Asymmetries due to resident status had stron g effects on agonistic behaviour, with asymmetries in body sizes producing weaker effects. Resident fish won all the combats against intruders of lowe r or similar length. However, when the intruder was larger than the residen ts (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 correlatio n between fight intensity and size asymmetry in favour of the resident fish . The resident fish was more aggressive and persistent in attacks, and cont ests were more intense when the size of the intruder was greater. During ag onistic interactions, the frontal attacks and lateral displays were more fr equent 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. (C) 1999 Wiley-Liss, Inc.