Whole-body cortisol concentrations and ontogeny of aggressive behavior in yellowtail (Seriola quinqueradiata Temminck & Schlegel; Carangidae)

Abstract

Ontogenetic changes in whole-body immunoreactive cortisol concentrations (IRC) and aggressive behavior were examined in yellowtail Seriola quinqueradiata (Temminck & Schlegel; Carangidae). Baseline IRC significantly increased during the transition from larval to juvenile stage and was correlated with the onset of aggressive behavior. Handled fish (13.1 +/- 2.6 ng/g tissue) showed an IRC level about three times higher than unhandled fish (4.7 +/- 1.4 ng/g tissue), indicating that whole-body immunoreactive cortisol level may be an indicator of stress in juvenile yellowtails. Behaviorally subordinate fish (8.6 +/- 1.6 ng/g tissue, n = 4) showed IRC levels significantly higher than dominant fish (0.6 +/- 0.3 ng/g tissue, n = 4). Whole-body immunoreactive cortisol levels may thus reflect stress and social status in juvenile yellowtails, and the inverse relationship between social rank and IRC may result from agonistic interactions.