We combined behavioral and physiological measures to compare coping style in wild-type Betta splendens and a domesticated strain selectively bred for sports fighting. We showed previously that the fighterstrain is more aggressive than the wild type during experimental conditions that most closely resemble an actual fight.We predicted that compared to the wild type, the fighter strain would show a more proactive coping style, characterizedbylesser cortisol and greater sympathetic responses to non-social challenges. We introduced males to an unfamiliar environment and spatial confinement as challenges that may resemble some of those that B. splendens may encounter in its natural habitat. We developed a non-invasive stress assay that enables repeated individual measures of water-borne cortisol.Weestimated sympathetic activation through opercular beat rate and recorded the duration of behavioral immobility.Wefound that exposure to an unfamiliar environment raised cortisol levels in the wild type but not in the fighter strain andthatconfinement raised cortisol levels in both. In both strains opercular beat rates were significantly reduced during the latter stages of confinement compared to during the early stages. The fighter strain, but not the wild type, adopteda behavioral strategy of immobility from the very beginning of confinement. © 2007 Elsevier Inc.