Cognitive performance
In the observer trials, 55 of 60 pairs established clear dominant/subordinate relationships within the five-hour period. Considering time differences between observer and naïve trials (i.e. observer trial time minus naïve trial time), trout raised in complex habitats showed greater improvement in time needed to establish a stable hierarchy in the observer trial than did those from simple habitats (F 1,98 = 13.09, < 0.001). Females generally showed less improvement than did males in the observer trials over the naïve trials (F 1,98 = 4.57, p  = 0.034), especially those from the simple habitat; but, females from the complex habitat showed greater improvement than did males (sex/habitat interaction:F 1,98 = 11.41, = 0.001) (Fig. 5A). Greater brain mass was also associated with quicker times in the observer trial (F 1,42 = 6.93, p  = 0.011) (Fig. 5B), but no specific brain region exerted a significant effect on time differences between trials (telencephalon:F 1,42 = 1.87, p  = 0.179; optic tectum:F 1,42 = 0.24, p  = 0.627; cerebellum:F 1,42 = 0.05, p  = 0.828; olfactory bulb:F 1,42 = 0.88, p  = 0.353).