Fig. 4. Effects of multiple steroids on maximum contractile force developed by ventricle strips from rainbow trout at 0.5 Hz. Ventricle strips from both male (A) and female (B) rainbow trout were treated with 11-ketotestosterone (11KT; 0.3 µmol l^–1), testosterone (T; 0.3 µmol l^–1), cortisol (C; 0.1 µmol l^–1 in males and 0.01 µmol l^–1 in females), estradiol (E2; 1.0 nmol l^–1) or combinations of two different steroids at the same concentrations. In males, the maximal effects of 11KT+C (178±4%) and T+C (163±3%) were completely additive when compared with their independent effects (11KT, 143±2%; T, 136±5%; C, 132±5%). By contrast, maximal effects of E2 (129±4%) and C (136±4%) were not additive (143±3%). All values are means + S.E.M. (N=9). *P<0.01 compared with strips treated with one steroid hormone.