Fig. 1. The effects of cortisol and cortisol+RU486 treatments (single dose injections) on the behaviour scores of (A) size-matched (respectively, 14 and 10 pairs) and (B) size-mismatched (respectively, 14 and 10 pairs) pairs of rainbow trout Oncorhynchus mykiss confined together for 5 days. Values are means ± 1 S.E.M.; N values are given in the figure. Means were calculated for each combination of social status and treatment within a treatment group to give dominant treated, subordinate treated, dominant untreated, and subordinate untreated categories. There was no significant effect of treatment group on behaviour score within a category (Student's t-test, P>0.05).