Although this test has restricted predictive value for aggression directed at real rivals , it was specific as a result of, unlike other behavioral tests, it doesn’t have an impact on the concentrations of sex steroid hormones . Body parameters and plasma concentrations of steroid hormones were measured to examine the condition of the fish. The concentrations of estradiol E2 in women and 11 ketotestosterone 11 KT in males were measured to evaluate sexual maturity, and the cortisol awareness was measured to evaluate the strain response after the mirror image test. Measurements of fish body parameters are shown in Fig. 1. 001 for females.