Statistics
All behavioral, electrical, and hormonal data were analyzed with non-parametric tests: Wilcoxon Matched-Pairs test (paired variables in the same fish), Mann–Whitney U test (independent variables using sets of data from different fish). For this reason, data are expressed as median ± median absolute deviation (MAD) throughout. We used Chi-square tests (χ2) to test the effect of FAD administration and castration on contest outcome. In χ2 test, the null hypothesis was that larger fish would win the contest, while the alternative hypothesis was that larger fish would not win the contest (including not only contests
won by the smaller fish but also unresolved contests).