Conclusions
Studies on non-breeding territorial aggression in birds and mammals have provided a deeper understanding of the underlying regulation of aggression. Here we used an advantageous teleost model to approach this complex behavior and found that high levels of aggression occur in the non-breeding season despite lowcirculating androgen levels. Acute FAD treatment decreased aggression in the nonbreeding seasonwhereas castration had no effect. In all, our results suggest,for the first time in teleost fish, that territorial aggression of G. omarorum during non-breeding season depends on non-gonadal steroids,and that aromatase plays a key role. Our results concurwith studies in birds and mammals and set the stage for future comparative studies which could provide insight into general principles in the control of aggression.