Oxytocin reduces the frequency of aggressive behaviours in male betta fish (Betta splendens).

The objective of this study was to evaluate the effect of visual isolation and the influence of oxytocin on the aggressive behaviour of male Betta splendens and produce an ethogram for analyses. In the first stage, the fish (n = 6) were kept for 60 days in a recirculation system, maintaining visual contact. After this period, the mirror test was applied. The same procedure was performed with the same individuals after 30 days of visual isolation. Visual isolation did no effect on the aggressive behaviour. Application of oxytocin (2.5 µg/g) for 1 h (twice) in this first stage was also conducted after the mirror test. The effect of exposure to oxytocin was evaluated by applying the mirror test 24 h after the second exposure. The second stage was conducted with another 10 individuals exposed to oxytocin (7.5 µg/g) for 1 h, after which the mirror test was performed. Exposure to oxytocin (2.5 µg/g) did not effect on combat-related behaviours. However, in the second stage influenced all behaviours related to combat and display, with an increase in the frequency of "rest" behaviour. The results indicate that exposure to a neuropeptide at a dose of 7.5 µg/g reduces the frequency of aggressive behaviour of male Betta splendens.