Fig. 1

Transgenerational effects of selective breeding on mirror fighting. a Representative heatmap images of an aggressive (top part) and non-aggressive (bottom part) zebrafish individual in the mirror-induced aggression (MIA) setup. b Variation in time spent interacting with the mirror of arbitrarily-selected male and female zebrafish from the local breeding colony (F0 fish) during a 5 min MIA assay. c The 10 most aggressive F0 zebrafish spent significantly more time in aggressive display than the 10 least aggressive F0 zebrafish. n = 10/group (d–g). Increased mirror aggression levels of d 1-month-old (n = 85–96) F1 HAZ (high aggression zebrafish) derived from F0 HAZ, e 1-month-old (n = 100/group) F2 HAZ derived from F1 HAZ, f 1-month-old (n = 38–98) F3 HAZ derived from F2 HAZ and g 1-month-old (n = 34–90) F4 HAZ derived from F3 HAZ compared to respective LAZ (low aggression zebrafish). h–k Mirror aggression levels of the most aggressive juvenile HAZ at adulthood (3 months of age) compared to the mirror aggression levels of the least aggressive juvenile LAZ at adulthood. Analysis revealed higher mirror aggression levels of h the most aggressive F1 HAZ at 3 months of age (n = 19–20), i the most aggressive F2 HAZ at 3 months of age (n = 14–20), j the most aggressive F3 HAZ at 3 months of age (n = 17–19) and k the most aggressive F4 HAZ at 3 months of age (n = 15–19) compared to the least aggressive LAZ of the respective generation at 3 months of age. l–n Behaviour of adult F4 high aggression zebrafish (HAZ) and low aggression zebrafish (LAZ) during prolonged mirror exposure. l Time spent interacting with the mirror, m distance travelled and n time spent immobile of HAZ and LAZ exposed to a 1h mirror-induced aggression assay (n = 30/group). Mann-Whitney U test. ***, P < 0.001; **, P < 0.01 and *, P < 0.05 vs. respective LAZ. Data are presented as mean ± SEM. Source data and individual data values are available in Additional file 2