Fig. 4

Anxiety-related behaviours and whole-body cortisol levels were altered in adult mecp2^−/− fish while locomotion and social preference were unaffected. Locomotion in the open-field (a) was not affected but adult mecp2^−/− fish spend significantly less time in the (b) centre zone in the open field compared to the mecp2^+/+ group and (c) male mecp2^−/− fish showed somewhat less time in the periphery, compared to female mecp2^−/− fish. During the presentation of social stimuli, time spent in the social zone (d) was not significantly different in adult mecp2^−/− (n = 43) as compared to mecp2^+/+ (n = 22). While mecp2^−/− fish generally trended towards more time closer to social stimuli than mecp2^+/+ fish across the 15 min (e) the SPI was not different between the two groups of fish (f). In a novel tank diving task, the mecp2^−/− (n = 22) zebrafish made less bottom-to-middle transitions (g) and spent less time in high-mobility state (h) and more time in the immobile state (i) as compared to mecp2^+/+ (n = 10) indicating an increase in bottom-dwelling and freezing behaviours, but overall time spent in bottom, middle, and top areas (j) was not different between the two genotypes. Baseline cortisol levels (k) were higher in experimentally naïve mecp2^−/− (n = 6) fish compared to mecp2^+/+ (n = 6) zebrafish. *p < 0.05 and ****p < 0.0001. Mean ± SEM