FIGURE 2

Social preference behavior is dependent on vision. (A) Scheme of the social preference setup. A custom-made T-shaped arena is divided into two completely separated compartments. The lower arm harbors a group of eight fish representing the social stimulus, whereas a single test fish is placed into the upper, perpendicular arm. A transparent window is the only non-opaque interface between the two compartments. The movement of the test fish within the compartment is recorded from the top using an infrared-sensitive camera and an infrared light source placed beneath. The zone in front of the window is defined as social zone (red box) and used for quantifications. (B) Representative heat maps indicate the test fish’s position in the compartment as a function of the condition. In dark conditions and in presence of a social stimulus (light off, + social stimulus), fish stayed in close proximity to the borders of the compartment. In illuminated conditions and absence of a social stimulus (light on, − social stimulus), fish were freely roaming within the whole compartment. In contrast, in illuminated conditions and presence of a social stimulus (light on, + social stimulus), fish spent a significant amount of time within the social zone. (C) Quantification of the time spent in the social zone revealed that fish spent significantly less time in the social zone in dark conditions (17.1 ± 10.6%) or in illuminated conditions in the absence of a social stimulus (5.3 ± 3.7%) as compared to light on conditions with a social stimulus (59.3 ± 17.9%). (D) Quantification of the distance moved showed that fish swam slightly more in illuminated conditions in the absence of a social stimulus (1804 ± 387 cm) in comparison to dark conditions (1507 ± 313 cm) or illuminated conditions with a social stimulus present (1243 ± 321 cm). (E) Quantification of the velocity revealed that the test fish swam faster in illuminated conditions in the absence of a social stimulus (6 ± 1.3 cm/s) compared to dark conditions (5.1 ± 1 cm/s) or in illuminated conditions in the presence of a social stimulus (4.2 ± 1 cm/s). (F) Quantification of the frequency of the fish entering the social zone showed that the test fish entered the social zone significantly more often in dark conditions (20 ± 8) or in illuminated conditions with a social stimulus present (24 ± 24) compared to illuminated conditions without social stimulus (8 ± 7). Statistics: all data are represented as mean ± SD, one-way ANOVA with Tukey’s multiple comparison test, p < 0.05 (*); 0.01 (**); 0.001 (***) or 0.0001 (****).