## Similar protocols

## Protocol publication

[…] Two experimental treatments (i.e., size-matched predators and larger predators) and a control treatment (size-matched conspecifics) were videorecorded during the experiment (). Black carp with a similar body size (body mass: 2.61 ± 0.10 g, standard body length: 5.55 ± 0.06 cm, N = 28) were randomly assigned among three experimental groups, and snakehead with two different body sizes (body mass: 2.57 ± 0.12 g, standard body length: 5.86 ± 0.12cm, N = 6; body mass: 7.01 ± 0.22 g, standard body length: 7.88 ± 0.15 cm, N = 6) were assigned to either the size-matched predator treatment or larger predator treatment. In the control treatment, a black carp was individually transferred to the central arena of the experimental setup and videorecorded (15 frames per second) for 1 h. Then, another black carp was transferred to the ring area and videorecorded for another hour (N = 8). In the experimental treatments (i.e., the size-matched predator treatment and large predator treatment), the procedure was the same as for the control treatment, except that a snakehead was placed in the ring area instead of a black carp (N = 6).The videos were converted from .wmv to .avi format with Format Factory (http://format-factory.softonic.cn). Then, the centroid-based trajectories of the fish and the coordinates of each frame with the range of 10 min before and 10 min after introduction of another fish were obtained using **idTracker** (). The relative size between the pixels and entities was used to calculate the real coordinates of the experimental fish. The parameters for describing spontaneous activities and their interactions were calculated with the formulas listed below.Distance (cm) between centroids of two fish: (1)Dt=x1t−x2t2+y1t−y2t2where x(t) and y(t) are the coordinates of the centroid position of two fish in the horizontal plane at time t.Spontaneous swimming speed while moving (cm s−1): (2)vt=xt−xt−12+yt−yt−12∕dtwhere x(t) and y(t) are the coordinates of the centroid position of either prey or predator in the horizontal plane at time t, x(t − 1) and y(t − 1) are the coordinates in the previous frame, and dt is the time interval between successive frames (one-fifteenth, i.e., 0.067 s). Fish were defined as moving when the values were higher than 1.75 cm s−1.Percent time moving (%) of individual fish: (3)Percenttimemoving=T2T1×100%where T1 is the duration of observation and T2 is the time spent moving (i.e., swimming speed higher than 1.75 cm s−1).Total distance moved (cm) was the product of swimming speed and percentage time of movement. [...] **SPSS** Statistics 17 (IBM, Armonk, NY, USA) was used for data analysis. All values are presented as the means ± SE, and P < 0.05 was considered statistically significant. The difference in the distance between the two fish among the control and two treatments was assessed using one-way analysis of variance (ANOVA). The effects of experimental treatments (control, size-matched and large predator) and predator exposure (before and after introduction of a companion) were tested by linear mixed model analysis with fish ID as random factor. A Duncan test or paired t-test was performed if a statistical assessment of the difference among three treatment groups or between those with or without a companion was necessary. All data were tested for normality by One-Sample Kolmogorov–Smirnov Test. […]

## Pipeline specifications

Software tools | idTracker, SPSS |
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Applications | Miscellaneous, Macroscope & basic digital camera imaging |

Organisms | Mylopharyngodon piceus, Channa argus |