  Recent studies show differences in individual motion and shoaling tendency
between strains of the same species. Here, we analyse the collective motion and
the response to visual stimuli in two morphologically different strains (TL and
AB) of zebrafish. For both strains, we observe 10 groups of 5 and 10 zebrafish
swimming freely in a large experimental tank with two identical attractive
landmarks (cylinders or disks) for one hour. We track the positions of the fish
by an automated tracking method and compute several metrics at the group level.
First, the probability of presence shows that both strains avoid free space and
are more likely to swim in the vicinity of the walls of the tank and the
attractive landmarks. Second, the analysis of landmarks occupancy shows that AB
zebrafish are more present in their vicinity than TL zebrafish and that both
strains regularly transit from one landmark to the other with no preference on
the long duration. Finally, TL zebrafish show a higher cohesion than AB
zebrafish. Thus, landmarks and duration of the repicates allow to reveal
collective behavioural variabilities among different strains of zebrafish.
These results provide a new insight into the need to take into account
individual variability of zebrafish strains for studying collective behaviour.
