Search

Identifying the communication channels inside a society of zebrafish could allow scientists to trigger specific behaviors on the animals to tests for instance the effect of a drug or a genetic mutation. We propose a robotic system to integrate the zebrafish shoal in a non-invasive way, in order to be accepted by the animals and influence their behavior. This system is composed of two parts: a mobile robot that can reach speed of 50 cms-1 and acceleration of 2 m/s2 which are typical for the zebrafish and a lure, magnetically coupled with the mobile robot, moving inside an aquarium and directly in contact with the fish. Moreover the robot does not need batteries, getting continuous power supply by brushes used to retrieve the power from conductive plates above and under the robot. This allows us to run long time experiments with multiple robots. The robotic device has been tested with group of fish evolving together in an experimental tank for several hours. This innovative system offers a new approach for social behavior studies of the zebrafish and other species of small fish.

Collective behaviour models can predict behaviours of schools, flocks, herds, etc. However, in many cases, these models make biologically unrealistic assumptions in terms of the sensory capabilities of the organism, which are applied across different species. We explored how sensitive collective behaviour models are to these sensory assumptions. Specifically, we used parameters reflecting the visual coverage and visual acuity that determine the spatial range over which an individual can detect and interact with conspecifics. Using metric and topological collective behaviour models, we compared the classic sensory parameters, typically used to model birds and fish, with a set of realistic sensory parameters obtained through physiological measurements. Compared with the classic sensory assumptions, the realistic assumptions increased perceptual ranges, which led to fewer groups and larger group sizes in all species, and higher polarity values and slightly shorter neighbour distances in the fish species. Overall, classic visual sensory assumptions are not representative of many species showing collective behaviour and constrain unrealistically their perceptual ranges. More importantly, caution must be exercised when empirically testing the predictions of these models in terms of choosing the model species, making realistic predictions, and interpreting the results.

Collective behaviour models can predict behaviours of schools, flocks, herds, etc. However, in many cases, these models make biologically unrealistic assumptions in terms of the sensory capabilities of the organism, which are applied across different species. We explored how sensitive collective behaviour models are to these sensory assumptions. Specifically, we used parameters reflecting the visual coverage and visual acuity that determine the spatial range over which an individual can detect and interact with conspecifics. Using metric and topological collective behaviour models, we compared the classic sensory parameters, typically used to model birds and fish, with a set of realistic sensory parameters obtained through physiological measurements. Compared with the classic sensory assumptions, the realistic assumptions increased perceptual ranges, which led to fewer groups and larger group sizes in all species, and higher polarity values and slightly shorter neighbour distances in the fish species. Overall, classic visual sensory assumptions are not representative of many species showing collective behaviour and constrain unrealistically their perceptual ranges. More importantly, caution must be exercised when empirically testing the predictions of these models in terms of choosing the model species, making realistic predictions, and interpreting the results.

Recent studies show differences in individual motion and shoaling tendency between strains of the same species. Here, we analyse collective motion and response to visual stimuli in two morphologically different strains (TL and AB) of zebrafish. For both strains, we observed 10 groups of 5 and 10 zebrafish swimming freely in a large experimental tank with two identical landmarks (cylinders or discs) for 1 h. We tracked the positions of the fish by an automated tracking method and compute several metrics at the group level. First, the probability of the 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 landmarks. Second, the analysis of landmarks occupancy shows that AB zebrafish are more present in their vicinity than TL ones and that both strains regularly transit from one to the other one with no preference on the long duration. Finally, TL zebrafish show a higher cohesion than AB zebrafish. Thus, environmental heterogeneity and duration of the trials allow to reveal individual and 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.

Recent studies show differences in individual motion and shoaling tendency between strains of the same species. Here, we analyse collective motion and response to visual stimuli in two morphologically different strains (TL and AB) of zebrafish. For both strains, we observed 10 groups of 5 and 10 zebrafish swimming freely in a large experimental tank with two identical landmarks (cylinders or discs) for 1 h. We tracked the positions of the fish by an automated tracking method and compute several metrics at the group level. First, the probability of the 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 landmarks. Second, the analysis of landmarks occupancy shows that AB zebrafish are more present in their vicinity than TL ones and that both strains regularly transit from one to the other one with no preference on the long duration. Finally, TL zebrafish show a higher cohesion than AB zebrafish. Thus, environmental heterogeneity and duration of the trials allow to reveal individual and 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.

Collective motion in fish shoals have been studied for many years. Multiple shoal structures and configurations have been observed and indexed since the early 20th century. In the last decades, the development of tracking techniques allowed precise measurements of the shoal dynamics. Nevertheless, most of the studies based on those measurements mainly focus on few configurations (usually an organized and mobile configuration named school and a disorganized and static one named swarm) and do not integrate the variety of structures a shoal can adopt. Moreover, their discrimination methods for these configurations are not adapt to an accurate study of the alternation dynamics between these.Fish shoals take many advantage of the heterogeneities found in their environment (shelters, visual cues, meeting points. ). These heterogeneities can largely influence the shoal dynamics. Among these, the floating objects are the most studied due to economic issues related to the use of FADs (fish aggregating devices) in fishery. Nevertheless, only sparse data are collected in the field as many technical challenges has to be be tackled. The lack of precise measurements makes difficult to study the shoal dynamics under and around floating objects. Similar mechanisms can underlie the floating objects association of many fish species. Furthermore, small species in laboratory experiments associate with floating objects as well. This thesis presents a study of the influence of the floating objects and the population size on the shoal dynamics. In this way, a set of laboratory experiments has been conducted on zebrafish (Danio rerio) varying the number of individuals (from 5 to 25) and the number of floating objects (from 0 to 2). A tracking technique has been developed to detect the fishes under the objects and rebuild fish trajectories when one fish hides others. A thorough analysis of shoal measurements (alignment, speed, ) allowed to establish a discrimination methodology of multiple shoal configurations (a total of seven) and to measure their frequencies and durations. Several configurations are less frequent than the school and the swarm that are the most observed. All the configurations are allocated to either a dynamic state (corresponding to a shoal displacement) or a static state. This division of the dynamics in two states allowed to investigate the influence of the different conditions on the lifetimes of the states and their alternation. Different factors influence the dynamics of the shoal states: the shoal size, the time and the floating objects.Regarding the shoal size, our results show that population size greatly influences the durations of the shoal states. The most populated shoals stay longer in every state and the fraction of time spent in the static state increases with population. Regarding the time, remarkably, the static and dynamic states' duration respectively increases and decreases over time so that the total duration of two successive events (a static state followed by a dynamic state, or vice versa) does not vary over time. Furthermore, during the dynamic state, the shoal speed decreases over time. We also observed that the individuals adopt a preferential direction in our circular tank although they often change direction. In the presence of a floating object, individuals tend to interrupt the dynamic state and favour a transition to the static state beneath it. A retention effect of the object is observed only for populated shoals with an increase of it with population. However, in the presence of two floating objects, the lifetime of the static states under the floating object is shorter and we observe a relatively fast alternation of the shoal location between the two objects. Furthermore, few shoal divisions between the two objects are observed. Although they rarely occur, these divisions are as stable in time as a stop of the whole shoal under a unique object. The methodology introduced here allows a precise study of the fish shoal dynamics in different social and environmental conditions. This thesis highlights numerous effects of the population, the floating objects and time on the shoal dynamics. Several new questionings emerge in conclusion and pave the way to multiple research perspectives., Doctorat en Sciences, info:eu-repo/semantics/nonPublished