In nature, animal groups often split and reunite, and even separated subgroups may remain in visual contact. Traditional models of collective motion typically assume only local interactions between neighbors, so they do not describe information transfer across physical gaps. This work fills that gap by isolating vision as the sole communication channel between two fish schools. Related preprints on synchronization in quantum oscillators and biological systems appear alongside this work, but this study stands out for being the first to quantitatively link inter-group distance to the phase synchronization of their collective orientations.
The experiment used a square aquarium measuring 100×100×40 cm, divided by two transparent partitions into three compartments: the two outer ones each held a school of 10–20 black neon tetras, while the central compartment was filled with water and had an adjustable width from 0 to 40 cm. The transparent walls ruled out hydrodynamic interactions and physical contact, leaving only the visual channel. Fish motion was recorded by an overhead camera at 50 frames per second, and trajectories were extracted using the idtracker.ai software. For each school, the orientation of the center-of-mass velocity vector was computed, showing bistable switching between two opposite directions along the long side of the compartment. The resulting time series were compared with the analytical solution of a model of two coupled bistable oscillators, whose parameters were fitted by maximum likelihood.
With no visual contact (opaque partition), the orientations of the two schools switched independently, and the phase-difference distribution had two equal peaks: parallel and antiparallel alignment. As the distance between schools decreased, the antiparallel peak was suppressed, and at zero gap only a sharp parallel-synchronization peak remained. The coupling parameter extracted from the data decayed with distance as a stretched exponential with characteristic length 4.9±0.7 cm and exponent 0.44±0.04, indicating slower decay than a simple exponential. The phase order parameter (mean cosine of the phase difference) decreased from 0.8 at zero gap to zero with an opaque wall, closely following the theoretical curve. The mutual information between school orientations, corrected for estimation bias, also quantitatively matched the model prediction at all distances.
This work shows that visual coupling between spatially separated animal groups can be described as coupling between bistable stochastic oscillators, and that the coupling strength decays smoothly with distance rather than cutting off at some radius. This differs from neighboring studies of synchronization in quantum systems, where coupling is usually imposed artificially; here the coupling parameter is extracted from the behavior of living organisms. The result is important for understanding sensory ecology and collective perception: at short distances, fish appear to respond to individuals, while at larger distances they respond to the averaged motion of the distant group.
A natural next step is to test how synchronization depends on school size, illumination, and water turbidity, and to add other sensory channels such as acoustic or chemical. One could also investigate how two coupled groups respond to external stimuli, such as a predator appearing, and how alarm information propagates across the gap. Theoretically, it would be interesting to generalize the model to more groups and asymmetric couplings, which could lead to new collective states.
The results will influence research on collective animal behavior, sensory ecology, and the development of biomimetic robots, where information transfer between groups without physical contact is important.
Conduct experiments varying school size and illumination levels to determine how these factors affect the coupling parameters. Also measure the response time of one school to the turning of the other, to estimate the speed of information transfer across the gap.
In the biology of collective motion, an open question is how animals integrate information from distant conspecifics and switch between local and global perception. This work directly links that question to a measurable coupling parameter and shows that the transition from individual to collective perception can occur gradually with distance.
This section is addressed to the author of the paper and their colleagues. Neighbouring works were found by meaning-based search across our archive, not by word overlap. We do not review: we show the field around the work.
What the work does
The study experimentally demonstrates that two schools of fish separated by a transparent partition synchronize their collective directional switches through visual contact. The authors describe this behavior with a model of two coupled bistable stochastic oscillators, whose parameters are fitted to the data, and show quantitative agreement between the model predictions and the experiment.
Where its strength is
The strength of the work lies in isolating the visual channel and quantitatively linking the distance between groups to the phase synchronization of their collective orientations, offering a simple model that accurately reproduces the data.
Where it could go next
Worth trying
Why this may matter
Understanding how animal groups remain connected across spatial gaps could shed light on the mechanisms of collective behavior and aid in building models for robotics.
Nearby works in our archive
The archive is sparse around this work: the closest review is only 0.54, against a usual 0.64. It looks like few have drilled nearby.
Black neon tetras (Hyphessobrycon herbertaxelrodi) have an average body length of only 2.5 cm, yet in the experiment their schools synchronized over distances up to 40 cm, which is 16 times the length of an individual fish.