The Lateral Line Facilitates Rapid Responses in Accelerating Fish Schools.

The collective motion of a fish school emerges from communication between its members, yet the sensory mechanisms mediating this communication remain largely unclear. While the visual system is essential for schooling in a diversity of species, the processing of visual stimuli is substantially slower than the mechanosensory lateral-line system. Through experimental manipulation, previous experiments found only modest contributions by the lateral line on time-averaged schooling kinematics, but substantial changes on the network structure of information sharing. To resolve this apparent discrepancy, we combined hydrodynamic modeling with kinematic and network analysis of schools of 60 rummy-nose tetra (Petitella bleheri). These fish exhibit intermittent motion that requires individuals to respond rapidly to their neighbors during periods of acceleration and deceleration to maintain a cohesive school. Through an analysis of the pairwise cross-correlation of speed during accelerations, we found that fish capable of sensing the flow of their neighbors responded with a latency that was one-third less than that of schools of fish with a compromised lateral line. In addition, flow-sensing schools exhibited higher mutual information (MI) and a more efficient and uniform communication network. No differences in response latency or MI were observed during periods of deceleration. These results demonstrate that the lateral line serves not as a redundant channel to vision, but as a fast sensory pathway that tightens temporal coupling between neighbors during the most rapid motion of fish schools.