How do clupeiform fish schools form during early development?

Clupeiform fish typically begin to form schools once they reach a length of approximately 10 mm (0.4 inch).12

The process begins when a small fish approaches the tail of another. Both individuals then vibrate their bodies in a series of rapid motions, after which they begin to swim together. As additional fish join this initial pair and the individuals grow slightly larger, these small groups increase in size and begin to exhibit a steady, organized schooling pattern.1

This instinctive tendency to associate is vital for survival, as it provides protection from predation. While the exact mechanisms are still debated, it is believed that schools may maintain their cohesion through visual contact or via sensations received by the lateral line system—a series of sensory endings along the side of the fish that detects disturbances in the surrounding water.13