The small holes on the head of this Northern pike
) contain neuromasts of the lateral line system.
The lateral line system allows the detection of movement, vibration, and pressure gradients in the water surrounding an animal, providing spatial awareness and the ability to navigate in the environment. This plays an essential role in orientation, predatory behavior, defense, and social schooling. A related aspect to social schooling is the hypothesis that schooling confuses the lateral line of predatory fishes. In summary, a single prey fish creates a rather simple acoustic pattern while pressure gradients of many closely swimming (schooling) prey fish will overlap; that creates a complex pattern, and accordingly the predator will be unable to identify the individual fish through lateral line perception.
The lateral line system is necessary to detect vibrations made by prey, and to orient towards the source to begin predatory action. Fish are able to detect movement, produced either by prey or a vibrating metal sphere, and orient themselves toward the source before proceeding to make a predatory strike at it. This behavior persists even in blinded fish, but is greatly diminished when lateral line function was inhibited by CoCl2 application. Cobalt chloride treatment results in the release of cobalt ions, disrupting ionic transport and preventing signal transduction in the lateral lines. These behaviors are dependent specifically on mechanoreceptors located within the canals of the lateral line.
The role mechanoreception plays in schooling behavior was demonstrated in a 1976 study. A school of Pollachius virens was established in a tank and individual fish were removed and subjected to different procedures before their ability to rejoin the school was observed. Fish that were experimentally blinded were able to reintegrate into the school, while fish with severed lateral lines were unable to reintegrate themselves. Therefore, reliance on functional mechanoreception, not vision, is essential for schooling behavior. A study in 2014 suggests that the lateral line system plays an important role in the behavior of Mexican blind cave fish (Astyanax mexicanus).