Lateral line: the sensory system that lets fish feel water movement

Structure and components

Externally the lateral line is often visible as faint pores or grooves running lengthwise from the head toward the tail, typically from the gill covers to the caudal peduncle. Internally it is formed from modified epithelial cells, commonly called hair cells, that are topped by a gelatinous cupula. When water moves past the skin these structures bend and the hair cells transduce mechanical deflections into electrical signals that are sent to the brain. The epithelial receptors are sometimes collectively described as modified epithelial cells and they turn mechanical input into neural impulses.

How it works

Hair cells in the lateral line respond to low-frequency flow, pulses and vibration (vibration) rather than to high-frequency sound. Afferent nerves carry the signals into the animal's central nervous system, where they are integrated with other senses. The system can detect the direction and relative strength of currents and can sense disturbances such as the vortices shed by moving bodies; for example, a predator may follow the trail of vortices produced by fleeing prey (vortices).

Functions and behavior

The lateral line contributes to a range of behaviors. It helps fishes maintain position in a school (schooling), navigate complex environments, detect approaching predators or prey, and orient relative to obstacles and substrate. In some species the lateral line's receptor organs are modified into electroreceptors, allowing detection of weak electrical fields as an additional sensory modality.

Distribution, development and related systems

The lateral line is widespread among bony fishes and cartilaginous fishes, and a lateral-line-like system occurs in most amphibian larvae and in some fully aquatic adult amphibians (amphibian). Terrestrial vertebrates lack an operational lateral line because it functions only in an aquatic medium. During development the lateral line arises from placode-derived cell clusters that migrate and differentiate into the arranged receptors and canals seen in adults.

Importance and applications

Beyond its biological role, the lateral line has inspired technological designs in underwater robotics and flow sensors. Engineers mimic the array of hair-cell-like detectors to build arrays capable of detecting flow direction and disturbances for navigation and object detection. For further reading on anatomy, physiology and engineering applications, see these resources: overview, mechanisms, cell structure, signal transduction, neural pathways, behavioral studies, hydrodynamics, external morphology, comparative systems, developmental biology.