Fish use their sense of sight, hearing, smell, taste, and touch to gain accurate and up-to-date information about the surrounding environment, which is important to make optimal decisions about possible threats, prey, as well as mates. Due to their aquatic nature fish also have an additional sense, the lateral line or lateralis system. The lateral line is a system unique to aquatic invertebrates, and some aquatic amphibians. Movements of animals in the water cause water displacements and pressure fluctuations, and the lateral line helps makes sense of these hydrodynamic stimuli. In many fish the lateral line can be seen as a line running along the side of the fish. The lateral line is made up of a network of mechanoreceptors called neuromasts, and these sensory structures are typically organized in rows, but they can also occur singly. At its simplest neuromasts occur freestanding on the skin surface (there are holes in the scales for these), however many are embedded in the floor of mucus-filled structures called lateral line canals. Simply, each neuromast is made up of sensory and support cells, where the sensory cells or hair cells bear a hair bundle which send signals via nerve fibers to the brain. Information gathered from the lateral line can be used to detect and avoid prey, communicate between individuals of the same species, school, discriminate between objects, orientate in flowing water, and synchronise to an external rhythm. Fish that feed on insects on the surface of the water sense the surface waves they produce and orient to it using the lateral line system in their heads. Fish in midwater use their lateral line system to discriminate the direction of moving objects, as well as the object’s speed, size, and shape. Blind cavefish can pass through a barrier of rods without touching them, and can build spatial maps, all using information gathered from their lateral lines. In sharks and rays, some of the neuromasts have been modified to become electroreceptors which detect the tiny electric potentials generated by muscle contractions of prey.
Written by: Minke Tolsma
For further reading:
- Bleckmann, H. & Zelick, R. 2009. Lateral line system of fish. Integrative Zoology 4: 13-25.