What is the Lateral Line?
The lateral line is a tube running just below the surface of the skin along the sides of the body, usually marked externally by a series of pores that open out through the scales. View these fish anatomy diagrams from the Badman's Tropical Fish website to get an idea of where the lateral line is located. Even though these diagrams are of freshwater fishes, the lateral line relates in the same way to all fish species. It is a very important sensory organ. It can detect minute electrical currents in the aquarium water and also functions as a kind of echo location system that helps fish to identify their surroundings. There is usually only a single lateral line on each side of the body, but many variants of the typical lateral line may occur. For example, on the sides of the Belonidae (Needle Fish), Hemiramphidae (Half-Beak Fish), Exocoetidae (Flying Fish), and a few other fish families, the lateral line runs very low on the sides. On some species the lateral line may also be incomplete, in which case it stops short of the base of the caudal fin. It may also be interrupted, meaning that it ends and then recommences after a gap, perhaps several scale rows lower down on the body, as in some of the Labridae (Wrasse) species. Strangely enough, in a fairly large number of families the lateral line is absent altogether.