Fishes have a particular kind of mechanoreceptors, sensitive to mechanical stimuli, pressure waves or pressure differences caused either by the locomotion of the fish itself by a fish passing by or by currents in the ambient water. The basic pattern is a cluster of sensory cells with a kinocilium and a number of stereocilia, covered by a cupola of a stiff mucus and surrounded by supporting cells. They may lie either at the surface of the epidermis, anchored in the corium, as free neuromasts or free sensory hills, or they are sunken in open grooves or furrows as in lower fishes, or, in bony fishes, enclosed in canals which are connected to the ambient water by lateral line pores. The pores need not be open but may be covered by a thin epidermal membrane, as is the case in the mormyridae. The pores, open or covered, form conspicuous lines which are distinctive features in the sytematics of fishes, at least the higher taxa. Most obvious often is a row of scales along the trunk and tail of a fish which each are enclose a short canal and a pore: the lateral line scales which gave the name to this sensory system. The lateral line organs are not confined to the trunk and tail, they also are abundant on the head, where they are aligned in distinctive rows of pores. In mormyridae, however, on the head the lateral line canals are hidden beneath the electroreceptor epidermis and deeply sunken into the bones, but still there are sensory organs, neuromasts, in these canals but no openings to the outside. The canals are followed by blind ending tubes which come close to the surface on the neck and below the pectoral fins, 'nuchal' and 'gular' canals. They seem to receive pressure changes of the ambient water and to conduct such kind of 'pressure waves' to the sensory organs in the respective canal. Mormyridae do have canal neuromasts as well as free neuromasts along the back and the belly, innervated by the nervus lateralis posterior, and also free neuromasts in several rows on the head, innervated by the n. lateralis anterior. In the genus Stomatorhinus the lateral line does not reach down to the caudal peduncle.

Alternative form for lateral line organs : neuromasts.