Many fish are capable of producing sounds. These are usually low-pitched, grunt like noises produced by grinding together pharyngeal teeth or movement of a muscle layer against the swimbladder. Sounds may be used for orientation and keeping together in a loosely feeding group, for sexual or species recognition, or for warning. The lateral line system consists of bendable nerve endings in a series of mucous-filled canals Vibrations in the water or differential pressure in different parts of the canal cause the fluid to move and distort the nerve endings. Because of it's name, we think of the lateral-line system as being oriented laterally on the fish.
Closer inspection shows cephalisation, however, with multiple branches in the head region.
The lateral line system enables detection of both vibrations in the water and changes in the pressure field set up as the fish swims. Ambush predators of deep water often have the lateral line nerve endings exposed, rather than buried in canals. The lateral line sense is sufficiently directional to enable blinded fish to find and capture prey. A very low concentration, perhaps a single molecule in some cases, is necessary to excite nerve impulses from the olfactory epithelium. Fish have elaborate nostrils and enlarged parts of the brain associated with smell.