【Reading】そくせん

【English Name】Lateral Line

The sensory organ that runs in a single line down each of the left and right sides of the fish body is the lateral line (sokusen). It possesses the ability to keenly perceive not only changes in water pressure and water flow but also the surrounding electric field.

In many fish, only one pair is found on the left and right, but some species have two or more pairs. On the surface of the lateral line, dedicated scales called "lateral-line scales" (sokusen-rin) are arrayed, and the arrangement pattern of the minute pores opened in them makes it possible to distinguish fish species.

For sushi artisans, the way this line runs holds practical significance. Because the flesh quality differs across the lateral line as a boundary, it relates to how the knife is inserted and the direction of plating. Furthermore, in assessing freshness as well, not a few artisans make their judgment using the condition around the lateral line as a clue.

Sensory organs of similar function are also found on the bodies of crustaceans (shrimp, crab, etc.) and cephalopods (squid, octopus, etc.). Also, the hair cells that support hearing and the sense of balance in the human inner ear are said to be, when traced evolutionarily, structures that differentiated from the lateral-line organ.