MCHENRY, MJ*; VAN NETTEN, SM; Univ. of California, Irvine; Univ. of Groningen: The mechanical design of the superficial neuromast in zebrafish

The superficial neuromast (SN) is a microscopic structure within the lateral line system of fish that is used to detect water flow. The morphology and material properties of these delicate structures are not well understood and it is consequently unclear how they filter mechanical information. Therefore, the present study examined the shape and stiffness of SNs in larval zebrafish (Danio rerio). SNs are composed of a transparent gelatinous matrix that is anchored to the body by 4 to 16 hair cells. Using a novel visualization technique, we found that the cupula maintains a tapered cylindrical shape along its height and that this tapering increases above the tips of the kinocilia of the hair cells. This finger-shaped structure has a diameter of approximately 10 µm at its base, extends about 40 µm from the surface of the body. We calculated the flexural stiffness of SNs from measurements of its deflection when pushed (1 to 100pN) with a carbon fiber. We found the Young�s modulus to range between 1 and 100 Pa, which is a range comparable to that of mucus. The elongated geometry and flexible material of the SN suggest that the SN bends when exposed to the hydrodynamic loads typical of swimming fish. Therefore, the beam dynamics of the SN play an important role in the detection of hydrodynamic signals by the lateral line system.