Meeting Abstract
Northern clingfish have a remarkable ability to stick to smooth and rough surfaces. Specimens longer than 10 cm can attach to surfaces as rough as 2-4 mm grain size, which is considerably rougher than the roughest ready made sandpaper. These small fish stick with higher tenacity to many rough surfaces than smooth ones. The margin of the suction disc of Northern clingfish is covered with hierarchical structures; papillae (~150µm) that are covered with rods (~5µm), which themselves are divided into small filaments at their tips (~0.2µm). We assumed that these structures on the disc margin in combination with the elastic properties of the suction disc enable adaptation to the irregularities of the substrate surface and by this cause higher friction of the disc margin on rough surfaces. We tested this by measuring friction of the isolated margin of the suction disc using a tilting table. There is a higher friction coefficient on rougher surfaces than on smooth ones. Moreover, we measured attachment forces/tenacity of clingfish using a mechanical testing machine. Applying a paired design, we measured the complete suction disc first then repeated the measurement after removing part of the disc margin. On surfaces over a roughness threshold of 78µm (grain size) the suction disc usually totally failed. Interestingly, removing parts of the disc margin had a minimal effect on attachment to smooth and slightly rough surfaces (35µm grain size). On the latter the tenacity just marginally decreased. The disc margin is not essential for clinging to the smoother substrates where friction is lower.
