Meeting Abstract
Sharks have a multitude of defining evolutionary structures that distinguish them from other clades of fish. One such striking feature is their skin. The entire surface of shark skin is embedded with thousands of placoid scales or dermal denticles. While previous research has shown that denticles vary both around the body of a shark and among species, little has been done to quantify surface roughness and three-dimensional denticle structure. We investigated and quantified differences in scale shape and size on the skin of three individual smooth dogfish (Mustelis canis) using microCT scanning, gel-based surface profilometry, and histology. On each individual, we imaged between 8 and 20 distinct areas on the body and fins, and obtained selective comparative data from leopard, sharpnose, mako, gulper, and great white sharks. We generated 3D images of individual denticles and took measurements of denticle volume, surface area, and crown angle from the microCT scans. Surface profilometry was used to quantify metrology variables such as roughness, skew, kurtosis, and maximum and minimum height of surface features. These measurements confirmed that denticles on different body areas of smooth dogfish varied widely in size, shape, and spacing. Denticles near the snout are smooth and paver-like relative to denticles on the body. Body denticles have between one and three distinct ridges, a diamond-like surface shape, and a dorsoventral gradient in spacing and roughness. We noted considerable variation in denticle structure among regions on the pectoral, dorsal, and caudal fins, including a leading-to-trailing edge gradient in roughness. Surface roughness in smooth dogfish varied around the body from 10 to 70 microns, and all species studied showed a similar range of values.
