Document Type



Virginia Institute of Marine Science

Publication Date



Special report in applied marine science and ocean engineering ; no. 272.


The energetics of fish locomotion depends on a balance between thrust and drag. The interest stimulated by "Gray's Paradox", that is the seeming lack of sufficient power to overcome many of the estimated values of drag, has resulted in the delineation of a number of potential drag reducing mechanisms (Webb, 1975). Of particular interest is a variety of structural mechanisms, such as scombroid scale corselets (Walters, 1962) and scale ctenii (Burdak, 1969; Bone, 1972), which increase surface roughness and thereby alter boundary layer characteristics. Elasmobranch placoid scales, or dermal denticles, may perform such a function. Bone and Howarth (1966) have suggested that this type of scale reduces drag by creating turbulence in the boundary layer, thereby preventing its separation. More recently, Walsh and Weinstein (1978) have shown that surfaces composed of longitudinally arranged v-shaped grooves can significantly reduce drag through a reduction in the turbulent bursting activity. Placoid scales from a number of galeoid shark species exhibit this type of surface morphology and may therefore represent a potential drag reduction mechanism. More....



Scales -- fishes, Scales--morphology, Sharks--locomotion