Morphological Characterization and Hydrodynamic Behavior of Shortfin Mako Shark (Isurus oxyrinchus) Dorsal Fin Denticles

Abstract

The shortfin mako shark (Isurus oxyrinchus) is one of the fastest marine fishes, reaching speeds of up to 70 km·h−1. Their speed is related to the skin surface design composed of dermal denticles. Denticles vary in size and shape according to placement on the body and minimize turbulence around the body. The objective of this study is to analyze the interaction between seawater flow and denticles on the dorsal fin. High-resolution microscopy (scanning electron microscopy and confocal microscopy) were used to measure defined parts of the dermal denticles. These measurements, along with ratios based on length-to-width define three morphologies (rounded, semi-rounded, long) that were 3D reconstructed. Computational fluid dynamics simulated fluid passage over reconstructed denticles and describe hydrodynamic efficiency under different conditions. An increase in angle of inclination produced a relevant increase in the drag coefficient, especially for high velocity inlets. The lowest drag coefficient values were found in long and semi-rounded, followed by rounded morphologies. The hydrodynamic behavior of shark skin demonstrates a relation to the morphological characteristics of dermal denticles on the dorsal fin. It is concluded that the best hydroefficiency relies on the rounded morphology and may serve to design hydrodynamically efficient surfaces or manmade assemblies.