As scales mature, their outer layers form mineralized canals called radii that harbor blood vessels [ 20 Sire J.Y. Quilhac A. Bourguignon J. Allizard F. Evidence for participation of the epidermis in the deposition of superficial layer of scales in zebrafish (Danio rerio): A SEM and TEM study.J. Morphol. 1997; 231: 161-174 ]. A recent study by Rasmussen et al. [ 30 Rasmussen J.P. Vo N.T. Sagasti A. Fish Scales Dictate the Pattern of Adult Skin Innervation and Vascularization.Dev. Cell.