Synchrotron radiation micro-computer tomography (SR mu CT) offers the possibility to investigate biomineralized structures in high detail. Two animals of adult medaka fish (Oryzias latipes) were analyzed by SR mu CT with a resolution of 6.55 mu m: the wild-type animal was normally developed whereas the second animal showed an idiopathic deformation of the cranial and axial skeleton. These deformations could be followed on the macro- and on the microscale (i.e., on the level of the individual ribs and fin bones). Our study clearly demonstrates that SR mu CT is an excellent technique to study alterations in the skeletal structure of fish in detail. (C) 2007 Elsevier Inc. All rights reserved.