Lordosis in fish is an abnormal ventral curvature of the vertebral column, accompanied by abnormal calcification of the afflicted
vertebrae. Incidences of lordosis are a major problem in aquaculture and often correlate with increased swimming activity. To
understand the biomechanical causes and consequences of lordosis, we mapped the morphological changes that occur in the
vertebrae of European sea bass during their development from larva to juvenile. Our micro-CT analysis of lordotic and non-lordotic
vertebrae revealed significant differences in their micro-architecture. Lordotic vertebrae have a larger bone volume, flattened dorsal
zygapophyses and extra lateral ridges. They also have a larger second moment of area (both lateral and dorso-ventral) than nonlordotic
vertebrae. This morphology suggests lordotic vertebrae to be adapted to an increased bending moment, caused by the axial
musculature during increased swimming activity. We hypothesize the increase in swimming activity to have a two-fold effect in
animals that become lordotic. The first effect is buckling failure of the axial skeleton due to an increased compressive load. The
second effect is extra bone deposition as an adaptive response of the vertebrae at the cellular level, caused by an increased strain and
strain rate in these vertebrae. Lordosis thus comprises both a buckling failure of the vertebral column and a molecular response that
adapts the lordotic vertebrae to a new loading regime.