Fish inner ear otoliths stop calcium incorporation after vestibular nerve transection

Previous investigations revealed that the growth of fish inner ear otoliths (otolith size and calcium incorporation) depends on the amplitude and the direction of gravity, suggesting the existence of a (negative) feedback mechanism. In a search for the regulating unit, the vestibular nerve was unilaterally transected in neonatal swordtail fish (Xiphophorus helleri) which were subsequently incubated in the calcium-tracer alizarin-complexone. Calcium incorporation and thus otolith growth ceased on the operated head sides, indicating that the brain is significantly involved in regulating otolith growth.