Exposure to cadmium causes inhibition of otolith development and behavioral impairment in zebrafish larvae

Otolith consisting largely of calcium carbonate, fibrous and proteins, is vital for maintaining body balance and/or hearing of fish. The formation of otolith involves Ca 2+ transport and deposition. In the present study, we investigated the effects of Cd 2+ on otoliths development by using zebrafish embryos as model. The results showed that exposure to Cd 2+ inhibited the utricular and saccular otoliths growth, indicated by reduced lateral areas. Swimming speeds were reduced and a losing balance control was observed in Cd 2+ exposed larvae. The genes related to Ca 2+ transport (e.g. plasma membrane Ca 2+ -ATPase isoform 2 , pmca2 ; Ca 2+ -ATPase isoform 2 , atp2b1a ) and regulation (e.g. parathyroid hormone ligand type-1 , pth1 ; stanniocalcin isoform 1 , stc1 ) were significantly downregulated. However, the adverse effects of Cd 2+ on otoliths growth and swimming activity can be protected by supplementation of Ca 2+ in exposure medium. Body burden of Cd 2+ in larvae was reduced upon the supplement with Ca 2+ . The overall results suggest that exposure to Cd 2+ can inhibit influx of Ca 2+ , leading to less deposition of CaCO 3 for otolith growth, and finally result in impaired balance control and swimming activity in zebrafish larvae.