Effects Of Hexabromocyclododecane On Nervous System And Movement Ability Of Oryzias Melastigma Larvae

HBCD (hexabromocyclododecane) is one of the most widely used additive brominated flame retardants (BFRs) in the world just less than TBBPA and PBDE. It’s well known as a persistent organic pollutant (POP) that can accumulate in the environment and transfer though the food web. HBCD has been detected in organisms and concerned to be a toxic substance that should elimited in the near future. Marine medaka (Oryzias melastigma) is a new and useful seawater fish model for ecotoxicological studies. In the present work, blastula stage embryos of O. melastigma were exposed to HBCD at environmental concentrations (0,0.2,2,20nM) for15days. The effects in nervous system and movement ability of larvae were focused.The results showed that HBCD increased the mortality. The hatching rates were decreased in a dose-dependent manner. HBCD increased the heart rate after expousure for6and13days. The heart rate in larvae was higher than in embryos.HBCD reduced the locomotion of medaka larvae showed as the reduction of total swimming distance and average speed in free condition. Startle response was impressed and resulted in the decline distance after mechanical touch in HBCD exposure groups. Those changes may due to the abnormal energy suppliment and ion balance in marine medaka which is involved with the activity of ATPases. ACh and the activity of ChAT and AChE in larvae was increased. Compared to the control, GAP-43and AIMP1expressed in brain were reduced especially in hindbrain where was supposed to play a key role in regulation of fish movement. TUNEL showed the increase of apoptosis cells in the brain of larvae. HBCD also impairs the development of neuromasts in lateral line system. The effects in nervous system and the sensory system may explain the movement disorder of medaka larvae exposed to HBCD. We tested the expression of genes involve with nervous system and movement by real-time PCR, the outcome doesn’t show the same trend with the result of microarray in every gene. In conclusion, HBCD has neurotoxcity to embryos of marine medaka. The damage in nervous may cause the disorder of larvae movement. We suggest the effect level of HBCD in marine medaka embryo is0.2nM. The mechanism of HBCD need further studies.