Effects Of Salinity Change On The Development Toxicity Of Marine Medaka Embryo Induced By Crude Oil Exposure

The slick oil of oil spill accidents could diffuse to the estuary areas with fluctuated salinity under the effect of waves.Salinity change may greatly affect the toxic effects of fish organisms induced by oil pollution.However,there were rare researches focusing on the toxic effects of fish organisms induced by oil pollution with salinity change.Therefore,this study selected a typical oil——Oman crude oil as the test oil and an emerging marine model fish species——marine medaka(Oryzias melastigma)as the test organism to perform subacute toxicity exposure for 18 days.To explored the development toxicity and its impact mechanisms of marine medaka induced by crude oil Water-Accommodated Fractions(WAFs)at 8 diluted concentrations with 0.5 ‰,15 ‰ and 30 ‰ salinity.The lethal,hatching,sublethal toxicity endpoints,antioxidant enzyme activity,functional gene expression and petroleum hydrocarbon content were observed,determined and analyzed from the individual,physiological,biochemistry,molecular level respectively.The main results were listed as follows:At the individual level,the survival rate and hatching rate of marine medaka performed a good dose-dependent downward trend with the total petroleum hydrocarbons(TPH)concentration of WAFs with varied salinity,and the lowest survival rate and hatching rate were appeared in WAF0.5‰.The obvious developmental malformations of marine medaka induced by WAFs exposure was found following the assessment of blue sac disease(BSD)index,and the order of BSD index was WAF0.5‰ > WAF15‰ > WAF30‰.It indicated that crude oil exposure has stronger teratogenic toxicity under lower salinity.Meanwhile,the incidence of teratogenic endpoints performed a good dose-dependent upward trend with TPH concentration of WAFs,and the teratogenic endpoints related to cardiac were more sensitive to crude oil exposure.At the physiological level,the heart rate,stroke volume,cardiac output of marine medaka performed a good dose-dependent downward trend with TPH concentration of WAFs under varied salinity,the heart rate and cardiac output of marine medaka were lower in WAF0.5‰.This showed that more serve heart dysfunction of marine medaka could be caused by crude oil exposure under lower salinity.Besides,at the biochemistry level,the activity of glutathione Stransferase(GST)and peroxidase(POD)of marine medaka was increased after crude oil exposure,and the activity of GST and POD increased more significantly in WAF0.5‰.At the molecular level,cardiomyocytes excitation-contraction coupling ion channel(atp2a2a)and detoxification genes(ahr1b,cyp1a1)expression were up-regulated significantly.Moreover,in this study,the concentration of TPH and the composition of polycyclic aromatic hydrocarbons(PAHs)in crude oil WAFs were analyzed,the results showed that the TPH concentration of exposed solution were increased with decreased salinity.And the proportion of 2-3 ring PAHs in WAF30‰ was about 5.7% lower than that at WAF0.5‰.This indicated that more TPH and PAHs components could enter into water following the decreased salinity under the same oil loading rate.The marine medaka with high osmatic pressure in lower salinity environment could absorb more TPH and PAHs components either.This may also be the main inducement for the developmental toxicity difference of marine medaka induced by oil spill pollution due to salinity change.The results of this thesis also provided basic data and scientific basis for the subsequent evaluation of the impact and damage of offshore oil spill accidents on the marine environment.