Larvae from the marine medaka fish Oryzias javanicus were exposed with polystyrene microplastics (MPs) for 24 h. Exposure to waterborne fluorescent MPs showed clear ingestion and egestion in feces. Under constant MPs, the concentration of dissolved oxygen significantly decreased in 24 h compared to the control. Significant intracellular reactive oxygen species and malondialdehyde contents were detected in larvae, indicating oxidative stress and lipid peroxidation. Significant elevations in mRNA expressions of heat shock protein 70 and antioxidant defense system genes (glutathione reductase, glutathione peroxidase, catalase, and superoxide dismutase) were measured with increases in enzymatic activity of oxidative stress-related proteins. Taken together, the alterations to the molecular and biochemical components suggested that waterborne MPs had an oxidative stress effect on marine medaka larvae.

Introduction
Materials and Methods
    1. Marine medaka
    2. Microplastics exposure
    3. Measurement of intracellular reactive oxygenspecies and lipid peroxidation
    4. Total RNA extraction
    5. Real-time polymerase chain reaction
    6. Measurement of antioxidant defense systemenzyme activities
    7. Statistical analysis
Results and Discussion

• Jae-Sung Rhee(Department of Marine Science, College of Natural Sciences, Incheon National University, Incheon 22012, Korea, Research Institute of Basic Sciences, Incheon National University, Incheon 22012, Korea, Institute of Green Environmental Research Center, Incheon 21999, Korea ) Corresponding author
• Jee-Hyun Jung(Risk Assessment Research Center, Korea Institute of Ocean Science and Technology, Geoje 53201, Korea)
• Sang-Eun Nam(Department of Marine Science, College of Natural Sciences, Incheon National University, Incheon 22012, Korea)