2.3. Microplastic analysis

To determine microplastic ingestion, each fish was killed and dissected, and its digestive tract was transferred to a 100-mL glass beaker covered with aluminum foil. The digestive tracts were digested with 30 % hydrogen peroxide for 72 h at 60 °C。After digestion, the residue in each beaker was filtered onto a Whatman GF/C filter.

To determine microplastic egestion, the residues on the filter collected at each sampling time were rinsed with 30% hydrogen peroxide into a 100-mL glass beaker to digest the faeces and food. After 72 h of digestion, the residues in each beaker were filtered onto a new Whatman GF/C filter. The filters were transferred to glass petri dishes and air-dried. Microplastics on the filters were examined and counted using a Nikon stereomicroscope (Tokyo, Japan) under 20–40 × magnification.