Combined polyvinyl chloride microplastic exposure and Vibrio parahaemolyticus challenge are associated with hepatopancreatic injury and production losses in Pacific white shrimp.

Microplastic particles and bacterial pathogens can co-occur in shrimp-production systems, but experimental designs without particle-only treatments cannot establish a statistical interaction between these stressors. This study therefore evaluated biological outcomes during combined polyvinyl chloride microplastic (PVC-MP) exposure and Vibrio parahaemolyticus challenge in Pacific white shrimp (Litopenaeus vannamei). Five treatments, each with three replicate containers, comprised an unexposed negative control (KN), a bacterial-challenge control (KP), and combined treatments containing nominal PVC-MP concentrations of 3, 30, or 300 mg L-1 (P1-P3) followed by a 104 CFU mL-1 immersion challenge. PVC-MP pre-exposure lasted 15 days and survival was recorded for 7 days after challenge. Light-microscopy counts after hydrogen-peroxide digestion increased from 17.66 to 18.14 particles g-1 in the controls to 74.28, 171.28, and 217.44 particles g-1 in P1-P3. These values are reported as putative digestive particle counts because recovered-particle identity was not confirmed by FTIR or Raman spectroscopy and analytical recovery was not validated. Survival declined from 83.33% in KN and 66.67% in KP to 48.33%, 26.67%, and 21.67% in P1-P3. Representative histology showed increasingly severe tubule dilation, degeneration, epithelial cytolysis, abnormal lumina, B-cell enlargement, and hemocytic infiltration in the combined-exposure groups. FCR, not corrected for mortality, increased, while SGR, container-level net biomass gain, and length gain declined. These findings support a dose-linked, treatment-associated pattern of putative digestive particle counts, hepatopancreatic injury, and production loss under bacterial challenge. Interpretation is limited by the absence of PVC-only treatments, FTIR/Raman confirmation, particle-recovery controls, mortality-corrected FCR, and direct quantification of V. parahaemolyticus on PVC surfaces.