Combined Toxicity of Polyamide Microplastics and Fenitrothion Impairs Growth, Intestinal Integrity, and <scp>GH</scp> – <scp>IGF</scp> Axis in Nile Tilapia

The pervasive contamination of aquatic ecosystems by microplastics (MPs) and organophosphate pesticides raises concerns about their combined impacts on fish physiology, yet empirical evidence remains limited. This study investigated the coexposure effects of polyamide microplastics (PA-MPs, 10 mg/L) and the insecticide fenitrothion (0.3 mg/L) on growth performance, intestinal integrity, and GH-IGF axis regulation in juvenile Nile tilapia (Oreochromis niloticus) over 42 days. Coexposure markedly suppressed somatic growth (weight gain and specific growth rate) and feed efficiency (feed conversion ratio; FCR), exceeding the adverse effects observed under single exposures. Histopathological evaluation revealed significant depletion of goblet cells and enterocytes per villus, indicating pronounced disruption of intestinal epithelium. At the molecular level, gh, igf-1, and igf-2 transcripts were substantially downregulated in the coexposed group, reflecting coordinated impairment of the somatotropic axis. Principal component analysis demonstrated a strong interrelationship among growth, intestinal cellular integrity, and gene expression, collectively delineating the severity of chemical stress. These results suggest potential combined toxicity of co-occurring MPs and organophosphate pesticides, emphasizing their capacity to compromise aquaculture productivity and ecosystem health.