Transcriptome and Gene Family Analyses Reveal the Physiological and Immune Regulatory Mechanisms of Channa maculata Larvae in Response to Nanoplastic-Induced Oxidative Stress

The increasing accumulation of plastic debris in aquatic environments has raised concerns about the ecotoxicological effects of polystyrene nanoplastics (PSNPs). This study examined PSNPs toxicity during a critical developmental stage by exposing 15 days post-fertilization (dpf) larvae of blotched snakehead (Channa maculata), an economically important freshwater fish, to PSNPs concentrations of 0.05–20 mg/L for 15 days. Histopathological analysis showed concentration-dependent damage, including hepatocellular vacuolization (5–10 mg/L) and hepatic sinusoidal dilation (20 mg/L) in the liver, alongside intestinal injuries ranging from villus erosion to rupture (5–20 mg/L). Biochemically, PSNPs triggered a biphasic oxidative response, where superoxide dismutase (SOD) and catalase (CAT) activities peaked at 5 mg/L before declining, while malondialdehyde (MDA) levels exhibited an opposite trend. Transcriptomic analysis and Quantitative real-time PCR (qRT-PCR) indicated that PSNPs disrupted growth, energy metabolism, and immune regulation in C. maculata larvae, evidenced by the dysregulation of growth hormone/insulin-like growth factor (GH/IGF) axis genes and up-regulation of immune-related genes. Furthermore, Weighted Gene Co-expression Network Analysis (WGCNA) identified the heterogeneous nuclear ribonucleoproteins (HNRNP) gene family as hub genes from the key turquoise module, suggesting that PSNPs interfere with RNA processing and post-transcriptional control. In summary, PSNPs caused multi-level toxicity in C. maculata larvae, providing new insights into their ecotoxicological hazards in freshwater ecosystems.