Toxicological responses of Litopenaeus vannamei to short-term ferric chloride exposure: implications for histopathology, oxidative stress, and intestinal microbiota.

Iron (Fe) contamination in aquaculture environments threatens marine species, particularly Litopenaeus vannamei, with ferric chloride (FeCl3) from industrial uses being a major potential source. This study examines the acute toxicity of FeCl3 in juvenile shrimp through bioaccumulation, histopathology, oxidative stress biomarkers, immune gene expression, and microbiome alterations. Following the determination of the 96-h median-lethal concentration (LC50) of FeCl3 for L. vannamei as 1.194 mg/L, two exposure groups were established; FeC1 (1%) and FeC2 (10%) 96-h LC50 to model low and high sublethal toxicity levels. Bioaccumulation analysis revealed that Fe primarily concentrated in the hepatopancreas, with significantly higher concentrations in Fe-exposed groups compared to controls. Histological analysis showed dose-dependent hepatopancreatic damage, including cell degeneration, lumen collapse, and epithelial necrosis, especially in the FeC2 group. Oxidative stress biomarkers (ROS and MDA) were significantly elevated in Fe-treated groups, with a notable reduction in antioxidant enzyme activities (T-SOD, CAT), and immune parameters (PO, LZM) showed initial activation followed by significant decline. Gene expression analysis indicated transient upregulation of immune (Relish, Toll-2) and antioxidant (Nrf2, GPx, MnSOD) genes, but expression levels of ferritin and lysozyme were suppressed in Fe-exposed shrimp. Microbiome analysis revealed a significant shift towards opportunistic genera such as Enterococcus and Ruegeria in high-dose groups. Functional prediction based on KEGG-pathways indicated enrichment of pathways related to xenobiotic degradation and immune dysfunction, while energy metabolism and immune-related pathways were suppressed. These findings emphasize the significant impact of FeCl3 pollution on shrimp health, indicating the need for strict regulation of iron levels in aquaculture systems.