Protective effects of Astragalus membranaceus polysaccharide against aluminum oxide nanoparticle-induced growth retardation and oxidative-immunological disruption in Oreochromis niloticus.

Although the toxicity of aluminum-based nanoparticles (Al2O3-NPs) in fish has been widely studied, strategies to mitigate their harmful effects remain limited. Moreover, the modulatory role of Astragalus membranaceus polysaccharides (APS) under this toxic stress is still poorly understood, despite the widespread presence of Al2O3-NPs in aquatic ecosystems and the need for effective mitigation strategies for sustainable aquaculture. In this study, Oreochromis niloticus was exposed to Al2O3-NPs (10 mg/L) with or without dietary APS (1.5 or 3 mg/kg) for four weeks. A total of 270 fish (initial weight = 25.28 ± 0.086 g) were randomly distributed into six triplicate groups (n = 15 per group) as control, APS (1.5 mg/kg–3 mg/kg), Al2O3-NPs, and two co-treated groups (Al2O3-NPs + APS). Al2O3-NPs exposure showed significant effects on growth performance compared to the control group (P < 0.05), as shown by the decrease in final weight (FW: -9.4%), weight gain (WG: − 21.4%), specific growth rate (SGR: -17.1%), along with an increase in feed conversion ratio (FCR: + 16.9%). Liver function was severely affected, as evidenced by an increase in ALT levels (+ 39%) and decrease in total protein (− 26.5%) and IgM levels (− 19.3%) (P < 0.05). In addition, the expression of antioxidant-related genes, such as CAT and SOD, was downregulated, while the expression of pro-inflammatory cytokines, such as TNF-β and IL-1β, as well as stress-related gene, such as MT, was upregulated in the liver and gills (P < 0.05). Histopathological examination showed noticeable degenerative and necrotic changes in the liver, kidney, muscle, gill, and spleen tissues. Co-treatment with APS, particularly at 3 mg/kg, significantly improved growth parameters (FW, 20.3% increase; WG, 53.1% increase; and SGR, 38.8% increase) (P < 0.05), ameliorated hepatic and renal histopathological changes, restored antioxidant gene expression and normalized inflammatory mediators compared with the Al2O3-NPs-exposed group. Compared with the Al2O3-NPs–exposed group, the survival rate increased by 5.3%, ALT levels decreased by 60.1%, while total protein and IgM levels increased by 29.6% and 8.9%, respectively. Overall, APS supplementation effectively mitigated Al2O3-NPs-induced toxicity in O. niloticus by regulating antioxidant capacity, suppressing inflammatory responses, and improving tissue structure, highlighting its potential as an eco-friendly functional food additive to protect fish health under nano-toxic stress.