article · Aquatic Toxicology
Zinc oxide nanoparticles, which are increasingly utilised across industrial, biomedical, and agricultural sectors, accumulate in aquatic ecosystems where they cause deleterious effects on fish. Nile tilapia were exposed to zinc oxide nanoparticles for 28 days to assess whether dietary thymol, administered at one or two grams per kilogram of feed, could alleviate toxicity. Nanoparticle exposure led to leukopenia, lymphopenia, elevated stress markers, reduced serum proteins, diminished immune enzyme activities, and reduced resistance to Aeromonas hydrophila infection. It also downregulated antioxidant gene expression while overexpressing inflammatory genes. Co-supplementation with dietary thymol protected against these immunotoxic effects in a dose-dependent manner. The treatment restored immune indices and enhanced antibacterial resistance, demonstrating that thymol acts as an effective dietary immunostimulant against nanoparticle-induced harm.
Nanoparticle runoff represents an emerging environmental threat that undermines aquatic ecosystem health and commercial aquaculture. Identifying natural feed additives like thymol provides fish farmers and aquaculture managers with a viable dietary approach to shield stock from chemical pollution, bolstering fish immunity and curbing disease outbreaks without relying heavily on synthetic antibiotics.
The findings suggest potential applications in developing thymol-supplemented functional aquafeeds for commercial tilapia farming. Target users include aquafeed manufacturers and aquaculture producers seeking feed-based disease management solutions. Because the research represents applied laboratory testing in aquaria, field validation in commercial farming conditions and safety evaluations will be necessary before feed formulations can be brought to market.
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Zinc oxide nanoparticles (ZnO-NPs) have many exciting properties that make their use in a continuous increase in various biomedical, industrial, and agricultural applications. This is associated with accumulation in the aquatic ecosystems and fish exposure with consequent deleterious effects. To determine the potential of thymol to counteract the immunotoxic effects of ZnO-NPs, Oreochromis niloticus was exposed to ZnO-NPs (⅕ LC50 =1.14 mg/L, for 28 days) with or without feeding a thymol-incorporated diet (1 or 2 g/kg diet). Our data demonstrated a reduction of aquaria water quality, leukopenia, and lymphopenia with a decrease in serum total protein, albumin, and globulin levels in exposed fish. At the same time, the stress indices (cortisol and glucose) were elevated in response to ZnO-NPs exposure. The exposed fish also revealed a decline in serum immunoglobulins, nitric oxide, and the activities of lysozyme and myeloperoxidase, in addition to reduced resistance to the Aeromonas hydrophila challenge. The RT-PCR analysis showed downregulation of antioxidant (SOD) superoxide dismutase and (CAT) catalase gene expression in the liver tissue with overexpression of the immune-related genes (TNF-α and IL-1β). Importantly, we found that thymol markedly protected against ZnO-NPs-induced immunotoxicity in fish co-supplemented with thymol (1 or 2 g/kg diet) in a dose-dependent manner. Our data confirm the immunoprotective and antibacterial effects of thymol in ZnO-NPs exposed fish, supporting the potential utility of thymol as a possible immunostimulant agent.
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DOI: 10.1016/j.aquatox.2023.106523
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