Sub-chronic exposure to copper nanoparticles and copper sulfate dysregulated the microbiota-gut-liver axis in large...

Copper nanoparticles (CuNPs) and copper salts possess promising applications in aquacultural feed additives and medications, but their toxic effects and mechanisms on fish are still not fully understood. This study evaluated the toxic effects of CuNPs and Cu²⁺ (prepared as CuSO₄·5H₂O) on large yellow croaker (Larimichthys crocea) from the microbiota-gut-liver axis. The juvenile L. crocea were exposed to 25 and 75 μg/L CuNPs and 75 μg/L Cu²⁺ for 28 days. The results revealed that 75 μg/L CuNPs inhibited the growth and survival of L. crocea, with gut and liver being the main target organs for Cu accumulation. CuNPs disrupted the homeostasis of gut microbiota, leading to an increase in the levels of harmful bacteria (e.g., Cutibacterium, Staphylococcus, and Pseudomonas) and endotoxin (lipopolysaccharide, LPS), as well as a severe impairment of the intestinal barrier function (e.g., intestinal structure, mucous cells, and biochemical indicators), and inducing oxidative stress, apoptosis, inflammation, and lipid deposition in the liver. This process also caused LPS produced by gut microbiota to translocate to the liver, thereby potentially influencing hepatic physiology and metabolism. Moreover, although Cu²⁺ also induced changes in the intestine and liver, its toxic effects were different from CuNPs (e.g., in gut microbiota composition, apoptotic pathways, and lipid content), with CuNPs exhibiting higher toxicity to L. crocea. Overall, the microbiota-gut-liver axis is an important pathway for the toxicity of CuNPs and Cu²⁺. Our study provides a theoretical reference for the safe application of CuNPs and copper salts in aquaculture of marine fish such as L. crocea.