Effects of Copper Nanoparticle Exposure on Physiological Status and Histological Structure of Yellowtail Kingfish (Seriola aureovittata)

Copper nanoparticles (Cu-NPs) are widely used in aquaculture for their growth-promoting and immunoenhancing properties. However, excessive or over-accumulated Cu-NPs in aquaculture water cause toxicity through waterborne immersion. To explore the toxicity effects of waterborne Cu-NPs on yellowtail kingfish (Seriola aureovittata), a 7-day exposure experiment comprising a control group (no Cu-NPs), a low-concentration group (0.120 mg/L), and a high-concentration group (0.384 mg/L) was conducted, followed by a 7-day recovery period without Cu-NP stress. Exposure to Cu-NPs significantly elevated antioxidant enzyme activities (GSH-Px, Cu/Zn-SOD) and thiobarbituric acid reactive substances (TBARS) level in liver and posterior kidney, indicating significant oxidative stress. In the liver, levels of epinephrine and diacylglycerol were significantly upregulated, the cAMP signaling pathway was disrupted, and the NF-κB signaling pathway was activated, along with the downregulation of ap-1 and erk1-2 and upregulation of gadd45β, reducing cell proliferation and viability. These alterations resulted in hepatocellular vacuolation and blurred outlines of hepatic lobules. In the gill, high-concentration Cu-NPs activated oxidative phosphorylation, phagosome, and cell-adhesion molecules pathways and downregulated genes related to cell proliferation, adhesion, and tight junctions (i.e., l1cam, camd1, cntn1, cdh2, and nectin1), leading to cellular vacuolization and epithelial separation in histology. These changes disrupted osmotic balance and significantly upregulated Na+/K+-ATPase activity. All histological damages were not fully recovered within the tested recovery period. Therefore, under conditions of continuous exposure, the concentration of Cu-NPs used for juvenile yellowtail kingfish in aquaculture should be kept below 0.120 mg/L, with a recovery period exceeding 7 days. These results reveal the toxicity mechanisms of Cu-NPs and provide a scientific basis for establishing safe application guidelines in yellowtail kingfish aquaculture.