The present study aimed at assessing the singular and combined effects of water copper and polyvinyl chloride microplastic (MPVC) on intestinal copper accumulation, histopathological damage, and stress‐/immune‐related genes' expression in common carp, Cyprinus carpio. Four groups of fish were maintained in triplicate: control (kept in clean water), Cu (exposed to 0.25 mg/L of copper), MPVC (exposed to 0.5 mg/L of MPVC), and Cu‐MPVC (exposed to 0.25 mg/L of copper + 0.5 mg/L of MPVC). After 14‐day exposure, the fish of Cu and Cu‐MPVC treatments exhibited significantly higher intestinal copper contents, compared to the fish of control and MPVC treatments. In this regard, the Cu‐MPVC fish had significantly higher copper content than the Cu fish. Exposure to copper and/or MPVC significantly upregulated the intestinal heat shock protein 70 (hsp70), cytochrome P450 family 1 subfamily A member 1 (cyp1a1), lysozyme (lys), defensin (def), mucin 2 (muc2), and mucin 5 (muc5) expression. The highest expression of hsp70, cyp1a1, lys, and def was related to Cu‐MPVC treatment; whereas, the highest expression of muc2 and muc5 was observed in Cu and MPVC treatments. Exposure to copper and/or MPVC induced intestinal damage, which Cu‐MPVC fish exhibited the highest severity. The present study revealed that exposure to copper and/or MPVC causes intestinal histopathological damage and upregulation in stress‐ and immune‐related genes' expression. The most serious effects were observed in Cu‐MPVC treatment that might be due to additive effects of copper and MPVC and/or higher copper accumulation in this treatment.

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Silver nanoparticles are the most important nanomaterials for antibacterial uses and are famous for their strong inhibitory and antibacterial effects. In recent years, extensive studies have been undertaken on the use of antimicrobial properties of silver, incorporated within aquaculture industry. To evaluate the scientific basis for the use of the nano silver in shrimp aquaculture, in this study the antimicrobial activities of colloidal nano silver with two different sizes (16.62 and 22.22 nm) was evaluated against gram negative bacteria, V. harveyi. Before the experiments, cAgNPs were characterized using several analytical techniques. Well diffusion method, micro-dilution tests (MIC and MBC) and kinetic of death were used to evaluate the bactericidal activity of the nanoparticles. Results showed that MIC and MBC values of cAgNPs in both studied sizes are equal (MIC = MBC). Best bactericidal kinetics in the presence of 16.62 and 22.22 nm nanoparticles obtained at 4 and 6 h, respectively. The obtained results suggested that smaller silver nanoparticles had a faster antibacterial activity than the larger particles. According to the obtained results, the activity of cAgNPs against V. harveyi is fast and has potential for the treatment of bacterial infection in aquaculture.

Common carp, Cyprinus carpio, is one of the most important aquaculture species in the world. About 4.6 million tones common carp are annually produced, accounting for 8% of the world's total finfish production (FAO, 2020). Increased global demand for edible fish has led to progressive increase in fish rearing density to increase yield and land-use efficiency; however, such a rearing intensification has

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